Low Energy Renovation of Buildings Using Prefabricated Systems

Transcription

1 Low Energy Renovation of Buildings Using Prefabricated Systems Helena Corvacho 1 Joana Sousa 2 Luís Pedro Pereira 3 Marisa Quintela 4 ABSTRACT In the scope of IEA ECBCS Annex 50 Prefabricated Systems for Low Energy Renovation of Residential Buildings, the development of an integrated modular concept for the renovation of building envelopes was performed. The design of innovative facade retrofit modules was carried out. In order to evaluate the application potential of these facade modules, national building stock was characterized and repair needs were identified. A detailed analysis of a sample of 132 buildings was then performed to define the current morphology of the facades to be renovated. For the particular case of social housing which is now the object of a large retrofit campaign, different scenarios of retrofit design were considered and studied, identifying the main difficulties and discussing the possible solutions. The design of the facade retrofit solution for seven social housing neighbourhoods using facade modules was performed and evaluated. In this paper, some of the results of these tasks are reported and discussed. It was concluded that there is an opportunity for the application of the integrated modular concept for a low-energy renovation of buildings in Portugal but it is very important to optimize the solutions in economical, technical and environmental terms for the guarantee of their sustainability. KEYWORDS Low energy renovation, Prefabricated systems, Sustainability. 1 University of Porto, Faculty of Engineering, Building Physics Laboratory (FEUP), Porto, PORTUGAL, corvacho@fe.up.pt 2 University of Porto, Faculty of Engineering (FEUP), Porto, PORTUGAL, ec09311@fe.up.pt 3 University of Porto, Faculty of Engineering (FEUP), Porto, PORTUGAL, ec05121@fe.up.pt 4 University of Porto, Faculty of Engineering, Building Physics Laboratory (FEUP), Porto, PORTUGAL, marisa@fe.up.pt

2 Helena Corvacho, Joana Sousa, Luís Pedro Pereira and Marisa Quintela 1 INTRODUCTION The aim of the international project IEA ECBCS Annex 50 Prefabricated Systems for Low Energy Renovation of Residential Buildings was to develop a new concept of integrated low energy retrofit of a whole building using prefabricated solutions. The development of prefabricated modules for the retrofit of facades was performed within the scope of the definition of advanced retrofit strategies. A building strategy determines which investment should be made for a certain period of the building s service life. Today, a long-term building strategy is often lacking. Retrofit measures are often only tackled when they are unavoidable. This leads to uncoordinated, partial renovations that eventually result in additional costs. An advanced retrofit strategy aims at establishing a holistic building approach for the entire remaining life cycle of the building. The ultimate option in the building strategy is to construct a new building in replacement. An advanced retrofit strategy determines whether a building reaches this condition in five, twenty-five, or one hundred or more years. Intermediate objectives of an advanced retrofit strategy can be building maintenance, partial renovation or comprehensive renovation [Schwehr, P. et als 2010]. The definition of these retrofit strategies must rely upon some important actions, namely, the market potential evaluation (considering the main parties: owners, tenants, contractors, construction products manufacturers and providers, public authorities), the retrofit needs evaluation, the analysis of the buildings and the target agreement (through an added value checklist). For the Portuguese situation, retrofit needs were evaluated and an analysis of the morphology of buildings was performed in order to estimate the potential of application of prefab solutions. The focus was on facades retrofit. This study was carried out having in mind the type of retrofit prefabricated modules developed within the scope of IEA ECBCS Annex 50 (figure 1). Swiss module Austrian module Portuguese module Figure 1. Some prefab modules developed by IEA ECBCS Annex 50 [Geier, S. et als 2010]. A thorough study of the Portuguese housing stock was carried out. In the most recent statistics, there were 3,160,043 buildings in Portugal mainland and islands. However not all buildings were considered. The present study was focused on residential buildings so every non-residential building was disregarded. Furthermore, for reasons that will be explained below, a target group was defined: residential buildings built between 1919 and 1990, with 2 to 6 floors and presenting some repair needs in their exterior walls and windows. In this context, around buildings were estimated as having potentially favourable conditions for retrofit using prefabricated facade panels. However determining the number of potential targets for 2 XII DBMC, Porto, PORTUGAL, 2011

