National Calculation Methodology (NCM) - Scottish Government

Directorate for the Built Environment 

Building Standards Division 

National Calculation 

Methodology (NCM) 

Modelling Guide for Non- 

Domestic Buildings in 

Scotland

Report Prepared by: 

Building Research Establishment (BRE) 

Bucknalls Lane 

Watford 

WD25 9XX 

01923 664000 

enquiries @bre.co.uk 

The opinions expressed in this report are those of the author. 

Report commissioned by: 

Directorate for the Built Environment 

Building Standards Division 

Denholm House 

Almondvale Business Park 

Livingston 

EH54 6GA 

Tel: 01506 600 400 

Fax: 01506 600 401 

e-mail: buildingstandards@scotland.gsi.gov.uk 

web: http://www.scotland.gov.uk/bsd 

© Crown Copyright 2010 

Applications for reproduction of any part of this publication should be addressed to: 

BSD, Directorate for the Built Environment, Denholm House, Almondvale Business 

Park, Livingston, EH54 6GA 

This report is published electronically to limit the use of paper, but photocopies will be 

provided on request to Building Standards Division. 

2

Contents. 

Contents 3 

List of Tables 4 

Acronyms Used in this Guide 5 

1 Introduction 6 

2 Approved Software Tools 7 

Versions Policy 8 

Choosing a Software Tool 8 

SBEM Constraints 9 

3 Compliance with Building Regulations 10 

Definition of the Notional Building 10 

Building Fabric 11 

Solar and Daylight Transmittance 13 

Areas of Windows, Doors and Rooflights 13 

HVAC System Definition 14 

Installed Lighting Power Density 18 

The Target Emission Rate (TER) 19 

Modular and Portable Buildings 21 

Shell Buildings 21 

Extensions to the Insulation Envelope 22 

4 Energy Performance Certificates (EPCs) 23 

Other reference values 24 

5 Input Data to Approved Tools 25 

Defining internal gains and environmental conditions 25 

Constructions 26 

Low and zero carbon systems 26 

Weather Location 27 

Zoning Rules 27 

Measurement and Other Conventions 28 

6 NCM Databases 30 

Activity Database 30 

Construction and Glazing Databases 37 

7 Suitability of Calculation Method 42 

Availability of Tools and Competence of Users 42 

The Complexity of the Building and its Services 42 

Whether Workarounds are Available 43 

Limitations of all Software Tools 43 

Users of the Software 44 

3

List of Tables. 

Table 1: U-values of construction elements in the notional building 11 

Table 2: Thermal capacity of construction elements in the notional building 12 

Table 3: Solar and daylight transmittances in the notional building 13 

Table 4: HVAC Seasonal system efficiencies in the notional building 17 

Table 5: Specific fan power for different ventilation systems in the notional building 18 

Table 6: Carbon dioxide emission factors 21 

Table 7: EPC scale and energy labels 24 

Table 8: Measurement and other conventions 28 

Table 9: List of building types in the Activity Database with definitions 32 

Table 10: List of activity types in the Activity Database with definitions 33 

Table 11: Scottish opaque constructions in the NCM Construction Database 37 

Table 12: Scottish transparent constructions in the NCM Glazing Database 41 

4

BER Building Emission Rate 

BSD Building Standards Division 

Acronyms Used in this Guide. 

CAD Computer-Aided Design 

CEN Comité Européen de Normalisation (The European Committee for 

Standardisation) 

CHP Combined Heat and Power 

CIBSE The Chartered Institution of Building Services Engineers 

CO2 Carbon dioxide 

DSM Dynamic Simulation Model 

EER Energy Efficiency Ratio 

EPC Energy Performance Certificate 

HEPA High Efficiency Particulate Air 

HVAC Heating Ventilation and Air Conditioning 

IF Improvement Factor 

iSBEM Interface to Simplified Building Energy Model 

NCM National Calculation Methodology 

SBEM Simplified Building Energy Model 

SCoP Seasonal Coefficient of Performance 

SFP Specific Fan Power 

SSEER Seasonal System Energy Efficiency Ratio 

TER Target Emission Rate

1 Introduction. 

1. This document gives guidance on the use of SBEM and other approved software 

tools comprising the National Calculation Methodology (NCM) when: 

a. Demonstrating compliance with the carbon emission requirements of Section 6 

in respect of non domestic buildings. 

b. Calculating asset ratings as part of preparing Energy Performance Certificates 

(EPCs) for non domestic buildings, as required by the Energy Performance of 

Buildings (Scotland) Regulations 2008. 

2. With regards to paragraph 1.b above, it is expected that Approved Organisations 1 

have produced separate guidance regarding the forward transmission of the 

results of these calculations for the purposes of the formal issue of the EPC and 

the Recommendation Report for the building to the building owners. 

3. Separate guidance has been published for the application of the methodology 

when using approved tools to demonstrate compliance with the applicable 

regulations in England and Wales or Northern Ireland. 

4. This document is subject to regular review and it will be updated as and when the 

need for additional clarification is identified. This routine updating will help improve 

the consistency of application of the various tools to the building regulations 

compliance and energy certification processes. The latest version of the NCM 

Modelling Guide for Scotland will be available on the website of the Scottish 

Government Building Standards Division 2 (BSD) when published and each new 

version supersedes the previous ones. 

1 

‘ Approved Organisations’ are referred to as ‘Protocol Organisations’ in iSBEM and the iSBEM User 

Guide. 

2 

The Directorate for the Built Environment, Building Standards Division, www.scotland.gov.uk/bsd.

2 Approved Software Tools. 

5. Non-domestic building energy calculation software packages for compliance and 

certification of energy performance of buildings must be approved by the Scottish 

Government Building Standards Division 3 (BSD) before they can be available for 

commercial use in Scotland. Information on the validation procedure and the 

approval scheme is available from the BSD. 

6. The BSD website lists software approved for demonstrating compliance with 

Section 6 and for calculating ratings as part of the production of an Energy 

Performance Certificate (EPC) in Scotland. The website also provides a list of 

Approved Organisations who can accredit persons wishing to engage in the 

production of EPCs for existing non-domestic buildings in Scotland 4 and 

information on the use of Approved Certifiers of Design for Section 6 (Energy) 5 in 

support of a building warrant application. 

7. To be approved, the software tool must satisfy the criteria as published 6 by the 

BSD. These requirements are updated from time to time and cover a number of 

generic issues. The software tool has to demonstrate that: 

a. The calculations are technically robust and that they cover a necessary 

minimum set of energy flows. 

b. It follows the procedures for demonstrating compliance and issue of Energy 

Performance Certificates as defined in this document, including the use of the 

National Calculation Methodology (NCM) databases, the definition of notional 

building, and other issues as defined from time to time. 

c. It reports a minimum set of output parameters and that these parameters can 

be passed appropriately to standard modules for: 

i. Checking compliance with Section 6 

ii. Producing an Energy Performance Certificate (EPC) 

iii. Deriving a set of recommendations for energy efficiency improvements. 

8. In addition to ensuring that the software tools are compatible in terms of technical 

scope, the approval process also requires software providers to check that the 

procedural guidance is being followed in terms of the calculation and reporting 

processes. 

3 The Directorate for the Built Environment, Building Standards Division, www.scotland.gov.uk/bsd. 

4 http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building- 

standards/profinfo/epcintro/epcguidadvice. 

5 http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building-standards/profinfo/cert 

6 http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building- 

standards/profinfo/techguide/proftechS6software.

Versions Policy 

9. All software tools, both the government’s Simplified Building Energy Model 

(SBEM) and commercial Dynamic Simulation Models (DSMs), evolve with time as 

improvements are made to the functionality and the quality of the underlying 

algorithms. This means that it is necessary to have a procedure whereby new 

versions can be accepted as appropriate for use within the compliance/certification 

process. The rules in the following paragraphs define the approved procedures. 

10. For certifying compliance with Section 6, when submitting a building warrant: 

a. The latest version of a software tool should generally be used. 

b. The previous version of a software tool (i.e. software and NCM databases) may 

be used for a period not exceeding six months following introduction of a new 

version, provided a change in regulations does not require use of the current 

version (as would be the case, for example, from 1 October 2010). 

c. Whilst the same version of a software tool may be used for any amendment to 

warrant as for the original warrant, at any stage, applicants can elect to adopt a 

more recently approved version of the tool, but having elected to use a later 

version, building developers cannot subsequently revert to using a previous 

one. 

11. For the production of Energy Performance Certificates, the most recently approved 

version of the adopted software tool must be used, unless the latest version has 

been released less than one calendar month prior to the assessment date. In such 

cases, the previous version of the tool may be used, provided a change in 

regulations does not require use of the current version. 

12. To allow the transfer and reuse of project data from an older to a newer version of 

the tool, part of the procedure for approving a software tool is that a new version 

must be backwardly compatible with all previous versions of the tool, i.e. it can 

either read the data files of previous versions directly, or a file conversion utility 

must be provided. 

Choosing a Software Tool 

13. While all calculation methods involve a degree of simplification, two classes of 

software tools are available for use for Section 6 compliance checking and EPC 

generation: 

a. SBEM, which is the Simplified Building Energy Model developed for the BSD. 

This can be applied to any building (irrespective of size) although there are 

some constraints, as discussed in Chapter 7 of this guide. Such constraints are 

for example, where representation of certain building features require some 

approximation, entailing additional demands of the assessor’s input time and 

effort; and 

b. Approved Dynamic Simulation Models (DSMs). These are applicable for any 

building unless an individual DSM’s approval specifically excludes certain types 

8

of building or building features. They may prove more flexible than SBEM in 

handling certain building features and are also more suited as design support 

tools (SBEM is not a design tool, carrying out compliance and certification 

calculations only). 

14. There are a number of approved software interfaces to SBEM. These interfaces 

must also be approved before the overall software tool can be used. Interface 

approval as well as software approval is necessary to ensure that procedures are 

followed appropriately as well as the calculations being carried out correctly. 

