Facade Refurbishment – Improving the Energy Performance of the Existing Building Stock in Belgrade

Natasa Cukovic-Ignjatovic and Dusan Ignjatovic

Faculty of Architecture, University of Belgrade, Belgrade, Serbia and Montenegro

ABSTRACT: Urban tissue of Belgrade comprises rather large building stock, mainly dwellings with poor performance regarding energy and some aspects of human comfort. This paper is trying to identify the most efficient strategy for improving the energy balance citywise by focusing on specific building types that are the most suitable for energy rehabilitation. Certain interventions that are most likely to occur in present conditions are analysed and compared.

Conference Topic: 6 Recycled architecture (re-use, upgrading and rehabilitation of buildings) Keywords: facade, energy, modification

INTRODUCTION erection and milestone years that significantly influenced the building practice in Belgrade. Urban tissue of Belgrade comprises rather large 2.1 Buildings Dated Before 1941. building stock, mainly dwellings with poor Some 15% of present building stock1 was performance regarding energy and some aspects of constructed before World War II and it could not be human comfort. Throughout last 50-60 years, the considered as representative for numerous reasons permanent migrations caused constant demand for such as: housing that has significantly shaped the present rather modest number of apartments image of the city. This paper tends to identify the great variety of building types most commonly encountered problems that can be many of these buildings are important part of solved, emphasizing the building types that were architectural and cultural heritage and their repeatedly used. The idea is to propose some refurbishment demands specific and more guidelines for interventions on the envelopes of these complex approach buildings. 2.2 Post-war construction: 1946-1965 The building activity After the World War II, due to 2. CHRONOLOGY AND BUILDING TYPES the physical destruction (result of the war) and mass migration to the city (greatly result of political need to Table 1 presents the distribution of gross built create the “working class”) was quite intense and surface allocated for housing regarding the year of some 35% of present residential buildings were built in this period. Table 1: Overview of Belgrade's Building Stock

At first, the residential buildings were raised within their best, the buildings were complied to official the existing urban matrix, mainly substituting the standards that were rather up-to date at the time demolished ones. The next phase was formation of (revised U values and obligatory calculations of linear new blocks, so-called “pavilions” where several heat losses). buildings with mainly same design were forming the new urban entity: it started in existing urban tissue of 2.5 New Migrations: 1990's the city but soon it has stretched to New Belgrade2 Wars storming the former Yugoslavia and chaotic where extremely intense building activity took place. political situation were fatal for all urban and civic This period is very interesting because more or elements. Thousands of new immigrants fled to less same architecture, building design, technology, Belgrade, and the easiest way to "deal" with new materials, and spatial organisation was implemented. housing problems was to tolerate illegal construction. It would be further elaborated in this paper because it It is estimated that more than 100 0003 buildings were provides wide potential for future interventions. The constructed illegally, mainly in Belgrade and other main characteristics that distinguish this portion of urban areas. Built with no technical documentation Belgrade’s building stock are: and without building permissions, the vast majority of no thermal insulation - the first regulations this built corpus shows poor energy performance4. regarding building physics were introduced in Since all of these houses are to be submitted to 1967 technical and legislative evaluation, converting them long life span of primary construction – to higher standards concerning energy performance although built with rather limited resources, they could produce result equal to optimising the city of are made of solid, traditional materials (mainly population of 200 000 - 300 000. However, the first brickwork and concrete) phase of "legalisation" revealed a serious problem of limited architectural value – providing space (im)possibility to process such huge number of for interventions regarding appearance and applications. The ecological impact of this part of the identity building stock is significant, but still hard to estimate, repeated use of same model – this means that let alone regulate and will surely be subject of future the same guidelines could be applied on a large research. Being so, it is not further referred to in this number of buildings paper.