3 Low Energy Renovation of Buildings Using Prefabricated Systems buildings retrofit is not enough by itself to get an idea of the applicability of this technique. Other issues must be addressed, like architectural, technical, environmental and economical evaluations. In architectural terms, the choice of a particular panel depends first on the morphology of the facades and the shape of their openings. Since there is no statistical information regarding these elements in Portugal, a study was carried out in-situ by observing and coding openings of 132 buildings chosen randomly in a geographical area as broad as possible, but with significant urban characteristics. In parallel, it was evaluated what could be the possible application of the prefabricated modules proposed by the international project ECBCS IEA Annex 50 in the specific case of social housing. This housing stock was chosen due to its homogenous and repetitive typologies. Some neighbourhoods were selected so as to obtain a significant sample with a large number of buildings with clearly defined characteristics and types. This study lead to an exercise on geometrical features through the study of architectural elevations of facades, taking into account the various singularities that compose them (like recessions, projections, number and size of openings, size of spans, etc.). In this work, a reflection was made on the choice of materials which is fundamental for the durability of the solution. Beyond mechanical resistance, there are still a number of other requirements that panels should ensure which are associated with a long service life. They must comply with requirements of safety (structural, fire risk), tightness (water, air), comfort (acoustic, thermal, luminous) and, at the same time, present cleaning and maintenance needs that are easy to undertake and within a reasonable cost. The expected durability of the solution with routine maintenance actions must be enough to justify the investment in the retrofit. 2 APPLICATION POTENTIAL OF PREFABRICATED MODULES FOR THE RETROFIT OF FACADES IN PORTUGAL 2.1 The Portuguese Housing Stock State of the existing buildings Within the housing stock, three major groups of buildings were described: those with no repair needs, those needing some repair actions and those that are highly degraded. Figure 2 shows the percentage distribution that characterizes the state of the existing buildings in what concerns external walls and windows. 4% 43% 53% No repair needs Needing repair actions Highly degraded Figure 2. State of the existing buildings external walls and windows. XII DBMC, Porto, PORTUGAL,

4 Helena Corvacho, Joana Sousa, Luís Pedro Pereira and Marisa Quintela Number of Floors As seen in Figure 3, about 44% of the residential buildings have two floors and 42% just one floor. The sum of the remaining buildings which have more than two floors represents 14% of the total number of residential buildings. 2,5% 9,0% 44,0% 1,0% 0,6% 0,9% 42,0% 1 floor 2 floors 3 floors 4 floors 5 floors 6 floors 7 or more floors Figure 3. Percentage distribution of buildings per number of floors Date of Construction The date of construction is also an important parameter to be considered. In the twentieth century, the time in which there was a higher production of buildings in Portugal was the period from 1981 to 1990, as it can be seen in Figure 4. Number of buildings Before to to to to to to 2000 Figure 4. Number of new buildings per period of construction. 2.2 Definition of a Target Group of Buildings A target group of buildings was defined based on the study of the housing stock. First, it was considered that only the buildings with some need of repair actions in external walls and/or windows would be possible objects for the application of the prefab modules. The need for repair is certainly not a necessary condition for the renovation of a building but it is undoubtedly a major argument for it. It is quite probable that, in those circumstances, a major renovation is better understood and accepted by the inhabitants. 4 XII DBMC, Porto, PORTUGAL, 2011