SBEM Constraints 

15. All calculation processes involve some approximations and compromises, and 

SBEM is no exception. The most obvious limitations relate to the use of the CEN 

monthly heat balance method. This means that processes which vary non-linearly 

at shorter time-steps have to be approximated or represented by monthly 

parameters. The HVAC system efficiencies are an example of this. 

16. It is, therefore, difficult to give absolute rules about when SBEM can and cannot be 

used. As broad guidance, it is more likely to be difficult to use SBEM satisfactorily 

if the building and its systems have features that: 

a. Are not already included in SBEM; or 

b. Have properties that vary non-linearly over periods of the order of an hour. 

17. It should be noted that there are also constraints to the use of other software. Any 

software tool has limits to the building and system options that it can model. 

18. Guidance on the suitability of the calculation method is provided in Chapter 7 of 

this guide. 

9

3 Compliance with Building Regulations. 

19. Compliance with Standard 6.1 of Section 6 requires that a new non domestic 

building must show, by calculation, that it is designed to limit carbon dioxide 

emissions. This is achieved by demonstrating that the building as designed will 

have emissions no greater than a Target Emission Rate (TER), i.e. the Building 

Emission Rate (BER) is less than or equal to the TER. 

20. The TER is based on the performance of a “notional building” and the following 

procedure must be followed in order to establish the TER. This approach is 

adopted to avoid the need to define system models appropriate to different types 

of building. It also ensures a consistent approach to the target setting process. 

Definition of the Notional Building 

21. As specified in the guidance under Standard 6.1 of Section 6, the notional building 

must have the same size, shape, and zoning arrangements as the actual building, 

with the same conventions relating to the measurement of dimensions (see table 8 

below). 

22. Each space must contain the same activity (and therefore the same activity 

parameter values) as proposed for the equivalent space in the actual building. The 

activity in each space must be selected from the list of activities as defined in the 

NCM Activity Database (see paragraph 75 and Chapter 6 of this guide). 

23. The notional and actual buildings must be given the same orientation and be 

exposed to the same weather. For DSM software 7 , the notional building must be 

subject to the same site shading from adjacent buildings and other topographical 

features as are applied to the model of the actual building. 

24. Whatever servicing strategy (heating, ventilation, cooling) is specified in a zone in 

the actual building must also be provided in the corresponding zone in the notional 

building. Note that in some zones, heating need not be provided, even though the 

NCM Activity Database specifies a heating set-point. For example, the actual 

building may contain an unheated stairwell or atrium space. The corresponding 

zones in the notional building must also be unheated. However, if heating were 

provided to either of these spaces in the actual building, then heating must 

correspondingly be specified in the notional building, and then both buildings must 

heat those spaces to the heating set-point specified for the zone type in the NCM 

Activity Database. 

25. Any building services system not covered by Section 6 must be ignored in both the 

actual and notional buildings. 

7 This does not apply to SBEM where external shading is not modelled.

Building Fabric 

26. The U-values in the notional building must be as specified in Table 1. Taking into 

account guidance in BR 443 8 , all U-values should be calculated in accordance 

with BS EN ISO 6946: 2007, where the U-values calculation methods are inclusive 

of repeating thermal bridges. The reference constructions conforming to these Uvalues 

are identified in Table 1 by their reference identities. In addition, the general 

guidance beginning at paragraph 78 must be followed. 

Table 1: U-values of construction elements in the notional building 

Exposed element U-value (W/m 2 K) Database 

reference IDs 

Pitched † roofs 0.16 236 

Flat roofs 0.25 291 

Walls 0.30 295 

Ground and other exposed floors (see 

paragraph 30) 

0.25 248 

Windows * and rooflights 2.2 ‡ See Table 3 

External personnel doors 2.2 480 

Vehicle access and similar large doors 1.5 261 

Internal walls 2.0 307 

Internal windows 3.85 481 

Internal floors viewed from room above 1.25 355 

Internal floors viewed from room below 1.23 315 

† o o 

A pitched roof is one with a pitch greater than 10 and less than or equal to 70 . Any part 

of a roof with a pitch greater than or equal to 70 o is considered a wall. 

‡ 

This U-value relates to the performance of the unit in the vertical plane. The U-value 

must be adjusted for slope as detailed in section 11.1 of BR 443. 

* 

Glazed doors are treated as windows (see Table 8 below). 

27. In addition, the U-values of display windows must be taken as 5.7 W/m 2 K in both 

the notional building and the actual building. 

28. Smoke vents and other ventilation openings such as intake and discharge grilles 

must be disregarded in both the notional and actual buildings, and their area 

substituted by the relevant (i.e. immediately surrounding) opaque fabric (roof or 

wall). 

29. Non-repeating thermal bridge heat losses for each element (including windows, 

etc.) must be accounted for by using the ψ (psi) values specified in clause 6.1.4 of 

Section 6. Note that the U-values as given in Table 1 do not include any allowance 

for heat losses through non-repeating thermal bridges, and so the calculation tool 

must make the adjustment explicitly. 

8 

Conventions for U value calculations, BRE, 2006. 

11

30. Special considerations apply to ground floors in the notional building, where the Uvalue 

is a function of the ‘perimeter/area’ ratio. The following adjustments 9 must 

be made: 

a. If the calculated U-value is greater than 0.25 W/m 2 K, the value of 0.25 W/m 2 K 

must be used in the notional building. 

b. If the calculated U-value is less than 0.25 W/m 2 K with no added insulation, this 

lower value must be used in the notional building. 

31. When modelling an extension, the boundary between the existing building and the 

extension must be disregarded (i.e. assume no heat transfer across it). 

32. The effective thermal capacity of the construction elements, κm (kappa-m) value, in 

the notional building must be as shown in Table 2 (the thermal mass of windows 

should be ignored). DSMs must use the construction elements whose reference 

IDs are given in Table 1. The information in the NCM Construction Database 

includes the necessary technical parameters to evaluate the impact of thermal 

capacity. 

Table 2: Thermal capacity of construction elements in the notional building 

Element κm, Effective thermal capacity* (kJ/m 2 K) 

Roofs 12 

Walls 11.7 

Floors 36 

Internal wall 11.9 

Internal floor (and ceiling) 8.6 

* Effective thermal capacity, κm, is defined in EN ISO 13790 

33. The air permeability of the notional building must be defined as 10m 3 /(h.m 2 

envelope area) at 50 Pa. The calculation method used to predict the infiltration rate 

must use the air permeability as the parameter defining the envelope leakage. For 

compliance and certification purposes, the same method must be used in the 

actual and notional buildings. Acceptable methods include: 

a. The method specified in EN 15242 10 . 

b. Other methods that use a relationship between the infiltration rate and air 

permeability and are set out in national or international standards, or 

recognised in UK professional guidance documents, which relate the average 

infiltration rate to envelope permeability. An example of the latter would be 

tables 4.13 to 4.20 of CIBSE Guide A (2006). 

9 

This follows the guidance given in CIBSE Guide A (2007). 

10 

Ventilation for buildings – Calculation methods for the determination of air flow rates in buildings 

including infiltration, EN 15242, CEN/TC 156, 2006. 

12

Methods that use flow networks are not acceptable for compliance or certification 

of energy performance of buildings purposes as there is no simple way to check 

that the permeability of the notional building delivers the required permeability 

standard. 

Solar and Daylight Transmittance 

34. The total solar energy transmittance (BS EN 410 g-value) and the daylight 

transmittance of glazing in the notional building must be as given in Table 3. These 

data apply to all windows, roof windows, and rooflights (for display windows, solar 

transmittance is 0.72 and daylight transmittance 11 is 0). The data in the tables are 

based on a normal incidence value of 0.72 for solar transmittance and 0.76 for 

daylight transmittance, which are further adjusted for certain orientations in order 

to limit overheating in the notional building. Appropriate values for intermediate 

orientations can be based on linear interpolation. DSMs must use the glazing 

element as identified by the reference IDs in the NCM Glazing Database for 

Scotland. 

Table 3: Solar and daylight transmittances in the notional building 

Orientation of 

glazing 

Solar transmittance 

(BS EN 410 g-value) 

Daylight 

transmittance 

N 0.72 0.76 274 

NE 0.72 0.76 276 

E 0.58 0.61 277 

SE 0.58 0.61 278 

S 0.72 0.76 279 

SW 0.58 0.61 280 

W 0.58 0.61 281 

NW 0.72 0.76 282 

Horizontal 0.43 0.46 275 

Areas of Windows, Doors and Rooflights 

Database 

reference IDs 

35. The areas of windows, doors and rooflights in the notional building must be 

determined as set out in the following sub-paragraphs and must also conform to 

the measurement conventions set out in the guidance beginning at paragraph 87. 

a. Subject to the following criteria, all external walls must have windows and, for 

industrial and storage buildings, roofs must have rooflights. 

b. Copy into the notional building the areas of pedestrian doors (high-usage 

entrance doors in the actual building should be copied as personnel doors in 

the notional building), vehicle access doors and display windows that exist in 

the corresponding element of the actual building. 

11 The daylight transmittance of display windows in the actual building is also set to 0. 

13

c. If the total area of these elements is less than the appropriate allowance from 

clause 6.1.4 of Section 6, the balance must be made up of windows or 

rooflights as appropriate. 

d. If the total area of the copied elements exceeds the allowance from clause 

6.1.4 of Section 6, the copied areas must be retained, but no further area of 

windows or rooflights added. As noted in paragraph 28, smoke vents and other 

ventilation openings must be ignored in both the notional and actual buildings. 

e. The areas shown in clause 6.1.4 of Section 6, represent the areas of openings 

in the wall or roof and comprise the area of the glass plus the frame. The 

windows must have a frame factor of 0.1 (i.e. 90% of the area of the opening is 

glazed) and rooflights a frame factor of 0.3 (display windows have a frame 

factor of 0.1). 

36. In addition, the following rules apply: 

a. In the notional building, pedestrian and vehicle access doors must be taken as 

being opaque, i.e. with no glazing. 

b. No glazed area should be included in basements. In semi-basements, i.e. 

where the wall of the basement space is partly above ground, the percentages 

in clause 6.1.4 of Section 6 must include the above-ground part, with no 

glazing allowance for the below-ground part. 

