00234 Tomaž Pazlar - Timber Design Society

ASSESSMENT AND REHABILITATION OF SLOVENIAN
CULTURAL HERITAGE – CASE STUDIES
Jelena Srpčič 1 , Tomaž Pazlar 2
ABSTRACT: Inspection, assessment of residual load bearing capacities of historic timber structures, as well as
proposals for their rehabilitation, are important activities performed at the Section for Timber Structures at Slovenian
National Building and Civil Engineering Institute (ZAG, Ljubljana). For this purpose a visual inspection, combined by
semi-destructive testing is mainly used. After assessing the general condition of structures, the measures for further use
are often required. This paper presents assessments of timber roof and floor structures in typical buildings characterized
as Slovenian cultural heritage together with proposed rehabilitation measures and their successful implementation.
KEYWORDS: timber structures, assessment, typical damages, residual load bearing capacity, rehabilitation measures
1 INTRODUCTION 123
The assessment of deteriorated timber structure should
give information whether it is from structural point of
view possible to preserve existing structure or it should
be decommissioned completely. In the last 20 years
Section for Timber Structures at Slovenian National
Building and Civil Engineering Institute assessed several
historic timber structures. On the basis of visual
inspection, combined with simple semi-destructive
methods (core drilling, tapping) health assessments of
several structures were performed. In some cases heavy
deterioration of timber has been observed, some
structures were sound enough to stay incorporated, and
in some cases rehabilitation measures were necessary.
The second problem observed was non-adequate load
bearing capacity of floor structures for intended use
therefore also strengthening measures have to be
proposed.
building with floor area of 700 m 2 consists of ground
floor, two storeys and high attics which have not been in
use [1].
The building was at first used as a monastery, then as
barracks (1784 – 1927) and at the end as an apartment
building. Although several “ad hoc” renovations were
performed, the building was visually in very bad
condition, mainly due to the poor maintenance,
especially when the building was used as barracks and
an apartment building.
After very long period of discussions it was decided that
the building as a historic monument has to be preserved.
Although the building was in quite bad shape, especially
wooden structures, the wish of the architects was to
preserve the original structures as much as possible and
to incorporate them into a contemporary structure.
2 CASE STUDIES
2.1 ROOF AND FLOOR STRUCTURES OF
MINORITE MONASTERY IN MARIBOR
2.1.1 About the building
The origins of Minorite monastery in Maribor date in
13 th century. The majority of monastery was renovated
in the baroque style in 18 th century. Three storey
1 Jelena Srpčič, Slovenian National Building and Civil
Engineering Institute, Dimičeva 12, 1000 Ljubljana, Slovenia,
Email: jelena.srpcic@zag.si
2 Tomaž Pazlar, Slovenian National Building and Civil
Engineering Institute, Dimičeva 12, 1000 Ljubljana, Slovenia,
Email: tomaz.pazlar@zag.si
Figure 1: West wing of Minorite monastery during the
renovation

2.1.2 Timber structures
The roof structures in all wings are symmetric and nonsymmetric
trapezoid suspended frames lying on the outer
brick walls. The main structural frames on distances 4 –
5 m carry ridge poles, rafters, and purloins. Clay roof
tiles are used.
There are two types of floor structures: above the first
floor mainly massive timber floors are installed with
joists adjacent one to another. Under the attics some
floors are massive and some are hollow (distances
between joists are ca. 0.8 – 1.0 m), all closed at bottom
and top with planks).
Figure 3: Deteriorated part of the roof in the gutter
Complete replacement of roof structure in SE part of the
building was proposed due to the heavy damage of
majority of structural elements.
Figure 2: Inspection of attics
2.1.3 Assessment of structures
Timber roof and floor structures, dated from 19 th
century, were checked twice: whereas the first inspection
performed by consultant company demanded complete
decommissioning of the roof, the second inspection,
described here, confirmed that a great deal of timber
structures were sound enough to be preserved [2].
2.1.4 Roof structures
When checking the roof structure we focussed to the
points where deterioration is expected: supports, roof–
valley elements, gutters, etc. Special attention was also
put on signs of biological attack (presence of mould or
wooden dust which indicates an attack of wood fungi
and insects).
Due to the high level of deterioration practically all
elements of roof structure were checked in details. The
most problematic parts of the structure were found on
spots where long term wetting was present. Wetting was
caused primarily by leaking at bad details at the gutters
and at bad connections of roof planes. In these parts
combined attack of fungi and wood insects caused
substantial deterioration of wood, sometimes even the
total loss of strength.
One of the most problematic elements was the main
beam with 12 m span in the SE part (called tower) which
was completely destroyed due to the attack of wood
destroying fungi. Rearrangement of load to other roof
elements caused substantial deformation of whole
structure visible also from the outside of the building.
Figure 4: Destroyed lower chord of the main frame
Some elements – also in the dry surroundings – were
heavily damaged due to insect attack. Damage was
mainly caused by the “house capricorn” (Hylotrupes
bajulus).
Figure 5: Insects attack