2.3 Directed housing strategy: 1966-1980 2.6 Entering the 21st century Overall progress during the late 60's and Higher energy prices that came with transition throughout the 70's reflected on architecture and processes resulted in somewhat changed approach building industry. Prefabrication was dominant, "new to the energy use in housing. Still far from general housing" was encouraged, the production was up to awareness for environmental issues, but with certain 14000 flats per year, technical and architectural economical motives, the attitude of investors and standards were significantly improved compared to users is changing. the previous two decades. Many options for If we treat the existing building stock as a modernisation and improving energy efficiency resource, it is important to identify segments that remain open, but several key issues make facade would be the most suitable to start with. Taking into interventions less likely to occur in recent future: the consideration the building types presented in this existence of thermal protection - multy-layered chapter, the two periods seem to have high capacity walls with thermal insulation and double-glazed for energy-efficient adaptation: windows make their energy performance post-war production - buildings constructed acceptable at the time after World War II, until late 1960's; architectural values and diversity - this period illegal housing – mostly constructed during is also characterised by numerous and fruitful 1990's, but still extremely difficult to handle research in apartment design and experiments in architectural form of prefabricated buildings. As the result of such tendencies, many housing 3. SAMPLE FACADES blocks contain certain architectural, sometimes even sculptural value and require specific In previous chapter, we have identified the approach regarding intervention in their buildings of co-called post-war production as the most appearance. suitable sample of Belgrade's building stock that could be revaluated and refurbished. 2.4 Early Market: 1980-1990 As the SFR Yugoslavia was getting weaker, so 3.1 Appearance and Orientation did the giant state-owned construction companies. Uniform approach to housing in this period The production was being reduced year after year; resulted in uniform appearance of buildings. Figures 1 data shown on Table 1 are based on the date of to 3 show "different" examples. completion and many houses numbered in this section are in fact representatives of previously described directed housing policy. Despite general stagnation, some form of rudimental real-estate market is emerging, and though neither quality of materials nor architectural value of the design were at

3.2 Structure The absence of diversity is also notable in materials and techniques used. The materials used for external walls, finishing and windows are almost completely the same on numerous buildings and blocks, built all over the city. Table 2 presents the most common elements of external walls

Table 2: Structure - the Most Common Elements walls masonry concrete 38cm 25cm finishing decorative Figure 1: Building as a part of a traditional city block mortar rendering windows double sash single sash

Presence more less

4. INTERVENTIONS

4.1 The Guidelines In order to improve the overall energy performance of certain building, the interventions on its external walls are usually concentrated on three aspects:

the use of materials, modifications in layers Figure 2: Stand-alone building within the city block openings - “perforation” adding new volumes, application of double

skin facades

4.2 New Layers Most buildings from the "post-war production" have external walls made of brick or of concrete (Table 2), in both cases with no cavities. Positioning of thermal insulation is therefore limited to either side of the facade. Although there are numerous technical solutions available, our goal was to identify the ones that are the most likely to occur. Internal insulation is generally less efficient but in certain circumstances it could be a first choice. The strongest reasons that lead to this solution are: Individual owners: The apartments are privatized, but the ownership of the building itself is unclear. That complicates the decision-making process since the tenants are never unanimous, Figure 3: New Belgrade - "The Pavilions" some not willing to participate, some not able to finance the modernisation etc... The fact that the Apparently, answer was the same regardless of internal insulation can be done individually makes it the situation. Refurbishment of these buildings opens quite convenient in such situations. The positive possibilities for revitalisation on all levels, new design results in individual units can also encourage the and new urban valorisation. others to make same modifications Almost all buildings erected during this period No heating installations: Most buildings from were designed with no concern to microclimate this period do not have central heating. Over last 4-5 parameters. Facades are the same, regardless to years the city authorities are promoting and their orientation, dominant winds, or conditions encouraging campaign of connecting "old" buildings related to a specific site. to central heating network. Since connecting implies