HVAC 12 System Definition 

37. Each space in the notional building will have the same level of servicing as the 

equivalent space in the actual building. In this context, “level of servicing” means 

the broad category of environmental control, i.e. 

a. Unconditioned (i.e. neither heated nor mechanically cooled) 

b. Heated only with natural ventilation 

c. Heated only with mechanical ventilation 

d. Air-conditioned (i.e. heated and mechanically cooled) 

e. Mixed-mode cooling, where cooling operates only in peak season to prevent 

space temperatures exceeding a threshold temperature higher than that 

normally provided by an air-conditioning system. This can be accompanied by 

either natural or mechanical ventilation. 

38. A space is only considered as having air-conditioning if the system serving that 

space includes refrigeration. Night cooling using mechanical ventilation is not airconditioning. 

If the same mechanical ventilation system that is used for night 

cooling is also used to provide normal ventilation, then the space should be 

12 Heating Ventilation and Air Conditioning. 

14

egarded as being mechanically ventilated. Any boosted supply rate required to 

limit overheating must be ignored in the notional and actual buildings. If the 

mechanical ventilation system only operates in peak summer conditions to control 

overheating, and during normal conditions ventilation is provided naturally, then 

the space must be regarded as naturally ventilated, and the mechanical ventilation 

system can be ignored in both the notional and actual buildings. 

39. If a zone is naturally ventilated, the modelling strategy must provide for enhanced 

natural ventilation in the notional building to prevent overheating. If this is not 

done, heat will build up and artificially depress the demand for heating the next 

day, thereby making the energy target unrealistically harsh. For DSMs 13 , the 

following modelling strategy must be used in the notional building. The strategy 

must increase the natural ventilation rate to 5 ac/h whenever the space 

temperature exceeds the heating set-point 14 by 1 K. This enhanced ventilation 

must cease immediately once the space temperature falls below the heating setpoint. 

By maintaining the increased natural ventilation until internal temperatures fall to 

the (high) heating set-point, the temperatures at start-up next day will be neither 

artificially high nor low. 

40. Humidity control is ignored in both the notional and actual buildings. 

41. The following fuel must be used for space and water heating services in the 

notional building: 

a. Where mains gas is available on site (even if it does not supply any heating 

services in the actual building), mains gas must be used in the notional building 

to supply both space and water heating. 

b. Where mains gas is used for any space or water heating in the actual building, 

mains gas must also be used in the notional one. This means that if mains gas 

is used for heating, but another fuel is used to supply hot water (or vice versa), 

then in the notional building, gas must be used for both services on the basis 

that it is available. 

c. Where neither paragraph 41.a nor paragraph 41.b applies, oil must be used for 

space and water heating services in the notional building. 

d. For the purposes of this guide, the ‘main heating fuel’ should be taken as the 

fuel which delivers the greatest total thermal output (space or water heating) 

over the year. If there are multiple devices served by the same fuel, the 

relevant total thermal output is the sum of all the outputs for the devices served 

by that fuel. 

13 

Such an approach is not needed in SBEM since the form of the model means that there is no 

feedback between overheating on one day and the energy demands on the next. 

14 

This guidance assumes that the zone heat output is zero when the heating set-point is exceeded. If 

models use a proportional band to modulate heating output, the heating set-point in this context 

should be regarded as the temperature at the top of the proportional band, not its mid-point. 

15

42. The cooling and auxiliary energy in the notional building must be taken to be 

powered by grid-supplied electricity. 

43. The efficiency of the HVAC systems in the notional building must be as given in 

Table 4. 

44. The system performance definitions follow the practice set out in EN 15243 15 : 

a. Auxiliary energy is the energy used by controls, pumps and fans associated 

with the HVAC systems. It is the term described as “fans, pumps, controls” in 

Energy Consumption Guides such as ECG019 16 . The auxiliary energy demand 

must be calculated as detailed in paragraph 0 as appropriate. 

b. The Seasonal Coefficient of Performance for heating (SCoP 17 ) is the ratio of 

the sum of the heating demands of all spaces served by a heating system to 

the energy content of the fuels (or electricity) supplied to the boiler or other 

heat generator of the system. The SCoP includes, amongst other things, the 

efficiency of the heat generator, thermal losses from pipework and ductwork, 

and duct leakage. It does not include the energy used by fans and pumps (but 

does include the proportion of that energy that reappears as heat within the 

system). For DSMs, the ventilation air supplied to the zone must be taken as at 

the outdoor air temperature. For SBEM, adjusted monthly average figures 

should be used. Heating energy consumption is, therefore, calculated from the 

following expression: 

HeatingEnergyConsumption = ∑ 

( ZoneHeatingLoad 

) SCoP 

c. The Seasonal System Energy Efficiency Ratio for cooling (SSEER) is the ratio 

of the sum of the sensible cooling demands of all spaces served by a cooling 

system to the energy content of the electricity (or fuel) supplied to the chiller or 

other cold generator of the system. The SSEER includes, amongst other 

things, the efficiency of the cold generator, heat gains to pipework and 

ductwork, duct leakage, and removal of latent energy (whether intentional or 

not). It does not include energy used by fans and pumps (but does include the 

proportion of that energy that reappears as heat within the system). The 

electricity used by heat rejection equipment associated with chillers is 

accounted for in the SSEER (not as auxiliary energy). The electricity used 

within room air-conditioners for fan operation is also included in the SSEER 

value since it is included in the standard measurement procedure for their 

Energy Efficiency Ratio (EER). For DSMs, the temperature of the ventilation air 

supplied to the zone must be taken as that of the outdoor air temperature. For 

SBEM, adjusted monthly average figures should be used. Cooling energy 

consumption is, therefore, calculated from the following expression: 

CoolingEnergyConsumption = ∑ 

( ZoneCoolingLoad 

) SSEER 

15 

EN 15243, Ventilation for Buildings – Calculation of room temperatures and of load and energy for 

buildings with room conditioning systems, CEN, 2007. 

16 

Energy use in offices, Energy Consumption Guide 19, Action Energy, 2003. 

17 

This is referred to as Seasonal System Efficiency (SSEff) in the iSBEM User guide. 

16

d. The electricity used by fossil-fuelled equipment and its ancillaries, including 

fans in unit heaters and gas boosters, is included in the auxiliary energy. 

e. For the purposes of heating, cooling, and auxiliary energy calculations, the 

ventilation should operate on a flat profile that is on during the occupied period 

only, with a flow rate determined by the product of the peak occupancy density 

and fresh air rate per person (both from the NCM Activity Database). The 

profile is the same for both natural and mechanical ventilation and does not 

modulate with the occupancy profile. 

Table 4: HVAC Seasonal system efficiencies in the notional building 

Servicing strategy SCoP † Cooling 

SSEER 

Auxiliary energy 

Heating with natural 

ventilation 

0.73 N/A See paragraph 45.a 

Heated with mechanical 

ventilation 

0.78 N/A See paragraph 45.b 

Fully air-conditioned 0.83 1.67 See paragraph 45.c 

Changeover mixed-mode 

with natural ventilation 

0.73 2.25 †† See paragraph 45.a 

Changeover mixed-mode 

with mechanical ventilation 

0.78 2.25 †† See paragraph 45.b 

No heating with natural 

ventilation 

N/A N/A 0 

† 

Referred to as Seasonal System Efficiency (SSEff) in iSBEM User guide. 

†† 

This SSEER includes an allowance for fan energy when the system operates, so no 

additional auxiliary energy needs to be determined beyond what is described above. 

45. The auxiliary energy per unit floor area in the notional building must be calculated 

as follows: 

a. For heated only and naturally ventilated spaces: the product of 0.61 W/m 2 and 

the annual hours of operation of the heating system from the NCM Activity 

Database. 

b. For mechanically ventilated spaces: the product of the outside air rate for the 

space, the annual hours of operation (both from the Activity Database) and the 

appropriate specific fan power from Table 5. If the zone is heated, then the 

auxiliary energy should also include the energy from paragraph 45.a. 

c. For air-conditioned spaces: the product of the annual hours of operation and 

the greater of either: 

i. The product of the fresh air rate (from the NCM Activity Database) and the 

appropriate SFP from Table 5, or 

ii. 8.5 W/m 2 . 

17

d. For spaces with mechanical extract: the product of the extract rate provided by 

the user for the actual building, the annual hours of operation (from the NCM 

Activity Database), and the appropriate SFP from Table 5. If the zone is heated 

only, mechanically ventilated, or air-conditioned, then the auxiliary energy 

should also include the energy from paragraph 45.a, 45.b, or 45.c, respectively. 

Table 5: Specific fan power for different ventilation systems in the notional building 

System type Specific fan power W/(litre/s) 

Centralised balanced mechanical ventilation 

2.0** 

system 

Zonal supply system 1.2** 

Zonal extract system serving multiple spaces, 

0.8 

i.e. fan is remote from zone 

Local extract serving a single area, i.e. fan is 

0.5 

within zone (e.g. toilet extract) 

** If the activity in the space requires the use of higher levels of filtration, e.g., High 

Efficiency Particulate Air (HEPA) filters, the specific fan power is increased by 1.0 

W/(litre/s). 

46. In the notional building: 

a. No allowance should be made for heat recovery equipment. 

b. No allowance should be made for demand-controlled ventilation. 

47. The overall system efficiency (including generation and distribution) for the water 

heating system in the notional building must be taken as 0.45, and the fuel must 

be as specified in paragraph 41. The energy demand must be taken as that 

required to raise the water temperature from 10 o C to 60 o C based on the demands 

specified in the NCM Activity Database. The Activity Database defines a daily total 

figure in litres/(m 2 .day). If users of DSMs wish to distribute this demand over the 

day, then the daily total should be distributed according to the occupancy profile. 

48. The notional building must be assumed to have no power factor correction and 

none of the adjustment factors from clause 6.1.9 in Section 6 apply. 

