Lisø PhD Dissertation Manuscript - NTNU

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LisÖ et al. related to broken roofing tiles, especially in connection with valley gutters. Short overlapping at jointing has resulted in cases of leakage. The same applies when the under flashing is missing. Another typical problem is the tendency to use too narrow widths on both valley gutters and abutment gutters. Experience has shown that a width of 50 mm on abutment gutters is too narrow. Recommendations for further work The work presented here is embedded within the ongoing NBI Research & Development Programme ‘Climate 2000’ (Lisø et al., 2004). The present authors’ ambition is to use the results from the present investigation as a tool for further studies on the performance of weather-protective flashing in severe climates. Building damage records in NBI’s archives reveal serious deficiencies in the construction industry when it comes to knowledge concerning the planning, design and construction of weatherprotective flashing. The investigation presented here has revealed a number of typical problem areas. The results will be used as a basis for planning new field studies and laboratory investigations. The field study will be undertaken as the basis for a systematic review and assessment of various forms of flashing design. The study will be carried out in close cooperation with the construction industry. The laboratory investigations will be carried out to analyse how various types of weatherboard flashing can provide a shield against precipitation. The test arrangement will encompass techniques that are expected to be good, average and possibly deficient/ unsatisfactory. The tests will be carried out in a turnable equipment for full-scale rain and wind tightness testing (RAWI box). The main objective will be to obtain a basis for the ranking of different flashing designs according to their performance in different climate situations. Conclusions and implications The transition from a prescriptive to a performancebased building code in Norway has strengthened the demand for supporting standards and easily accessible design guidelines and best-practice solutions. The widely recognized NBI Building Research Design Sheets comply with the requirements in the building code, and their main purpose is to provide solutions and recommendations that encourage high quality in the planning, design and construction of buildings in a country with an extremely variable climate. The presented investigation of NBI’s project archives reveals serious deficiencies in the construction industry 52 with regard to knowledge about the correct design and construction of weather-protective flashing, illustrating the need to obtain further knowledge on commonly used flashing solutions. The presented analysis clearly shows that certain faults and deficiencies are recurring items. Windowsill/weatherboard flashings comprise as much as 41% of the examined building damage cases associated with weather-protective flashing. Damage in connection with parapet flashing comprises 27% of all cases included in this investigation. With few exceptions, instances of damage are on Norway’s coastal areas. The presented analysis calls for a redefinition and strengthening of existing performance requirements for weather-protective flashings in severe climates as a basis for the improvement of existing flashing design, guidelines and workmanship. Flashing should always be designed and performed so that water is directed away from the structure, and rain or snow is not led underneath the flashing with the consequent risk of leaks. Generally, a flashing should not be the only tightening layer against water ingress. Flashing should function primarily as a drainage covering or external rain screen in a two-stage tightening (Figure 13). It will also act as a mechanical safeguard for any underlying barrier layer, e.g. roofing. The flashing and underlying structure must always be designed so that any possible water entering behind the flashing will not penetrate the structure behind. Simplified flashing solutions could be acceptable in areas with low and moderate driving rain exposure. However, the economic benefit from such simplification is marginal. In light of a more severe climate in parts of the country due to global warming, or rather the uncertain risks of future climate change, it would be a fairly inexpensive insurance to choose flashing solutions with a higher climatic safety level. The results from the investigation, revised and improved high-performance flashing solutions for typical problem areas, will be incorporated in the appropriate Building Research Design Sheets. Figure 13 Principle of one-stage tightening (left) and two-stage tightening (right)