The roof structures in other parts of the building were in
relatively good condition. Therefore it was proposed that
the sound structural elements can be preserved.
2.1.5 Floor structures
In the attics some of the hollow floors were completely
deteriorated. The damage was visible also from the
rooms below. Some joists were completely destroyed on
supports and already temporary supported.
Figure 6: Sound structures can be preserved
Detailed description of elements which can be preserved
and elements which should be replaced was included in
the inspection report. Assessment conclusions were also
confirmed in the construction process which closely
followed the inspection report.
Figure 9: Temporary supported deteriorated floor joist
Figure 10: Detail – damaged floor joist
Figure 7: Roof structure after uncovering
Heavy damage on massive timber floors was caused
mainly by the brown rot.
Figure 8: Sound timber and the wood dowel in the ridge
Figure 11: Massive floors damaged by the brown rot

The stages of deterioration of massive timber elements in
the second floor differed: in some areas only surface was
affected whereas in some corners practically the whole
effective height of beams was damaged. The contractors
decided to leave the timber floors installed. As floors did
not have enough load-bearing capacity, the composite
concrete deck was additionally installed.
2.1.6 Today’s use of building
Renovation of Minorite monastery was finished in 2009.
Today, the building is used as a puppet theatre.
Figure 15: Renovated building is used as a puppet
theatre
Figure 12: Surface of massive floor in the second floor
High attics with visible preserved roof elements are
hosting workshops for dressing stage scenery and school
for puppet performers.
Figure 13: Strengtheing timber floor by concrete slab
Figure 16: New design of the attics premises
Figure 14: Detail: connecting dowels
Figure 17: Visible roof elements

2.2 MASSIVE TIMBER FLOOR IN MANSION
“NASKOV DVOREC” IN MARIBOR
2.2.1 About the building
Mansion “Naskov dvorec” is one of the most important
bourgeois houses in Maribor. Its core dates from 14 th
century. Most parts of the building were constructed in
17 th century and then renovated in a late Baroque style.
In 18 th and 19 th century several renovations took place
which gave the building today’s dimensions.
Walls and arch floors in some parts of the building are
made of brick, whereas the most of floors are made of
massive timber.
massive brick wall substructure elements. Joists were
visible because planks on the top were already removed.
Figure 20: Upper side of massive floors in the attics
Visual overview of floor joists combined with core
drilling revealed typical traces of wood fungi and insects
attack. Most of the damage was caused by the insects,
mainly the old-house borer (Hylotrupes bajulus L.)
whereas the damage caused by fungi was local.
Figure 18: The building during the renovation
Presented mansion is – similar as already presented
monastery – considered as urban cultural heritage and
protected by monument–protection law. Therefore the
investor, the municipality of Maribor, was committed to
preserve as much structure as possible, mainly because
of the frescos discovered under the limed ceiling.
Figure 21: Floor joists attacked by insects
Figure 19: Frescoes under the lime ceiling
2.2.2 Assessment of floor structures
The assessment of timber floors in the attics was
performed during undergoing renovation [3]. The
majority of floor structures were massive timber floors.
Hollow timber floors were installed only in some parts
of the building. The orientation of elements depends on
Figure 22: Estimating the depth of damaged wood by
core drilling