Installed Lighting Power Density 

49. For general lighting in the notional building: 

a. For office, storage, and industrial spaces, divide the illuminance appropriate to 

the activity in the space, as given in the NCM Activity Database, by 100, and 

then multiply by 3.75 W/m 2 per 100 Lux. This includes all spaces that 

accommodate predominantly office tasks, including classrooms, seminar 

rooms, and conference rooms, including those in schools. 

18

. For other spaces, divide the illuminance appropriate to the activity in the space, 

as given in the NCM Activity Database, by 100, and then multiply by 5.2 W/m 2 

per 100 Lux. 

50. For display lighting in the notional building, take the display lighting power density, 

in W/m 2 , appropriate to the activity in the space from the NCM Activity Database. 

51. In all cases, the duration of the lighting demand must be as per the activity 

schedule in the NCM Activity Database. 

52. It must be assumed that the general lighting in the notional building has local 

manual switching in all spaces. 

Calculation methods for the impact of controls on lighting energy demand must be 

at least as detailed as the procedures specified in the SBEM Technical Manual 18 . 

The Target Emission Rate (TER) 

53. The notional building, with the parameters as defined above, must be used as the 

basis of determining the CO2 emission Target Emission Rate (TER), irrespective of 

the calculation method used to determine the heating and cooling demands 

themselves. For the actual building, DSMs may represent HVAC systems 

explicitly, but will be required to report overall seasonal performance parameters 

as an aid to checking - see paragraph 7.c. 

54. The TER must then be calculated by adjusting the emissions of the notional 

building and reducing them by an improvement factor as specified in the equations 

in clause 6.1.7 of Section 6. The improvement factor differs depending upon 

whether a building (or part of a building) is either heated and naturally ventilated or 

heated and mechanically ventilated/ air conditioned. Accordingly, the level of 

improvement for a building which contains areas with different servicing strategies, 

IFb, is calculated by applying the relevant improvement factor, IFi, to each area of 

the building with a different servicing strategy, weighted by the CO2 emissions of 

that area from the notional building, kgCO2,i. 

Where 

( IFi 

kgCO2 

, i ) ∑ ( kgCO2 

) 

= ∑ ∗ 

i 

IF b 

, 

IFi represents the improvement factor from clause 6.1.7 of Section 6 that applies 

to each area i of the building. If the area is designed for mixed-mode operation, 

then the improvement factor for heated and naturally ventilated space must be 

used. 

kgCO2,i is the carbon dioxide emissions, in kg, from the notional building produced 

in area i, where i refers to each area of the building that has a different servicing 

strategy. 

18 Available for download from the NCM website at www.2010ncm.bre.co.uk. 

19

55. If in a certain space in the actual building, the service strategy includes mechanical 

cooling, an improvement factor of 0.9 is applied when calculating the cooling load 

for the corresponding space in the notional building. It is intended that this 

reduction in the emissions arising from the cooling component of the notional 

building will encourage the use of passive and low carbon cooling solutions. 

56. If in a certain space in the actual building, the heating fuel is grid-supplied 

electricity (whose CO2 emission factor increased from 0.422 kgCO2/kWh in 2007 

to 0.517 kgCO2/kWh in 2010), the heating load of the corresponding space in the 

notional building is adjusted by a factor which maintains the 2007 relationship of 

grid electricity to the gas/oil baselines. The adjustment factors increase the 

notional building’s CO2 emissions for heating, and consequently the TER, as 

described below: 

a. If the notional building’s heating fuel is determined to be natural gas, whose 

CO2 emission factor increased from 0.194 kgCO2/kWh in 2007 to 0.198 

kgCO2/kWh in 2010, the heating load in the notional building is multiplied by a 

factor of 1.2. This factor has been calculated using: 

(0.194x0.517)/(0.198x0.422)=1.2 

b. If the notional building’s heating fuel is determined to be oil, whose CO2 

emission factor increased from 0.265 kgCO2/kWh in 2007 to 0.297 kgCO2/kWh 

in 2010, the heating load in the notional building is multiplied by a factor of 

1.09. This factor has been calculated using: 

(0.265x0.517)/(0.297x0.422)=1.09 

57. Emissions calculations for both the actual and notional buildings must use the CO2 

emission factors shown in Table 6. 

20

Table 6: Carbon dioxide emission factors 

Fuel type 

Natural Gas 0.198 

LPG 0.245 

Biogas 0.018 

Oil 0.297 

Coal 0.35 

Anthracite 0.318 

Smokeless Fuel (inc. Coke) 0.344 

Dual Fuel Appliances (Mineral + Wood) 0.206 

Biomass 0.013 

Grid Supplied Electricity 0.517 

Grid Displaced Electricity 0.529 

Waste Heat 0.058 

Modular and Portable Buildings 

Emission factor 

kgCO2/kWh 

58. For modular and portable buildings, the TER must be adjusted as described in 

Annex 6.C of Section 6. Annex 6.C also specifies the fabric limiting standards for 

these types of buildings. 

Shell Buildings 

59. In the context of application for building warrant, a shell building is defined as a 

building where elements of the fixed building services are absent and further 

installation work will be required before the building can be occupied and used. A 

staged building warrant, covering both shell and subsequent fit out work, is not 

subject to the following process. 

60. Shell buildings are subject to the compliance check against the TER under the 

conditions specified in clause 6.1.10 of Section 6. Guidance on provisions and 

details of the limiting standards for shell and fit out buildings are specified in 

clauses 6.2.3, 6.2.4, 6.2.5, and 6.2.6 of Section 6. 

61. Assessment under standard 6.1 is required both for the shell building warrant and 

also for the subsequent fit-out works, provided a continuing requirement in this 

respect is placed upon the shell warrant. Regardless of whether or not a building 

warrant is required for fit-out work, this continuing requirement must be discharged 

before the building can be occupied (refer to clause 5.6 of the BSD Procedural 

Handbook). Assessment of the fit-out work should be made using the category 

‘other buildings’ under ‘S6 type of building’. 

62. Assessment of the shell building should show that the building, as completed, 

could meet standard 6.1. This is done by providing a completed service 

specification for each zone, identifying which services are to be installed as part to 

shell works and which are assumed to form part of a subsequent fit-out. Assumed

(uninstalled) services should be defined at zone level by identifying whether the 

zone is a fit-out area (approved software tools must allow for this identification). 

iSBEM enables this by providing a tickbox within the Geometry/Zones tab if ‘shell 

building’ is selected under ‘S6 type of building’. 

63. Energy associated to HVAC, lighting and HW systems serving 'fit-out' zones will be 

accounted for as normal in the calculation, which will assume that fit-out services 

are fully operational, designated temperatures are maintained, lighting and hot water 

provided in all zones. That means the boundary conditions between zones are 

unaffected. The calculation for the notional building is unaffected by this process. 

64. These procedures only apply to compliance with standard 6.1. EPC generation is 

still required for such a building, when fitted out. 

Extensions to the Insulation Envelope 

65. For extensions to the insulation envelope, the new building fabric should be 

designed to comply with the limiting standards specified in clause 6.2.11 of Section 

6. There are two ways to assess an extension by use of iSBEM: It is possible to 

assess the extension in isolation from the existing building, or alternatively assess 

the entire building as extended. Both these approaches are compatible with iSBEM. 

22

4 Energy Performance Certificates (EPCs). 

66. Energy Performance Certificates (EPCs) provide prospective buyers/tenants with 

information about the energy performance of a building and practical advice on 

improving performance. Cost effective recommendations for improving the energy 

performance of the building detailed on the certificate must meet the Scottish 

building regulations, be specific to the individual building and be technically 

feasible. The EPC displays the “rating” of a building in the form of the approximate 

annual Building CO2 Emission Rate (BER) in kg per m 2 of floor area per year, 

rated on a seven band scale (see clause 6.9.2 of Section 6). 

67. While an EPC is not required for permanently unconditioned buildings (i.e. 

buildings which do not use energy to condition the indoor climate and are expected 

to remain this way), it is possible to voluntarily produce EPCs for unconditioned 

buildings. Permanently unconditioned buildings are different to those which are 

currently unconditioned but are intended to be conditioned prior to occupation, and 

which should be modelled as per the guidance on shell and fit out buildings in 

Section 6. Further guidance on EPCs is provided in the BSD website 19 . 

68. The EPC ‘A to G’ scale and energy labels corresponding to values of the BER are 

displayed in, with “Carbon Neutral” being the most efficient (followed by “A+”) and 

“G” being the least efficient. This is a seven band graphical scale where a letter 

rating or letter plus rating are shown on the same band. 

69. The EPC is accompanied by a “Recommendations Report”, which contains a list of 

NCM recommendations, edited and added to by the assessor, for the improvement 

of the energy performance of the building and their respective potential impact on 

the CO2 emission rate of the building. The recommendations are grouped into the 

following sub-sections in the report: short payback (up to 15 recommendations), 

medium payback (up to 10 recommendations), long payback (up to 5 

recommendations), and other recommendations created by the assessor (up to 10 

recommendations). 

70. The EPC itself displays the top 6 of the short payback (i.e. three years or less) 

NCM recommendations. If there are user-defined or user-edited 

recommendations, then the EPC displays the top 3 NCM cost effective 

recommendations with a payback period of three years or less and up to 3 user 

recommendations with the shortest payback. 

71. The impact of the recommendations on the CO2 emission rate of the building and 

their estimated payback 20 is assessed based on the energy performance of the 

actual and notional buildings. 

19 

http://www.scotland.gov.uk/Topics/Built-Environment/Building/Building-standards/publications/pubepc 

20 

Details of the logic used for generating the NCM recommendations, their impacts, and paybacks are in 

the SBEM Technical Manual available from the NCM website at www.2010ncm.bre.co.uk. 

23

Other reference values 

Table 7: EPC scale and energy labels 

BER ≤ 0 . 0 ⇒ 

0 . 0 

7 . 5 

15 . 0 

22 . 5 

30 . 0 

37 . 5 

45 . 0 

52 . 5 

60 . 0 

70 . 0 

80 . 0 

90 . 0 

100. 

0 

CarbonNeutral 

< BER ≤ 7. 