Acknowledgements This paper was written within the ongoing NBI Research & Development Programme ‘Climate 2000–Building Constructions in a More Severe Climate’ (2000–06), the strategic institute project ‘Impact of Climate Change on the Built Environment’. The authors gratefully acknowledge all their construction industry partners and the Research Council of Norway. A special thanks to Søren Tybring Haug and Trond Opheim, Norwegian Association of Ventilation, and Tinsmith Companies for valuable comments on revised flashing solutions, and to David H. Lovett for assisting in editing an early draft of the paper. References Baker, M.C. (1965) Flashings for Membrane Roofing. Canadian Building Digest, CBD-69, National Research Council Canada, Institute for Research in Construction, Ottawa. Evensen, M. (2003) Beslag [Flashings]. Master’s thesis, Norwegian University of Science and Technology (NTNU), Trondheim. (in Norwegian) Geving, S. and Thue, J.V. (2002) Fukt i bygninger [Moisture in Buildings]. Handbook No. 50, Norwegian Building Research Institute, Oslo. (in Norwegian) Harila, R. (2002) Beslag mot nedbør [Weather protective flashings]. Master’s thesis, Norwegian University of Science and Technology (NTNU), Trondheim. (in Norwegian) Ingvaldsen, T. (1994) Byggskadeomfanget i Norge [Building Damage in Norway]. NBI Project Report No. 163, Norwegian Building Research Institute, Oslo. (in Norwegian) Ingvaldsen, T. (2001) Skader pa˚ bygg: grunnlag for systematisk ma˚ling [Building Damage: A Basis for Systematic Evaluation]. NBI Project Report No. 308, Norwegian Building Research Institute, Oslo. (in Norwegian) Kvande, T. and Lisø, K.R. (2002) Beslag mot nedbør [Weather Protective Flashings]. NBI Anvisning 38, Norwegian Building Research Institute, Oslo. (in Norwegian) Kvande, T., Lisø, K.R. and Waldum, A.M. (2003) Rehabilitering av tak og teglfasader. HM Kongens Garde Huseby Leir [Rehabilitation of Roofs and Masonry Façades. His Majesty the King’s Guard Huseby Barracks]. NBI Report No. 116, Norwegian Building Research Institute, Oslo. (in Norwegian) Lisø, K.R., Aandahl, G., Eriksen, S. and Alfsen, K.H. (2003c) Preparing for climate change impacts in Norway’s built environment. Building Research & Information, 31(3–4), 200–209. Lisø, K.R., Kvande, T. and Myhre, L. (2003a) Klimaendringer, byggskader og norsk byggeskikk [Climate change, building damage and Norwegian building practice]. Plan (Universitetsforlaget, Oslo), no. 5. (in Norwegian) Lisø, K.R. and Kvande, T. (2004) Climate 2000 – Building Constructions in a More Severe Climate – Programme 2000– 2006. Programme Description, NBI Report No. O10210- 99, Norwegian Building Research Institute, Oslo. Lisø, K.R., Time, B., Kvande, T. and Førland, E.J. (2003b) Building enclosure performance in a more severe climate, in Carmeliet, J., Hens, H. and Vermeir, G. (Eds): Research in Building Physics – Proceedings of the 2nd International Conference on Building Physics, A. A. Balkema, Lisse, pp. 309–317. McDonald, J.R., Sarkar, P.P. and Gupta, H. (1997) Wind-induced loads on metal edge flashings. Journal of Wind Engineering and Industrial Aerondynamics, 72(1–3), 367–377. NBI (1991) Skader pa˚ takbeslag. A ˚ rsaker og utbedring [Damage on Roof Flashing. Causes and Repair Methods). Building Research Design Sheet 725.722. Building Research Series, Norwegian Building Research Institute, Oslo. (in Norwegian) High-performance weather-protective £ashings NBI (2000) Ba˚nd- og skivetekking med falsede tynnplater [Welted Metal Roofing]. Building Research Design Sheet 544.221. Building Research Series. Norwegian Building Research Institute, Oslo. (in Norwegian) Norwegian Standard 3420 (1999) Specification texts for building, construction, installations. Norwegian Standard, Standards Norway, Oslo. (in Norwegian) Pla˚tslageriernas Riksförbund (2002) Byggnadspla˚t 1–14, Pla˚tslageriernas Riksförbund, Stockholm. Appendix: De¢nitions The original Norwegian definitions used in this paper comply with the terms and definitions given in Norwegian Standard 3420 (1999). The following corresponding English equivalents have been used throughout. Abutment gutter A roof gutter that follows the slope of a roof (e.g. a gutter forleadingwaterintoorawayfromasurfacewhere the roof surface abuts the roof edifice or chimney) (see above), as well as a gutter compensating for the height difference in roof surfaces or coverings, or between differing coverings. A gable gutter is a typical abutment gutter. Bevel £ashing A flanged sheet metal covering (see the examples above) that protects the bevel (1) on a roof, e.g. a hipped roof. Fastening £ashing A flanged sheet-metal covering used to fasten the main flashing in order to achieve a concealed fastening and to avoid perforating the main flashing. 53
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Building envelope performance asses
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BUILDING RESEARCH &INFORMATION (200
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LisÖ et al. on how to cope with an
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LisÖ et al. the exposure to contin
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LisÖ et al. business premises. The
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LisÖ et al. construction industry
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Research in Building Physics, Carme
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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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