Book - School of Science and Technology

30 The building in wintermost commonly used as infill material or as an inner skin protected from the weather.When used with flat roofs, insulants are prone to absorb condensation and hence a vapourseal or some means of venting is required: recent building methods use a form ofconstruction known as the inverted or `upside down' roof in which the insulating membraneis placed on top of the structure below the water-proofing layer. Nevertheless, it isfrequently possible, by the selection of the right materials and techniques, to achieve ahigh degree of insulation for little or no overall cost.Table 2.3 provides details of a range of common types of insulating material.LegislationViewed in the light of today (and tomorrow) it may seem strange that it was about 25years ago that the influence of Building Regulations began to have a direct and substantialbearing upon those aspects of construction which affect the thermal behaviour of abuilding. The Health and Safety at Work Act (1974), Part III, provided power wherebythe Secretary of State may make Regulations with respect to the design and constructionof (all) buildings for the purpose of `furthering the conservation of fuel and power'. Thiswas a considerable advance in that previous powers existed only under the ThermalInsulation (Industrial Buildings) Act (1957), which provided for a mediocre standard ofinsulation to factory roofs, and under the Public Health Acts which were unrelated toenergy conservation and limited to the construction of dwellings.The Building Regulations of 1976 (Second Amendment) applied also to dwellingsalone and it was not until July 1979 that the Regulations of 1978 (First Amendment)extended that influence to embrace all other categories of building. A later issue of 1985,makes specific reference to a requirement from Part L of Schedule 1 to the effect that`Reasonable provision shall be made for the conservation of fuel and power in dwellings andother buildings whose floor area exceeds 30 m 2 .' The detailed requirements wererevised in 1991±2, again in 1995, and a further comprehensive amendment is scheduledfor 2002.Building Regulations 1991 Part L (amended 1995)This revision followed the established pattern of setting out criteria to limit the heatloss through the building fabric. This was achieved through the definition of maximumU-values for each building element (wall, roof, floor and opening) and standardarea allowances for openings (windows, doors and rooflights). These so-called elementalstandards provide a reference heat loss condition; designers can vary the individualelemental values, provided the rate of heat loss from the building as designed is no greaterthan from a building of the same size and shape that meets the elemental criteria. As anadditional option, the designer can use an energy calculation model to show that the designas a whole will consume no more energy than an equivalent meeting the elementalcriteria. The calculation model to be used for dwellings is the Standard AssessmentProcedure (SAP).The method of calculating U-values was also changed to take account of the effect ofrepeating thermal bridges. Other potential thermal bridges such as around openings werealso highlighted and example lintel, jamb and sill designs provided that would givesatisfactory performance. In a similar way, the need to limit infiltration was identifiedand simplified details shown by way of example.