2.2.3 Measures for future use
The assessment proved that the majority of massive
timber floor elements can be preserved. However,
several re-strengthening actions were foreseen. The
deteriorated part of massive timber floor elements (or
whole elements) should be replaced with impregnated
new elements. The most damaged top layer (2 – 3 cm) of
all massive timber elements should be manually
removed, and the surface should be impregnated with
insecticide. After impregnation a layer of PE foil should
be installed to prevent wetting of the timber elements.
Additional separation layer should also be installed
(expanded polystyrene for example) in order to prevent
the direct transfer of loads from concrete slab to massive
timber floor elements. This solution will enable
preservation of valuable old frescoes.
It has also been recommended that concrete with low
water cement ratio should be used. In order to assure
durability of timber members porous materials should be
used in renovation of ceilings.
2.3 HOLLOW TIMBER FLOORS IN TOWN
HALL IN KOČEVJE
2.3.1 About the building
Town hall in Kočevje was built between 1889 and 1899.
Its original purpose was a private girl’s school, led by
the nuns (St. Mary home). In the World War I building
was used as a hospital. Today it is a town hall hosting
the offices of municipality, public administration and the
country court.
The building with floor area of 940 m 2 has a ground
floor, two storeys and high attics which are also in use.
All walls are made from masonry. The floor structures
above the ground floor are mason arches. Above the
upper storeys floors are made from timber. Except
general floor plans and cross sections we were not able
to obtain any documents describing timber floors or any
other construction details.
Figure 25: Town hall Kočevje
Figure 23: Old frescoes are going to be preserved
The renovated mansion shall be in future used as a
cultural centre and as a gallery. Today it is used as an
administrative centre for the cultural program “Maribor
2012 - European Capital of culture”.
2.3.2 Assessment of floor structures
Subjects of assessment were the hollow timber floors in
the first and the second floor [4]. Both opening spots (1 x
1.5 m) were located near supports on outer walls.
Figure 26: Opening spots
Figure 24: Building is now a centre of European Capital
of Culture 2012
The structure in the first floor was in very good
condition. The gravel/sand layer was completely dry.
Timber was not deteriorated; only some cracks were
identified in joists.

2.3.3 Load bearing capacity of floor structures
Since there were no records about the floor structures,
the dimensions of floor elements were evaluated from
the opening spots.
Figure 27: Dry and sound joist in the first floor
Gravel/sand layer on the second floor was also dry, but
on the joists some consequences of wetting were visible
(fungi, the brown rot).
Figure 28: Wet joists in the second floor
Figure 29: Measuring the dimensions of floor elements
2.3.4 Ultimate limit state and serviceability limit
state
The load bearing capacity and deflections were checked
according to EN 1995-1-1:2005 using proposed values
from EN 1991-1-1:2004. On the basis of measured floor
elements it has been assessed that the permanent load of
2.1 kN/m’ (2.7 kN/m’ in second floor) has to be taken
into account. The effective beam cross section of 20 x 24
cm and mechanical characteristics for timber strength
class C24 were used in calculation. A simple supported
beam with 6 m span was used as structural model.
As building is used for offices, the imposed load for
Category B (characteristic value of uniformly distributed
load 3.0 kN/m 2 ) is taken into account. The design values
of actions, design resistances and their ratios are
presented in Table 1.
Table 1: Ultimate limit state
1 st floor
2 nd floor
Design
action
bending
Design
resistance
Ratio
Design
action
shear
Design
resistance
[kNm] [kNm] [kN] [kN]
Self Weight 13.3 21.3 0.6 8.7 59.1 0.2
Self Weight + Imposed Load 30.8 28.4 1.1 20.1 78.8 0.3
Self Weight 16.8 21.3 0.8 11.0 59.1 0.2
Self Weight + Imposed Load 33.7 28.4 1.2 22.0 78.8 0.3
Ratio
Presented ratios indicate that in both floors design
actions exceed design resistances. The results do not
include masonry partition walls which are sometimes
installed above the beams and sometimes above top
planks of floor structure. If partition walls are taken into
account, the ratio design action/design resistance
increases to 3.7 (or 3.4 in the second floor).
The serviceability limit state proves to be more
problematic in both cases. When the regular load is
considered, obtained ratios for instant load and final
stage exceed allowable values (see Table 2). When the
masonry partition walls are taken into account, the finite
ratios increase up to 5.3 (or 4.2 accordingly).