5 Low Energy Renovation of Buildings Using Prefabricated Systems It was decided to exclude buildings that have only one floor as well as buildings with seven or more floors. The exclusion of buildings with only one floor is related to the great architectural variability of the facades of those buildings, making it difficult to apply standardized solutions even if flexible and versatile. Furthermore, an integrated prefabricated system would be too expensive for small buildings because it would be impossible to implement a certain kind of large scale saving. It must be pointed out that this exclusion represents about 42% of the households in the country which is quite significant. Buildings with seven or more floors were also excluded due to the difficulty of lifting large-scaled components, requiring exceptional and expensive means. In what concerns the age of the buildings, the aim was to exclude the too old and the too recent buildings. Those that were built after 1990 had already to comply with the thermal regulation in force since then and although in many cases there is still some margin to improve their energy efficiency, those buildings were considered out of the main target group. All buildings built before 1919 were also not included in this study. The period of time considered was then from 1919 to However, in the group of buildings built between 1919 and 1960, there is certainly a high probability that a major low-energy renovation is not technically possible or economically justifiable. So, within the target group, a sub-group was identified, the one for buildings constructed from 1961 to 1990 which will constitute the main field of application of the retrofit strategies under analysis. 2.3 Characterization of the Morphology of Facades and Evaluation of Prefab Modules Applicability Analysis of a random sample of 132 buildings The determination of the potential applicability of prefabricated facade modules in buildings of the target group was performed by the observation in-situ of a considerable number of facades in order to identify their usual morphologies. Focusing on the number and type of openings in the facades of the buildings a coded classification was developed based on the following parameters: type of opening (cod.1- window; cod.2 - window behind balcony; cod.3 - door behind balcony), vertical alignment of openings (cod.1 - aligned openings, cod.2 - openings non aligned) and horizontal position of openings (cod.1- openings in a short distance from each other; cod.2 - openings in an intermediate position; cod.3 openings in a large distance from each other; cod.4 - openings near to an adjoining building; cod.5 projected openings; cod.6 - openings along the side of a projection of the building; cod.7 openings in a recessed wall of the building; cod. 8 - openings in a projected wall of the building; cod. 9 enclosed balconies, cod.10 - openings along the side of a balcony; cod.11 openings between balconies). A detailed presentation of this analysis was included in [Sousa, J. 2010]. In Table 1 the part of the openings classification that concerns their horizontal position is shown. As said before, a sample of 132 buildings was analyzed. In a first step, 1282 openings in 93 buildings were characterized. In a second step, 508 openings in 39 buildings were added. With this two step analysis it was possible to find a similar percentage distribution of the different types of openings. The characterization of the facades morphology allowed an estimation of the potential use of different types of prefabricated modules. XII DBMC, Porto, PORTUGAL,

6 Helena Corvacho, Joana Sousa, Luís Pedro Pereira and Marisa Quintela Table 1. Characterization of facades morphology horizontal position of openings [Sousa, J. 2010]. Cod. 1 Openings in a short distance from each other Cod. 2 Openings in an intermediate position Cod. 3 Openings in a large distance from each other Cod. 4 Openings near to an adjoining building Cod. 5 Projected openings Cod. 6 Openings along the side of a projection of the building Cod.7 Openings in a recessed wall Cod. 8 Openings in a projected wall Cod.9 Enclosed balconies Cod.10 Openings along the side of a balcony Cod.11 Openings between balconies The case of social housing Sample characterization A sample of seven social housing neighbourhoods, in Porto and Vila Nova de Gaia, in sum 107 buildings with a total of 2808 dwellings were chosen so that it had some statistical significance. As explained before, these buildings were chosen because of their homogeneous and repetitive typologies (as it can be observed in Figure 5), however, in each selected neighbourhood, all the buildings with different characteristics were picked up to better identify all potential problems in applying prefabricated solutions for the retrofit of facades. This analysis was carried out in the scope of the work presented in [Pereira, L. P. 2010]. For each of the seven neighbourhoods beyond the generic features like designation, location, date of construction, number of buildings, number of entrances, number of floors, number of dwellings, etc., more specific characteristics were carefully analyzed, some of them essential for the choice of the prefab panels to be used: type of structure, location of the structural elements (essential for the determination of the fixations of the retrofit system), floor to floor height, number and size of spans, number and types of openings ( see classification above), type of usage, drainage system pipes along the facades (evaluation of their integration in the retrofit modules), etc Evaluation of the applicability of panels The "puzzle" of the panels was designed for the facades of the different buildings under analysis (examples in Figure 5). The position of the structural elements (slabs, beams and columns), since these are the points where panels must be fixed, served as reference lines. The location of downpipes was also taken into account in order to integrate them in special voids created within the prefabricated modules. Ventilation pipes or other installations were also to be integrated. 6 XII DBMC, Porto, PORTUGAL, 2011