5 ⇒ A + 

< BER ≤ 15. 

0 ⇒ A 

< BER ≤ 22. 

5 ⇒ B + 

< BER ≤ 30. 

0 ⇒ B 

< BER ≤ 37. 

5 ⇒ C + 

< BER ≤ 45. 

0 ⇒ C 

< BER ≤ 52. 

5 ⇒ D + 

< BER ≤ 60. 

0 ⇒ D 

< BER ≤ 70. 

0 ⇒ E + 

< BER ≤ 80. 

0 ⇒ E 

< BER ≤ 90. 

0 ⇒ F + 

< BER ≤ 100. 

0 ⇒ F 

< BER ⇒ G 

72. In addition to the building rating, the EPC displays two reference values as follows: 

a. The potential rating of the actual building had it been built to building 

regulations standards current at the date of issue of the EPC. 

b. The potential rating of the actual building if certain cost-effective improvements 

were applied. Assessors can use the software tool to arrive at that improved 

rating by implementing their selected cost-effective recommendations into a 

model of the building and running the calculation again. The value of the 

improved rating can then be input into the original model of the building in order 

to appear on the produced EPC. 

73. The EPC also displays other information such as, the approximate annual energy 

use of the building, in kWh/m 2 of floor area, the main heating fuel, the electricity 

source, the ventilation strategy and the main renewable energy source in the 

building, if applicable and calculated by the calculation tool. 

24

5 Input Data to Approved Tools. 

74. This section describes generally applicable approaches to data input and 

modelling strategies and applies equally to Section 6 compliance and EPCs, and 

also to the modelling of the actual and notional buildings. 

Defining internal gains and environmental conditions 

75. In order to facilitate estimating energy performance on a consistent basis, a key 

part of the NCM is a set of databases that define the activities in various types of 

space in different classes of building 21 . One of these standard activities must be 

assigned to each space in the building 22 . 

76. The NCM Activity Database provides standard occupancy, temperature set-points, 

outdoor air rates, and heat gain profiles for each type of space in the buildings, so 

that buildings with the same mix of activities will differ only in terms of their 

geometry, construction, building services and weather location (though in 

Scotland, a single weather location is identified). Thus, it is possible for the Section 

6 compliance checks and EPCs to compare buildings on the basis of their intrinsic 

potential performance, regardless of how they may actually be used in practice 

(See Chapter 6 of this guide for more details on the NCM Activity Database). 

77. If there is not an activity in the Activity Database that reasonably matches the 

intended use of a space, then this should be raised with the database managers 

(through the NCM website) and an appropriate new activity proposed. This will be 

subject to peer review prior to formal acceptance into the database. Note that it is 

not acceptable for users to define and use their own activities. Consistent and 

auditable activity schedules are an important element of the compliance and 

certification processes and so only approved activity definitions can be used for 

these purposes 23 . If a special use space is present in the actual building, and no 

appropriate activity is available in the database, it is accepted that time pressures 

may preclude waiting for the specific activity definition to be developed, peer 

reviewed and approved. In such situations, the assessor must use their technical 

expertise or seek guidance from appropriate sources in order to select the closest 

match from the approved database. 

21 

The NCM databases can be downloaded from the NCM website at http://www.2010ncm.bre.co.uk. 

22 

In a school, these activities might be teaching classrooms, science laboratories, a gymnasium, eating 

areas, food preparation, staff room, circulation spaces or toilets. The parameter values vary between 

building types, for e.g., offices in schools are not the same as those in office buildings. 

23 

Clearly designers may wish to use alternative bespoke schedules for particular design assessments, 

but these exist outside the compliance/certification framework. 

25

Constructions 

78. The thermal performance of construction elements must take account of thermal 

bridges as follows: 

a. Repeating thermal bridges must be included in the calculated plane element Uvalue 

as explained in BR 443 24 and set out in BS EN ISO 6946: 2007. 

Simulation tools that use layer by layer definitions will need to adjust the 

thicknesses of insulation layers to achieve the U-value that accounts for the 

repeating thermal bridges. 

b. Non-repeating thermal bridges, such as at junctions and around openings, as 

described in IP 1/06 25 . 

79. Available on the NCM website is the NCM Construction Database containing the 

calculated U-values, κm values, etc, and for consistency, all implementations of the 

NCM should preferably use this database. It is accepted that a required 

construction may not always exist in the NCM database. In such cases, alternative 

sources of data may be used, but the person submitting for building regulations 

approval must declare this and demonstrate how the values were derived. 

80. When using the software tool to generate an EPC for an existing building, the 

performance parameters for some constructions may not be known. In such 

situations, the parameters must be inferred, for example, using the inference 

procedure in SBEM which is defined in paragraph 95 of this document. This is an 

important aspect of ensuring consistency in energy rating calculations, and so all 

software tools must adopt these procedures. This will be checked as part of the 

approvals process. 

Low and zero carbon systems 

81. The approach described below must be followed when calculating the impact of 

on-site electrical generation for both Section 6 compliance and EPC calculations, 

as applied to non-domestic buildings: 

a. Calculate the annual electrical energy used by the building irrespective of the 

source of supply. Multiply that demand by the CO2 emission factor of gridsupplied 

electricity (Table 6). 

b. Calculate the electricity generated by the on-site system and multiply that by 

the CO2 emission factor of grid-displaced electricity (Table 6), irrespective of 

the proportion of electricity that is used on-site and how much is exported. 

c. The electricity-related CO2 emissions used to establish the building’s emission 

rate is the net figure, i.e. the result of paragraph 81.a minus the result of 

paragraph 81.b. 

24 Conventions for U value calculations, BRE, 2006. 

25 BRE IP 1/06: Assessing the Effects of Thermal Bridging at Junctions and around Openings. 

26

d. Any fuel used in generating the electricity (e.g., in a CHP 26 generator) is added 

(at its appropriate CO2 emission factor) to arrive at the total building’s CO2 

emissions. 

Weather Location 

82. In order to calculate the reaction of the building fabric and systems to the variable 

loads imposed by the external environment, the NCM needs an input of weather 

data. A standard weather set 27 has been adopted for Scotland, which must be 

used. 

Zoning Rules 

83. The way a building is subdivided into zones will impact on the energy performance 

calculations. Therefore, this guide defines zoning rules that must be applied when 

assessing a building for the purposes of Section 6 compliance or producing the 

Energy Performance Certificate. 

84. The end result of the zoning process should be a set of zones where each zone is 

distinguished from all others in contact with it by differences in one or more of the 

following: 

a. The activity attached to it. 

b. The HVAC system which serves it. 

c. The lighting system within it. 

d. The access to daylight (through windows or rooflights). 

85. To this end, the zoning process within a given floor plate is as follows: 

a. Divide the floor into separate physical areas, enclosed by physical boundaries, 

such as structural walls or other permanent elements. 

b. If any part of an area is served by a different HVAC or lighting system, create a 

separate area bounded by the extent of those services. 

c. If any part of an area has a different activity taking place in it, create a separate 

area for each activity. 

d. Attribute just one “activity” (selected from the options available for each building 

type in the NCM Activity Database) to each resulting area. If the building is 

speculative, and the activity is not fully defined, select the appropriate 

‘speculative activity’ for the relevant building type. 

26 Combined heat and power. 

27 This is the 2006 CIBSE Test Reference Year for Glasgow. See 

http://www.cibse.org/index.cfm?go=publications.view&item=332. Monthly average files have been 

created for use within SBEM. 

27

e. Divide each resulting area into “zones” receiving different amounts of daylight, 

defined by boundaries which are: 

i. At a distance of 6m from an external wall containing at least 20% glazing. 

ii. At a distance of ‘1.5 x room height’ beyond the edge of an array of rooflights 

if the area of the rooflights is at least 10% of the floor area. 

iii. If any resulting zone is less than 3m wide, absorb it within surrounding 

zones. 

iv. If any resulting zones overlap, use your discretion to allocate the overlap to 

one or more of the zones. 

f. Merge any contiguous areas which are served by the same HVAC and lighting 

systems, have the same activity within them (e.g. adjacent hotel rooms, cellular 

offices, etc.) and which have similar access to daylight, unless there is a good 

reason not to. 

g. Each zone should then have its envelopes described by the area and 

properties of each physical boundary. Where a zone boundary is virtual, e.g. 

between a daylit perimeter and parts of the building that are away or far from its 

perimeter, no envelope element should be defined. 

86. Where contiguous areas have been merged into one, then the partitions that 

separate the physical spaces must be included in the definition of the zone’s 

envelopes in order to properly represent the thermal storage impact. 

Measurement and Other Conventions 

87. In order to provide consistency of application, standard measurement conventions 

must be used. These apply to both DSMs and third party software interfaces to 

SBEM, although some parameters may only relate to the latter. These conventions 

are specified in table 8 below. 

28

Table 8: Measurement and other conventions 

Parameter Definition 

Zone Height Floor to floor height (floor to soffit for top floor), i.e. including floor void, 

ceiling void, and floor slab. Used for calculating length of wall-to-wall 

junctions, radiant and temperature gradient corrections, and air flow 

through the external envelopes due to the stack effect. 

NB: For a zone with a flat roof, the zone height would be from top of floor 

to top of roof. For a zone with a pitched roof and a flat ceiling underneath 

it, the zone height would be from top of floor to underside of soffit. For a 

zone with a sloping roof (i.e. an exposed pitched roof with no flat ceiling 

underneath it), the zone height would be from top of floor to soffit height. 

If there is a suspended floor, the zone height would be measured from the 

floor surface (rather than the slab underneath it). 

Zone Area Floor area of zone calculated using the internal horizontal dimensions 

between the internal surfaces of the external zone walls and half-way 

through the thickness of the internal zone walls. Used to multiply arearelated 

parameters in databases. 

NB: If the zone has any virtual boundaries, the area of the zone is that 

delimited by the ‘line’ created by that virtual boundary. 

(Building) Total 

Sum of zone areas. Used to check that all zones have been entered. 