Table 2: Serviceably limit state
1 st floor
2 nd floor
Displacement
instant
Allowed
displacement
Ratio Displacement
finite
Allowed
displacement
[mm] [mm] [mm] [mm]
Distributed load 33 1.6 53 1.3
Ratio
Point load 24
20
1.2 38
41
0.9
Distributed load 37 18 58 1.4
Point load 28
1.4 44
1.1
2.3.5 Proposed measures
Although we did not identify any deteriorated part of the
structure, the assessed hollow timber floors do not meet
current standard requirements. However we estimate that
the structure can be preserved if self weight is decreased
– the depth of sand/gravel layer should be reduced. More
probable solution is the complete removal of sand/gravel
layer and installation of new lighter sound isolation
material. Masonry partition walls can not be preserved.
They should be replaced with lighter structure (e.g. from
gypsum plaster boards).
3 ASSESSMENTS FINDINGS
Three typical assessments of timber structures,
performed by ZAG, and proposed measures for their
rehabilitation were presented in this paper. Although all
buildings were historic buildings, outcomes of
assessments and renovation measures were different [5].
Timber structures in Minorite monastery were in some
parts heavily deteriorated. Therefore many roof elements
and the whole upper floor structure were proposed to be
replaced. The floor structure above the lower floor had to
be strengthened.
Floor structures in Naskov dvorec on which valuable
frescoes have been discovered are proposed to stay
installed. To ensure sufficient load bearing capacity the
installation of new concrete floor structure, separated
from the original floor, was proposed.
Floors of town hall Kočevje were in quite good
condition (especially in the first floor), but their load
bearing capacity according to Eurocode has been not
sufficient for intended use. Therefore some rehabilitation
measures were proposed (reducing or replacing the
heavy sand layer, removing masonry partition walls).
4 CONCLUSIONS
After many years of practice we can propose that
assessments of old timber structures should include
several items: the most important are recognition of
wood degrading agents, determination of deterioration
level and at the end proposition of the measures for
structural rehabilitation. The good assessment demands
wide knowledge of construction solutions, needed for the
partial replacements of load bearing structures. In this
case the possibility of the supporting the remaining parts
of the structure should be explored.
Presented methods of assessment are considered as a
non-destructive and – in the case of floors – semi–
destructive visual inspection. A complete information
about floor structure can be obtained when opening the
hollow timber floor. However the procedure is time
consuming and relatively small part of structure is
checked. To improve the inspection methods the
endoscope camera can aslo be used. Unfortunately this
method can be sucessfuly used only in cases where
visual evaluation of floor structure is required. When
dimensions have to be evaluated, the opening of floor
structure is recomended as accuracy of measurements
with endoscope camera is not always satisfying.
REFERENCES
[1] Srpčič J.: Biological deterioration of historical
wooden roof and floor structures and their
renovation, International conference on Wood
Science for Preservation of Cultural Heritage:
Mechanical and Biological Factors, Braga, 2008.
[2] Srpčič J.: Report on inspection and assessment of
timber roof and floor structures in the Minorite
monastery in Maribor, Report P 105/08-640-1,
Slovenian National Building and Civil Engineering
Institute (ZAG, Ljubljana), 2008 (in Slovenian
language).
[3] Srpčič J. Report on inspection, assessment and
proposed re-strengthening measures of the massive
floor structures in Naskov dvorec in Maribor,
Report P 294/09-640-1, ZAG, Ljubljana, 2009 (in
Slovenian language.)
[4] Pazlar T., Srpčič J.: Report on inspection,
assessment and calculation of the load-bearing
capacity of the floor structures in the Town hall in
Kočevje, Report P 258/10-640-1, ZAG, Ljubljana,
2010 (in Slovenian language).
[5] Srpčič J., Pazlar T.: Some examples of the
assessment of Slovenian historical timber structures,
International Conference on Structural Health
Assessment of Timber Structures, SHATIS 11,
Lisbon, 2011.