7 Low Energy Renovation of Buildings Using Prefabricated Systems The dimensions of the modules were defined in such a way that they were not too low that they compromised the advantages of the system nor too high that they demanded high costs of transport and placement. The maximum dimensions of the panels were 3.0 x 3.0 metres. Figura 5. Examples of application of facade modules. 3 DISCUSSIONS In architectural terms this study proved that there is a considerable potential for the application of retrofit prefabricated façade modules among a target group of buildings that includes the more standardized buildings of social housing estates. In technical terms, the prefabrication is an old but renewed challenge. The panels that have been developed within the scope of Annex 50 express a new integrated retrofit concept resulting from an holistic approach to the buildings. Furthermore three fundamental guidelines were taken: the modules are standardized in construction, layers and joints; the modules are flexible in architecture, form and cladding; the modules can be combined with each other and with non-prefabricated (conventional) retrofit options [Schwehret als 2010]. In [Abreu et als 2010] the new technological challenges in the low-energy retrofit of external walls of buildings were discussed having in mind the economical and technical environment of the country. As it was mentioned, a significant part of the Portuguese housing stock presents repair needs. This should be looked at as an opportunity to re-qualify the buildings, making them more energy-efficient and more comfortable. The prefabrication, which has always been considered unsuitable for the small Portuguese market of buildings and also not compatible with the small size of the great majority of the companies in the construction sector, should be able to present solutions that provide innovative functions (integrating pipes, ventilation, etc.), that are flexible enough to allow for a great diversity of facades and a great variation in mounting conditions (different companies, different sites), that are not closed systems, i. e., that can be combined with other options and that represents a strong contribution for a low-energy running of the building (through integrated passive systems, for instance). All this must be reached at a reasonable and competitive cost. In economical terms, one can argue that in a small country large-scale savings are not easy to achieve. However, there is also an important argument in favour of the prefabrication solutions that is the fact XII DBMC, Porto, PORTUGAL,

8 Helena Corvacho, Joana Sousa, Luís Pedro Pereira and Marisa Quintela that a long service life is more easily ensured due to the more demanding quality control in production and also because it is easier to plan a rational maintenance along its service life. 4 CONCLUSION Portugal presents a significant part of its housing stock in need of repair actions. This should be considered as an opportunity for a low-energy renovation of the buildings. In the scope of the work of International Energy Agency ECBCS Annex 50, prefabricated modules for the retrofit of facades have been developed (and will be tested and monitored). The potential for their application in Portugal was evaluated and it was concluded that around buildings have favourable conditions for retrofit using prefabricated facade panels. For this to be effective, careful technical, environmental and economical evaluations are needed. ACKNOWLEDGMENTS The participation of the first author in the work of the International Energy Agency ECBCS Annex 50 - Prefabricated Systems for Low Energy Renovation of Residential Buildings was undertaken in the scope of the project PTDC/ECM/67373/2006 Reabilitação Energética de Edifícios (Low Energy Retrofit of Buildings) funded by Portuguese Foundation for Science and Technology (FCT), from February 2008 to end of January REFERENCES Abreu, I. & Corvacho, H., 2010, Os Novos Desafios Tecnológicos na Reabilitação Energética de Paredes Exteriores de Edifícios (The New Technological Challenges in the Low Energy Retrofit of External Walls of Buildings), in Construção Magazine, nº 35, Publindústria, pp Geier, S., Höfler, K., Cousin, S., Silva, P., Kobler, R., 2010 (draft) Retrofit Module Design Guide, IEA ECBCS Annex 50, Prefabricated Systems for the Low Energy Renovation of Residential Buildings, 133 pp., Swiss Federal Laboratories for Materials Testing and Research, Switzerland. Pereira, L. P. 2010, Reabilitação Térmica de Fachadas. O Exemplo dos Bairros Sociais (Low Energy Retrofit of Facades. The Example of Social Houses), Ms. Sc. Thesis, 81 pp, Faculty of Engineering of the University of Porto, Portugal. Schwehr, P., Fischer, R., Geier, S. & Höfler, K (draft) Retrofit Strategies Design Guide. Advanced Retrofit Strategies & 10 Steps to a Prefab Module, IEA ECBCS Annex 50, Prefabricated Systems for the Low Energy Renovation of Residential Buildings, 112 pp., Swiss Federal Laboratories for Materials Testing and Research, Switzerland. Sousa, J. 2010, Potencial da Aplicação de Sistemas Pré-fabricados na Reabilitação Térmica de Fachadas (Application Potential of Prefabricated Systems for the Retrofit of Facades), Ms. Sc. Thesis, 118 pp, Faculty of Engineering of the University of Porto, Portugal. 8 XII DBMC, Porto, PORTUGAL, 2011