Floor Area 

Envelope Area Area of vertical envelopes (walls) = h * w, where: 

h = floor to floor height (floor to soffit on top floor), i.e. including floor void, 

ceiling void, and floor slab. 

w = horizontal dimension of wall. Limits for that horizontal dimension are 

defined by the type of adjacent walls. If the adjacent wall is external, the 

limit will be the internal side of the adjacent wall. If the adjacent wall is 

internal, the limit will be half-way through its thickness. 

NB: Areas of floors, ceilings, and flat roofs are calculated in the same 

manner as the zone area. Area for an exposed pitched roof (i.e. without an 

internal horizontal ceiling) will be the inner surface area of the roof. This 

parameter is used to calculate fabric heat loss, so this is the area to which 

the U-value is applied. 

Window (or 

Rooflight) Area 

Area of the structural opening in the wall or roof, i.e. it includes the glass 

and the frame. 

Deadleg Length Length of the draw-off pipe to the outlet in the space (only used for zones 

where the water is drawn off). Used to determine the additional volume of 

water to be heated because the cold water in the dead-leg has to be 

drawn off before hot water is obtained. Assumes that the hot water system 

circulation maintains hot water up to the boundary of the zone, or that the 

pipe runs from circulation or storage vessel within the zone. 

Flat Roof Roof with a pitch of 10º or less. 

Pitched Roof Roof with a pitch greater than 10º and less than or equal to 70º. If the pitch 

is greater than 70º, the envelope should be considered a wall. 

Display Window As defined in clause 6.2.2 of the 2010 Non Domestic Technical Handbook 

(Section 6). 

Personnel Door A door to an entrance primarily for the use of people. 

Vehicle Access Door A door to an entrance primarily for the use of vehicles. 

Glazed door When doors have more than 50% glazing, then the light/solar gain 

characteristics must be included in the calculation. This is achieved by 

defining these doors as windows (otherwise, they are defined as opaque 

doors).

Activity Database 

6 NCM Databases. 

88. The NCM requires the activity definitions for a building to be defined by selection 

from a set of standardised activities. For this purpose, the NCM Activity Database 

was developed. The database contains a list of building types (see Table 9 for the 

full list of building types) and the space types (activities) that typically exist in each 

one (see Table 10 for the full list of activity). Each building type has a selection of 

the total available activity types to choose from. 

89. The NCM divides each building up into a series of zones (following the zoning 

rules in paragraphs 83 - 86), each of which may have different internal conditions 

or durations of operation. This enables the calculation to be more analytical about 

the energy consumption of a mix of uses in a particular building, rather than relying 

on a generic type such as “office” or “school”. For instance, an “office” may mean 

anything between a set of cellular offices, meeting rooms, and circulation spaces 

that are only occupied during the normal working day, and a dedicated 24-hour 

call centre. The approach of setting up multiple activity areas allows such buildings 

to be defined more correctly. 

90. In order to achieve consistency in assessing compliance and producing Energy 

Performance Certificates for non-domestic buildings, when the buildings are used 

in different actual operating patterns, a number of parameters for each of the 

activity areas are fixed for each activity and building type rather than left to the 

discretion of users. These parameters 28 are mainly: 

a. Heating and cooling temperatures and humidity set points - The heating and 

cooling set-points define the conditions which the selected HVAC system will 

be assumed to maintain for the period defined by the heating and cooling 

schedules. 

b. Lighting standards - The illuminance levels (in Lux) which need to be 

maintained in each activity area for the period defined by the lighting 

schedules. This level of illumination is then provided by the lighting system 

selected by the user. In addition to general lighting, some activities are 

assumed to have display lighting. The Lux levels, along with the user selected 

lighting system, are used to calculate the heat gains from lighting. 

c. Ventilation standards - The required fresh air rate for each activity for the 

occupied period. This value is used along with the occupancy to calculate the 

quantity of ambient air which then needs to be heated or cooled to the required 

heating or cooling set-point. Whether or not the activity will include high 

28 

The data was drawn from respected sources, such as CIBSE recommendations, supplemented and 

modified where necessary to cover activity areas not listed in such sources. 

30

pressure filtration is also defined in the database (such as commercial kitchens 

and hospital operating theatres). 

d. Occupation densities and associated internal gains - An occupancy density, 

metabolic rate and schedule of occupancy are used to calculate the internal 

heat gains from people. The percentage of the metabolic gains which are 

sensible rather than latent (released as moisture) is also taken into account. 

e. Gains from equipment - Following a similar procedure as for calculating heat 

gains from people and lighting, the database calculates the expected heat 

gains from equipment for each activity based on W/m 2 and schedules of 

activity. 

f. Internal moisture gains (in the case of swimming pools and kitchens) - The 

maximum and minimum humidity requirements for each activity. This 

information is for DSMs. 

g. Duration when these set-points, standards, occupation densities and gains are 

to be maintained. 

h. Set-back conditions for when they are not maintained - For the unoccupied 

period, the system will be assumed to maintain the space at the set-back 

temperature. 

i. Hot water demand - A hot water demand is defined for all occupied spaces. 

The hot water demand is associated with the occupied spaces rather than the 

spaces where the hot water is accessed, i.e. there is a demand for hot water 

associated with an office rather than a toilet or tea room. 

91. These data are used by the calculations for both the actual and notional buildings, 

as is the weather location. The need is to ensure that assessments on compliance 

and production of Energy Performance Certificates for non-domestic buildings are 

made on a standardised, consistent basis. For this reason, the energy and CO2 

emission calculations should not be regarded as predictions for the building in 

actual use. 

92. As part of improving consistency of application and compliance, the activities in the 

2010 NCM Activity Database have been revised. Whilst not relevant to operations 

in Scotland, users may wish to note that the list of building types is now closely 

aligned with the Town and Country Planning Use Classes in England & Wales. 

This revision should limit the choice which users have over the allocation of activity 

areas and minimise the chances that some users might attempt to “tweak” the 

selection of activities to make compliance easier to achieve. 

31

Table 9: List of building types in the Activity Database with definitions 

Building Type Description 

1 Retail and Financial/Professional 

services 

2 Restaurant and Cafes/Drinking 

Establishments and Hot Food 

takeaways 

Shops, retail warehouses, hairdressers, undertakers, 

travel and ticket agencies, post offices, pet shops, 

sandwich bars, showrooms, domestic hire shops, dry 

cleaners and funeral directors. Banks, building 

societies, estate and employment agencies, 

professional and financial services and betting offices. It 

also includes launderettes. 

For the sale of food and drink for consumption on the 

premises - restaurants, snack bars and cafes. Public 

houses, wine bars or other drinking establishments (but 

not night clubs). Also premises for the sale of hot food 

for consumption off the premises. 

3 Offices and Workshop businesses Offices, research and development, light industry 

appropriate in a residential area. 

4 General Industrial and Special 

Industrial Groups 

Use for the carrying on of an industrial process other 

than one falling within any other building type 

5 Storage or Distribution Use for storage or as a distribution centre. 

6 Hotels Hotels, boarding and guest houses where no significant 

element of care is provided 

7 Residential Institutions - Hospitals 

and Care Homes 

Residential care homes, hospitals and nursing homes. 

8 Residential Institutions - Residential 

schools 

9 Residential Institutions - Universities 

and colleges 

Residential boarding schools, residential colleges and 

training centres. These follow a schedule of work 

similar to the schools schedule (with similar working 

days, breaks and holiday periods). 

Universities and other residential campuses. These 

follow a schedule of work similar to the universities 

schedule (with similar working days, breaks and holiday 

periods). 

10 Secure Residential Institutions Use for a provision of secure residential 

accommodation, including use as a prison, young 

offenders institution, detention centre, secure training 

centre, custody centre, short term holding centre, 

secure hospital, secure local authority accommodation 

or use as a military barracks. 

11 Residential spaces Spaces within a domestic building which do not form 

part of a dwelling 29 . 

12 Non-residential Institutions - 

Community/Day Centre 

Crèches, day nurseries and day centres 

13 Non-residential Institutions - Libraries 

Museums and Galleries 

Art galleries, museums and libraries 

14 Non-residential Institutions - 

Education 

Non-residential education and training centres. 

15 Non-residential Institutions - Primary 

Health Care Building 

Non-residential clinics and health centres 

29 SBEM can be used for residential spaces only in order to assess common areas of blocks of flats 

when they are heated and conservatories or stand alone buildings with an area of 50m² or more. 

SBEM cannot be used to assess dwellings in Scotland. 

32

Building Type Description 

16 Non-residential Institutions - Crown 

and County Courts 

Law courts 

17 General Assembly and Leisure plus Cinemas, music and concert halls, bingo and dance 

Night Clubs and Theatres 

halls, swimming baths, skating rinks, gymnasiums or 

sports arenas (except for motor sports or where 

firearms are used). This type also includes night clubs 

and theatres. 

18 Others - Passenger terminals Airport, Bus, Train and Sea Port passenger terminals 

19 Others - Emergency services Includes fire stations 

20 Others -Telephone exchanges Telephone exchanges 

21 Others - Miscellaneous 24hr activities Miscellaneous 24hr activities 

22 Others - Car Parks 24 hrs Enclosed or underground car park reserved for parking 

cars with 24 hrs operation 

23 Others - Stand alone utility block Modular building that just provides shower/toilet 

facilities. 

Table 10: List of activity types in the Activity Database with definitions 30 

Activity Type Description 

1 24 hrs Consulting/treatment areas For all A&E consulting/treatment/work areas, occupied 

and conditioned 24 hours a day. 

2 Assembly areas / halls An area which can accommodate a large number of 

seated people. This could include a stage area. 

3 Auditoria Theatre auditoria spaces. 

4 Bathroom Contains a bath and/or shower and usually a basin and 

toilet. Also to be used for bathrooms for staff and 

relatives accommodation. 

5 Bedroom Bedroom 

6 Bedroom unit Guest bedroom unit including bedroom and on suite 

bathroom. Contains a bath and/or shower and usually a 

basin and toilet. 