installation of radiators and horizontal branching are rather thick and this results in much better U within apartment units, at the same time insulation values compared to the internal insulation. Again, for can be added so that thermal and aesthetic qualities illustrating calculation, one of the cheapest examples are harmonized. was taken - compact insulation slabs with matching Simple and cheap: The most common render finishing. U values of 0.32 W/m2K for brick wall example of internal insulation is shown on Figures 4 (Figure 4) and 0.36 W/m2K for concrete wall (Figure and 5 - rather thin layer of thermal insulation (5cm) 5) are obviously superior to the internal insulation. with gypsum-plaster boards finishing and vapour Due to minimised cold bridging and linear losses, damp where necessary. These materials are the overall reduction of heat-loss for a complete affordable and easy to install, and such works could building would show even bigger difference. be carried out throughout the year, regardless the weather conditions.

Figure 4: Typical Brick Wall - the Most Probable Figure 5: Typical Concrete Wall - the Most Probable Interventions and Relevant U Values Interventions and Relevant U Values Applied on typical brick wall this type of internal insulation reduces the U value from 1.23 W/m2K Usually, the tenants are unwilling to undertake (original uninsulated wall) to 0.48 W/m2K (Figure 4). such interventions. Up to now, adding the external On concrete walls, the effect is stronger, reducing the insulation on those buildings was done only as U value from 2.31 W/m2K to 0.58 W/m2K (Figure 5). compensation: an investor would add some new External insulation is generally more favourable floors (vertical extension) and in return, he would since it uses the thermal capacity of the original wall. execute some construction works of common interest As shown in Table 2, the walls of sample buildings for all tenants. Vertical extension also provides new

roof for the building, so than the complete envelope be modernized to meet present housing standards, becomes properly insulated. but the basic layout has its limitations.

4.3 Openings Buildings from post-war period are very modest CONCLUSION in many aspects and openings and glazed surfaces are reduced to what was considered the "optimal" Only minor portion of Belgrade's building stock is size (recommended minimum glazing surface 1/7 of built in accordance to present regulations regarding room's floor area). Buildings shown on Figures 1-3 energy performance of buildings, and more than 50% have almost identical windows, and this principle was has no thermal insulation at all (Table 1). This means used with very rare exceptions. Therefore, that a complex and significant body of buildings can considering further reductions of glazed surfaces is be modified to meet the present standards and needs not the issue for such buildings. Some improvements related to contemporary living. in energy efficiency could be achieved when the Two periods of the last century can be identified windows are being changed - using proper frames, as the most interesting for energy optimisation: the sashes and glazing and with precise detailing post-war production and illegal housing. Due to the following installation of new window units or new lack of relevant data related to illegal housing, its insulation layers of external walls. potential is rather difficult to estimate at the moment. Table 2 shows that most windows from this On the other hand, the post-war production was period are double-sashed (always wood). When rather uniform and intensive. This resulted in a large changed, the most popular choice is single-sashed, number of very similar buildings, where same type of double-glazed window made of composite plastic technological solutions can be used repeatedly in materials. Its thermal performance is satisfactory, but numerous examples5. Optimization of this portion of environmental aspect of materials used is very Belgrade's building stock could be as productive as questionable. an optimization of a complete town. This paper has Simple solutions for either internal or external presented some simple interventions on building's insulations described in chapter 4.2 enable easy envelope with significant impact on energy detailing even when the original windows remain performance of a building and therefore the balance unchanged. The type of window fixing with somewhat on the city level. On a typical brick wall, with the most recessed position of window frame that was standard common intervention, the U value can be reduced at the time (external dimensions of opening from original 1.232 W/m2K down to 0.48 W/m2K with approximately 12cm smaller than internal dimensions) internal insulation and to 0.32 W/m2K with external enable better sealing. insulation. For concrete wall, these values would be 2.31 W/m2K (no insulation) 0.58 W/m2K (internal 4.4 New Volumes, Double Skins insulation) and 0.36 W/m2K (external insulation). Narrow loggias and balconies of post-war buildings (Figures 1-3) have certain potentials when used as a layout for buffer zone: outer glazing is easy to apply following their repeated pattern. 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