Lisø PhD Dissertation Manuscript - NTNU

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flashing techniques were involved in approximately 25% of all the masonry defect cases (Kvande & Lisø, submitted). Furthermore, the last mentioned investigation concludes that shrinkage and thermal expansion/contraction without the necessary countermeasures are the most common cause of masonry defect, registered in one third of all cases of defects analysed (302 process induced building defect assignments related to masonry in the 20-year period 1983-2002). This investigation also reveals that two thirds of all cases comprise faults in the execution of the actual rain barrier (non water-tight mortar joints and rendering), drainage from the air gap (insufficient air gaps, mortar bridges between outer leave and rear wall as well as missing drainage openings at bottom of wall) and the execution of window and parapet flashing. 4 DISCUSSION AND LIMITATIONS The analysis is based on building defect assignments carried out by SINTEF Building and Infrastructure and thus cannot aspire to represent a complete and definitive overview of process induced building defects in Norway. In geographic terms, building defect assignments forming part of the investigated 10year period have been carried out in 182 municipalities out of a total of 436 municipalities in Norway. However, a major part of the cases of defects are located in municipalities near SINTEF Building and Infrastructure’s offices in Oslo and Trondheim. This is due to the institute having easier access to building defect assignments in its vicinity. The municipalities of Oslo and Trondheim alone reply for 38% and 11% of the investigated cases respectively. There is naturally a wide range of causes as to why the different actors within the industry contacts SINTEF for an expert opinion, assessment or investigation of a building defect incident. In most cases the client is concerned with the extent of the defects, and loss of reliability or reductions in lifetime of the component exposed to damage. The clients also often want advice as to how the defect or damage should be repaired. In some cases the institute is addressed to settle a dispute between different actors involved in the construction process. The institute is also used as independent experts in cases to be solved by the judicial system. It is therefore important to emphasise that only a small part of the total amount of process induced building defects in Norway emerges in the SINTEF Building and Infrastructure’s building defects archive. The following conditions or circumstances will contribute to a restriction in the selection of building defect assignments: − The probability that a certain defect will emerge in the archive will be higher the more difficult it is to find a good solution to the problem, or the more ambiguously conditions regarding responsibility are described. − It is reasonable to assume that the costs involved in the assignment of the institute as expert advisors make professional actors dominant. This probably also explains the large amount of complex and expensive defect cases in the archive. Changes in the institute’s time rates compared to the general economic trend in the society, and changes in the institute’s price policy, could also entail changes in the amount and type of defects to be registered in the archive. − It is reasonable to assume that the inflow of assignment reports is strongly related to areas of expertise where SINTEF Building and Infrastructure has a good reputation. Thus, changes in the institute’s competence profile could entail changes in the amount and type of building defect assignments. One of the major advantages with the archive is clearly the large amount of assignments over a long time period. Also, the archive contains thorough descriptions of cause, extent and preventive actions on complex building defect cases, investigated and described by highly competent researchers. Despite the presented investigation having quantitative shortcomings in terms of general validity, it is an important step towards a qualitative identification of problem areas. The ongoing establishment of the described building defects archive will be an important tool in both the continuous efforts towards higher quality in the construction industry and the development of strategies aiming at learning from experience. It will also be a significant instrument in the development of appropriate preventive actions. The archive will finally be an important element in the continuous development of more accurate criteria and Codes of Practice regarding the design and functionality of critical elements of buildings in the SINTEF Building Research Design Series. 5 FURTHER WORK Empirical observations and modelling increasingly point to global warming and long-term changes in the climate system. The Intergovernmental Panel on Climate Change concludes that most of the warming observed over the last 50 years is attributable to human activities, and that anthropogenic climate change is likely to persist for many centuries. The presented review of building defects will be further developed and used to prepare a review of the robustness of the Norwegian building stock and building practice. SINTEF Building and Infrastructure, as an independent institution developing technical guidelines that reaches out to almost all actors in the