7 Car Park Area designated for parking cars (enclosed or 

underground) 

8 Cell (police/prison) A room which accommodates one or more prisoners. 

9 Changing facilities with showers An area used for changing, containing showers. This 

activity should be assigned to the shower area and all 

associated changing areas. For areas which can be 

used to for changing but which do not contain showers, 

such as a cloak room/locker room, use the Generic 

Office Space. 

10 Circulation area (corridors and For corridors and stairways when these are separated 

stairways) 

from Office spaces, e.g. stairwells for access to other 

parts of the building. 

11 Circulation area (corridors and For all non-public corridors and stairways. For public 

stairways) - non public 

circulation spaces select Eating/drinking area. 

12 Circulation area (corridors and For restricted circulation areas such ward & department 

stairways) - non-public/restricted circulation, corridor sub-waiting, and domestic 

circulation (staff accommodation). 

30 Note that in some cases, the definition will change slightly depending on the building type. 

33


13 Classroom For areas used for teaching/seminars which are not 

lecture theatres. 

14 Common circulation areas For all common circulation areas such as corridors and 

stairways outside the dwelling. 

15 Computer lab High density desk based work space with 

correspondingly dense IT. 

16 Data Centre For data centres such as a web hosting facilities, with 

24hr high internal gains from equipment and transient 

occupancy. 

17 Diagnostic Imaging For areas which contain diagnostic imaging equipment 

(such as MRI and CT scanners, Bone Mineral 

Densitometry, Angiography, Mammography, PET, 

General Imaging, Linear Accelerator, Ultrasound). This 

category should be used for any associated plant areas 

where people work. 

18 Display and Public areas All public circulation areas where people are 

walking/sitting and where display items are exhibited / 

available normally using display lighting. 

19 Display area An area where display lighting is used to illuminate 

items with glazing onto the outside such as a shop 

window, but which is boxed/enclosed, separated from 

the main retail space. 

20 Domestic Bathroom An area specifically used for bathing/washing. Contains 

a bath and/or shower and usually a basin and toilet. 

Not to be used in Scotland. 

21 Domestic Bedroom An area primarily used for sleep. 


22 Domestic Circulation For all circulation areas within the dwelling. 


23 Domestic Dining room An area which is primarily used for eating meals. 


24 Domestic Kitchen The area within the dwelling where food is prepared. 


25 Domestic Lounge The main reception room of the home. 


26 Domestic Toilet An area containing a toilet and basin which is separate 

from the main bathroom. 


27 Dry sports hall An area where indoor sports can be played. 

28 Eating/drinking area Areas where food or drink are consumed by staff and 

visitors, e.g. canteen or office restaurant sitting areas. 

29 Fitness Studio An area used for exercising/dance, usually with high 

person density but with no machines. 

30 Fitness suite/gym An area used for exercise containing machines. 

31 Food preparation area Areas where food or drinks are prepared for staff and 

visitors, e.g. kitchen in canteen or office restaurant. 

32 Generic Check-in areas Areas designated for check in, which may contain 

conveyer belts; security check areas, which may 

include equipment such as x-ray machines; and 

baggage reclaim areas. 

34


33 Generic Office Area Areas to perform office work including offices and 

meeting rooms. It can include internal corridors 

providing access to the office spaces, tea making 

facilities or kitchenettes within the office space, areas 

for photocopiers and fax machines and staff lounges. 

34 Generic Ward For all areas containing beds which accommodate 

either single or multiple patients. It includes toilets, ward 

storage, staff accommodation, day patient 

accommodation and intensive care units. 

35 Hall/lecture theatre/assembly area An area which can accommodate a large number of 

seated people. 

36 Hydrotherapy pool hall The area in which the hydrotherapy pool is contained. 

37 Ice rink An area which contains an ice rink. 

38 Industrial process area An area for industrial process work, usually involving 

large machinery or equipment. 

39 Laboratory A facility that provides controlled conditions in which 

scientific research, experiments, and measurement may 

be performed. 

40 Laundry An area used only for washing and/or drying clothes 

using washing machines and/or tumble dryers. This is 

not for where there is an individual washing machine 

within another space (e.g., a food preparation area). 

41 Lounges All areas where passengers are walking/sitting which 

are not covered by the other space types. This includes 

departure lounge, corridors, stairways and gate 

lounges. 

42 Office and consulting areas Areas to perform management, office and 

administration work separated from standard 

customer/public areas. It can include internal corridors 

providing access to the office spaces, tea making 

facilities or kitchenettes within the office space and staff 

lounges. 

43 Operating theatre For the operating theatre suite, including anaesthetic, 

scrub & preparation rooms. 

44 Performance area (stage) For stages with dedicated lighting and equipment in 

addition to that within the remainder of the space. For 

stages within other activity areas which do not have 

specific lighting or additional electrical equipment, do 

not define these as separate spaces. 

45 Physiotherapy Studio For all physiotherapy areas, e.g., Fitness Suite/Gym, 

activity area, Cardiac stress test area. 

46 Plant room Areas containing the main HVAC equipment for the 

building e.g., boilers/air conditioning plant. 

47 Post Mortem Facility Post-Mortem Facility (including Observation room and 

body preparation area). 

48 Public circulation areas All public circulation areas such as a foyer. For non 

public spaces use "Circulation areas (corridors and 

stairways) - non public" 

49 Reception The area in a building which is used for entry from the 

outside, from other building storeys or in general waiting 

areas containing a reception desk. 

50 Residents common rooms TV lounges and other common spaces for use of 

residents. It may contain some hot drink facilities. 

35


51 Residents kitchen Common area kitchens used by residents, e.g. in 

residents' halls. 

52 Sales area - chilled A sales area designed to accommodate a considerable 

quantity of fridges/freezers such as a supermarket or 

food hall. 

53 Sales area - electrical Sales areas designed to accommodate considerable 

electrical equipment loads such as lighting sales areas 

and IT/TV/Hi-Fi sales areas. 

54 Sales area - general All Sales areas which do not have a large concentration 

of fridges/freezers or electrical appliances. 

55 Server Room For areas such as computer server spaces with 24hr 

low-medium internal gains from equipment and 

transient occupancy. For an area with 24hrs high gains 

from equipment, use the 'Data Centre' activity. 

56 Storage area Areas for un-chilled storage with low transient 

occupancy. Equip = 2; Heat Set Point = 20; Cool Set 

Point = 23 

57 Storage area - chilled A storage area containing items which need to be 

chilled. The area itself can be conditioned. Lux = 100; 

Equip = 25; Heat Set Point = 13; Cool Set Point = 25 

58 Storage area - cold room (

Construction and Glazing Databases 

93. The user can specify the U-value and thermal mass information for a particular 

wall, roof, or floor for which the construction is accurately known. Where the 

construction is less precisely known, the user can make use of the NCM 

Construction and Glazing Databases. These databases contain a library of 

opaque constructions (for walls, roofs, floors and doors), glazing, and frames (for 

windows and rooflights) covering different regulation periods and different generic 

types of construction. 

94. The user may access a particular construction directly from the library by selecting 

first the generic type of construction and then selecting the particular construction 

which appears to match most closely the actual construction. Once the user has 

selected the construction, the database provides a U-value and thermal mass and, 

in the case of glazing, solar factors, and these values are then fed directly into the 

calculation. 

95. For cases where the user has only minimal information, the interface to SBEM has 

an inference procedure. When using the inference procedure, the user supplies 

basic data such as the sector (building use), the building regulations that were in 

use at the time of construction and a description of the generic type of 

construction. The type of construction which most closely matches the description 

identified in the inference will be selected and used to provide the U-value and 

thermal mass value used in the calculation. 

Table 11: Scottish opaque constructions in the NCM Construction Database 

ID Category Construction Name 

86 Curtain wall Curtain wall (SCO) 2002- 

2006 

195 Solid ground floor Solid ground floor (SCO) 

2002-2006 

251 Pitched roof, 

insulation at rafters 

295 Cavity wall (partial 

fill) 

296 Non-structural wall 

(metal) cladding 

system 


fill) 

Pitched roof, insul. at 

rafters (SCO) pre-1975 

Cavity wall (SCO) 

2002-2006 

Metal cladding wall 

(SCO) 2002-2006 

Cavity wall (SCO) 2007 

Section 6 (gas heating) 

364 Solid (masonry) wall Solid wall (SCO) 2002 

Part J 

369 Weatherboard or 

rainscreen cladding 

Weatherboard, tile-hung 

(SCO) 2002 Part J 

419 Vehicle access door Vehicle access door 

(SCO) 2007 Section 6 




(SCO) pre-1997 

37 

U-value 

[W/m 2 K] 

κm1 

[kJ/m 2 K] 

κm2 

[kJ/m 2 K] 

1.2 4 4 NO 

0.25 36 36 NO 

0.25 12 12 NO 

0.3 11.7 129 NO 

0.3 7 7 YES 

0.25 11.7 129 NO 

0.3 54 180 NO 

0.3 11.7 11.7 NO 

1.5 4.93 4.93 NO 

1.5 4.93 4.93 NO 

5.7 1.76 1.76 NO 

Metalcladding




455 Suspended floor Exposed floor (SCO) 

1997 Part J 


2002 Section 6 



458 Timber frame wall Timber frame wall (SCO) 

1997 Part J (S) 


2002 Part J 




1991 Part J 

502 Curtain wall Curtain wall (SCO) 2007 


503 Flat roof Flat roof (SCO) 2007 


504 Non-structural roof 


system 



system 


horizontal insulation 

Metal cladding roof 




Pitched roof (SCO) 2007 

Section 6 

507 Solid (masonry) wall Solid wall (SCO) 2007 

Section 6 


2007 Section 6: 

509 Cavity wall (clear) Clear cavity wall (SCO) 

pre-1975 


1975-1981 


fill) 


fill) 


fill) 









Cavity wall (SCO) 1982- 

1990 


1996 


2001 

Pitched roof (SCO) pre- 

1975 

Pitched roof (SCO) 1975- 

1981 


1990 


1996 

38 

U-value κm1 κm2 Metal- 

[W/m 2 K] [kJ/m 2 K] [kJ/m 2 K] cladding 

1.5 4.93 4.93 NO 

0.45 15 15 NO 

0.25 15 15 NO 

0.22 15 15 NO 

0.45 12 12 NO 

0.3 12 12 NO 

0.3 12 12 NO 

0.45 12 12 NO 

1.2 4 4 NO 

0.16 50.9 190.9 NO 

0.25 7 7 YES 

0.25 1.4 1.4 YES 

0.13 12 12 NO 

0.25 54 180 NO 

0.22 36 60 NO 

2.4 47.5 173.5 NO 

1 47.5 173.5 NO 

0.6 47.5 173.5 NO 

0.45 42.84 142.8 NO 

0.45 42.84 142.8 NO 

1.14 12 12 NO 

0.6 12 12 NO 

0.45 12 12 NO 

0.25 12 12 NO





2001 



0.25 12 12 NO 

519 Solid ground floor Ground floor (SCO) pre- 

1975 

1.14 22.5 92.5 NO 

520 Suspended floor Suspended ground floor 

(SCO) 1975-1981 

1 22.5 92.5 NO 


(SCO) 1982-1990 

0.6 22.5 22.5 NO 


(SCO) 1991-1996 

0.45 22.5 22.5 NO 


(SCO) 1997-2001 

0.45 6.75 6.75 NO 

524 Flat roof Flat roof (SCO) pre-1975 1.14 8.55 11.17 NO 

525 Flat roof Flat roof (SCO) 1975- 

1981 

0.6 8.55 11.17 NO 


1990 

0.45 8.55 8.55 NO 


1996 

0.45 12.45 12.45 NO 


2001 

0.45 50.9 190.9 NO 


2006 

0.45 72 240 NO 














rafters (SCO) 1975-1981 










2006 

536 Suspended floor Semi-exposed floor 

(SCO) 1982-1990 


(SCO) 1991-1996 


(SCO) 1997-2001 


fill) 


fill) 


fill) 

Semi-exposed wall 

(SCO) 1982-1990 


(SCO) 1991-1996 


(SCO) 1997-2001 

542 Solid (masonry) wall Solid wall (SCO) 1991- 

1996 

39 

0.6 12 12 NO 

0.45 12 12 NO 

0.45 12 12 NO 

0.45 12 12 NO 

0.25 12 12 NO 

0.16 12 12 NO 

0.7 22.5 22.5 NO 

0.6 22.5 22.5 NO 

0.6 6.75 6.75 NO 

0.7 47.5 173.5 NO 

0.6 42.84 142.8 NO 

0.6 42.84 142.8 NO 

0.45 54 180 NO



2001 



system 



system 


(SCO) 1991-1996 


(SCO) 1997-2001 


1996 


2001 


1982-1990 


1991-1996 


1997-2001 


2002-2006 




1990 


1981 



system 



system 



system 











563 Precast concrete 

panels 


panels 


(SCO) 1982-1990 


(SCO) 1975-1981 




(SCO) 1975-1981 


(SCO) 1982-1990 


(SCO) 1991-1996 


(SCO) 1997-2001 



Precast concrete panels 

(SCO) 1991-2001 


(SCO) 1982-1990 

40 



0.45 54 180 NO 

0.45 7 7 YES 

0.45 7 7 YES 

2.2 4 4 NO 

1.7 4 4 NO 

0.6 42.84 142.8 NO 

0.45 42.84 142.8 NO 

0.45 42.84 142.8 NO 

0.3 42.84 142.8 NO 

0.25 42.84 142.8 NO 

0.6 54 180 NO 

1 54 146.7 NO 

0.6 7 7 YES 

1 7 7 YES 

1.6 7 7 YES 

1 11.7 11.7 NO 

0.6 11.7 11.7 NO 

0.45 11.7 11.7 NO 

0.45 11.7 11.7 NO 

0.25 11.7 11.7 NO 

0.45 54 180 NO 

0.6 54 180 NO



panels 


panels 



system 



system 



system 



system 



system 




(SCO) 2002-2006 




(SCO) 1975-1981 


(SCO) 1982-1990 


(SCO) 1991-2001 


(SCO) 2002-2006 


(SCO) 2002-2006 




1992-2001 

Table 12: Scottish transparent constructions in the NCM Glazing Database 

ID Category NAME 



1 57.7 115.3 NO 

0.3 54 180 NO 

1.14 7 7 YES 

0.6 7 7 YES 

0.45 7 7 YES 

0.45 7 7 YES 

0.45 7 7 YES 

0.25 22.5 22.5 NO 

0.58 22.5 22.5 NO 

0.45 93.75 312.5 NO 

U-value 

[W/m 2 K] 

Light Transmittance 

260 Uncoated, clear Single glazing (SCO) 1966-2006 5.7 0.9 0.85 

385 Uncoated, clear Double glazing (SCO) 1975-1981 2.8 0.8 0.76 




389 Reflectance, Double glazing (SCO) 2002-2006 2 0.8 0.72 

low-emissivity (non-metal frame) 

390 Uncoated, clear Triple glazing (SCO) 2002-2006 

(non-metal frame) 

2 0.7 0.68 

394 Uncoated, clear Double glazing (SCO) pre-1975 2.8 0.8 0.76 

396 Uncoated, clear Triple glazing (SCO) 1997-2001 2.6 0.7 0.68 

397 Reflectance, Double glazing (SCO) 2002-2006 2.2 0.8 0.72 

low-emissivity (metal frame) 

398 Uncoated, clear Triple glazing (SCO) 2002-2006 

(metal frame) 

2.2 0.7 0.68 

41 

Solar Transmittance

7 Suitability of Calculation Method. 

96. Selection of the software tool to be used for a particular project will depend on a 

number of issues. These issues may apply to any software used for these 

purposes, not only to the use of iSBEM 31 /SBEM. 

Availability of Tools and Competence of Users 

97. First, the choice of software tool will depend on whether the tools that are 

available are within the competence of the users – ideally the users have 

successfully undertaken training on use of the chosen tool and have further 

practical experience of its use. Formal accreditation in the use of the tool, whilst 

not essential, is beneficial. It may be that the user has already used one of the 

DSM tools or a CAD 32 package that interfaces with one of the software tools for 

design work, so that the bulk of the input has already been undertaken; this will 

mean that it is preferable to continue to use the tool that the project has already 

been started on. 

98. Where the project requires that the software should be used outside the standard 

scenarios, for instance inputting a system that is not on the standard drop-down 

menus, it is important that the user should understand and be competent to 

extend the software in such ways. The user should also be prepared to document 

and justify any extraordinary uses of the software to an auditor or verifier in 

relation to compliance issues. 

99. It is important that there should be consistency in the rating of similar buildings, 

otherwise the credibility of the rating procedure is undermined. When software 

tools are used and assessors follow a standard set of conventions to minimise 

differences that may arise from interpretation, it should be possible to ensure that 

consistent results are obtained. On the other hand, using software that does not 

have such conventions governing its use may allow inconsistencies between 

assessors. Consistency may diminish if the simulation depends on user 

interpretation to set appropriate inputs. 

The Complexity of the Building and its Services 

100. The more complex a building and its building services, the greater the possibility 

that it may not be simulated accurately by a user. This is because data entry may 

depend on the vigilance and competence of the user to enter all necessary 

parameters reliably, and whether any checks on this can be made using the 

chosen software (e.g. if it produces a graphical representation to compare with the 

actual building). 

31 Interface to SBEM. 

32 Computer-Aided Design. 

42

101. It may also be that more complex building configurations and HVAC systems 

cannot be mapped onto the features and system descriptions listed directly in the 

software. In this case, either the software may be unsuitable to model this building 

or systems, or alternatively, it may be possible to develop a workaround that 

allows novel configurations to be entered in terms of features that are available in 

the software (see paragraph 104 below). 

Whether Workarounds are Available 

102. Where features that are not listed amongst the options in the software are to be 

simulated, the choice of software will depend on whether “official” workarounds 

that define those features in terms of parameters that the user can access have 

been developed. Software providers should inform users of any limitations of their 

software to model any aspects of the energy performance of buildings. They 

should also inform of acceptable workarounds to overcome these limitations. This 

information, consistently provided by all software vendors and frequently updated, 

should facilitate the appropriate choice of software tool to be made. 

103. If no recognised and verifiable workaround exists, the choice of software will be 

limited to those tools which can model the proposed building and its features 

directly. 

104. It is not feasible to prescribe a definitive, exhaustive list of workarounds in iSBEM. 

Practical workarounds are developed and added to the FAQ 33 page of the NCM 

website as and when the need for them arises due to common requests from 

users. 

Limitations of all Software Tools 

105. Ultimately, there might be a point at which it would have to be decided that the 

calculation provided by a given software tool cannot give credit for a particular 

unlisted feature, either directly or via a workaround. This decision will itself depend 

on whether the evaluation of the unlisted features depends on the software’s 

ability to simulate dynamic thermal interaction between the people, equipment and 

air inside the building, the building elements and building services, and the 

external environment, or whether this dynamic interaction can be simulated on a 

representative building or system and the results used to adjust a steady state 

simulation. 

106. Also, there will be features which cannot be simulated by any of the tools directly 

or via recognised and verifiable workarounds. Users should report such 

circumstances to BSD, who may consider if it is worth commissioning software 

providers to develop workarounds or new software capabilities to simulate such 

features. 

33 Frequently Asked Questions. http://www.ncm.bre.co.uk/faqs.jsp 

43

107. At the moment, features that are not directly available in SBEM include: 

i. automatic blind control, 

ii. external shading in the plane of the window, 

iii. atria where there is ventilation driven by the stack effect, and 

iv. transfer of daylight between internal zones. 

Users of the Software 

108. It is the responsibility of the users of the software tools to be adequately informed 

on whether the tool they are using can either directly assess all the features that 

affect the energy performance of the building, or include acceptable workarounds 

for the features that cannot be directly modelled. According to this, users are 

expected to make a decision on the suitability of using the software tool to model a 

particular building. 

44

National Calculation Methodology (NCM) - Scottish Government

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