construction industry, and academic institutions like NTNU have an important role to play in the development of strategies aiming at building awareness of the future risks of climate change and in the development of precautionary and cost beneficial adaptation measures (Lisø 2005). At present, building design codes, standards and operational procedures are based on historic weather data. The existing building stock is in the next decades likely to be exposed to significantly different climatic strains than they are today, due to climate change. The robustness of the Norwegian building stock will be assessed through analysis of statistical data, along with SINTEF Building and Infrastructure’s experience with building defects. Statistical data for e.g. building types, year of construction and geographical localisation of the approximately 3.68 million registered buildings in Norway are available in the Ground Property, Address and Building Register (GAB). Approximately 1.4 million buildings are for residential purposes. The municipalities record data in GAB (all buildings in Norway larger than 15 m 2 are to be recorded in the register with a code for building type and coordinates). Historic trends in the design and construction of buildings and built environments will also be studied. Historic weather data and statistical data from insurance companies (natural damage) will serve as an enlarged basis for the analysis. The design of building envelopes should be expected to be the result of choices based on optimally utilised information and knowledge on both building technology and the different impacts the buildings are exposed to (Nordvik & Lisø 2004). Several sources of uncertainties exist related to both scenarios for global climate change, and to the effects of global warming on regional- and local-level climate in different parts of the country. However, an increased focus on the impacts of different climatic parameters on building envelope performance will lead to a more climate adapted design in new construction, and also a more robust performance of existing buildings. The work presented here allows for in-depth analyses of causal relations of different types of building defects on a wide variety of building envelope elements. Final results from these ongoing investigations, together with comparisons with prospective corresponding international research within this area, will be published in due course. 6 CONCLUDING REMARKS Defects related to the building envelope constitute 66% of the investigated process induced building defect cases in the 10-year period 1993-2002. Moisture as the main source causing the defect replies for as much as 76% of all investigated cases in the 10-year period. Many types of building defect cases are recurring items, which indicate a general lack of knowledge amongst the different actors in the construction industry concerning fundamental principles of building physics in particular. It is possible to reduce the amount of building defects in Norway. This would require a determined and active effort in several areas and by several actors within the construction industry. To reach future national defined goals on building defect reduction it is crucial to be familiar with both the technical and process induced causes initiating defects or damage. A future national building defects archive, in which the here-described archive should be a central contribution, would be an important part of this work; as such an archive would shed light on the underlying causes of defects and enable assessment of preventive actions. The presented process induced building defects archive will also be an important educational tool in the establishment of knowledge and experience on building defects amongst academic institutions and different actors in the construction industry. ACKNOWLEDGEMENTS This paper has been written within the ongoing SINTEF research & development programme “Climate 2000” (2000–2006), strategic institute project “Impact of climate change on the built environment”. The authors gratefully acknowledge all construction industry partners and the Research Council of Norway. A special thanks to Thorbjørn Ingvaldsen for valuable comments, and Vidar Sagen and Pål Bjerkevoll (master students at NTNU) for their registration work. The authors are also indebted to the invaluable assistance from Karin Leira and Christer Isberg Eng at SINTEF Building and Infrastructure’s Central Archive. REFERENCES Bjerkevoll, P. 2004. Ytterveggskonstruksjoner - Byggskadeanalyse (External wall structures - Building defect analysis, in Norwegian). Project Thesis, Department of Civil and Transport Engineering, Norwegian University of Science and Technology (NTNU), Trondheim. Bjerkevoll, P. 2005. Klimapåkjenninger og prosessforårsakede byggskader (Climatic impact and process induced building defects, in Norwegian). Master Thesis, Department of Civil and Transport Engineering, Norwegian University of Science and Technology (NTNU), Trondheim. Bornehag, C.G, Blomquist, G., Gyntelberg, F., Jarvholm, B., Malmberg, P, Nordvall, L., Nielsen, A., Pershagen, G. & Sundell, J. 2001. Dampness in buildings and health. Nordic interdisciplinary review of the scientific evidence on associations between exposure to “dampness” in buildings and health effects (NORDDAMP). Indoor Air 11:72-86.
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degree of saturation, freezing will
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accelerated frost damage or frost d
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A possible objection to the present
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[17] Dührkop H., Saretok V., Sneck
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Decay potential in wood structures
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Wood decaying fungi will only be ac
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to promote decay prevails. Two of t
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Acknowledgements This paper has bee
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(a driving rain gauge), however, is
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Fig. 1. Map of Norwayshowing the lo
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Frequency 25 20 15 10 5 0 highest p
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interesting to compare those result
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Effects of wind exposure on roof sn
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In ISO 4355 ”Bases for design of
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variety of roofs and wind exposures
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Li and Pomeroy [13] evaluated hourl
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Fig. 5. Exposure coefficients for 3
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meteorological stations are expecte
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Many of the meteorological stations
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the ground with return period of 30
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References [1] Standards Norway. De
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