Lisø PhD Dissertation Manuscript - NTNU

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LisÖ et al. Figure 4 Recommended design of a window installation in the outer side of a cavity wall Figure 5 Recommended jointing of windowsill £ashing. Jointing must be located between the windows transition flashings also apply to balcony and top flashings, as well as flashings around ventilation louvres. Balcony and/or balustrade flashings are often penetrated when antennas, sunroofs, windshields, etc. are installed. Such devices should be fastened to the in- or outside of the parapet/balustrade without perforating the flashing or, alternatively, furnished with grommets and/or collars. The most common fault with regard to parapet flashing is the design of the jointing. Overlap jointing, often combined with nailing of the flashing at the top edge, can easily lead to leakage (Figure 6a). Few problems have been registered whenever welts have been employed (Figure 6b). Folded joints (welts) 48 Figure 6a The top of the parapet is formed as a ‘gully’. Overlap joints and nailing of the £ashing from above render the structure prone to leakage. Sealing solely with mastic is not effective in the long term. Source: Norwegian Building Research Institute,Oslo Figure 6b Jointing of parapet £ashing with double-raised welts (i.e. a double standing seam), and with possible sealant in the welt, provides a watertight joint incorporating a sealant are water resistant and permit thermal expansion/contraction. Parapets and gables with elevated projections of varying widths can provide challenging tinsmith work. With parapet projections, it is vital that flashings and roofing are formed in such a way that the sealing is not damaged. To diminish the visual impact of the parapet flashing, it is common practice to reduce the turndown along the facade. Too short turndowns make it possible for wind to blow water in under the flashing. The parapet flashing for multi-storey buildings should be drawn down a minimum 150 mm along the facade (Figure 7). Parapet flashings should act as outer rain barrier in a two-stage tightening, i.e. there must always be a tightening layer behind the parapet flashing. When the tightening layer under the flashing is missing, water ingress can easily arise. Also, in cases where the roofing material has not been drawn across the parapet under the flashing, water can enter under
Figure 7 Example showing the recommended construction of welted parapet £ashing the flashing (on the facade side) resulting in leakage behind the wind barrier. A recommended solution is shown in Figure 7. Fastening at the inward edge of the parapet must be positioned a minimum 150 mm above the roofing material in order to prevent leakage due to static water on the roof. This in turn necessitates a parapet that is not too low. When the turndown along the facade is finished off against the wall waist, rain striking the parapet is led directly in towards the facade. Depending on the facade material, this moistening can lead to staining and frost damage (Figure 8). Norwegian Standard 3420 stipulates finishing off a minimum 20 mm away from the wall waist. Among other factors, the necessary distance from wall waist depends on the height, form and location of the building. The parapet should always have a minimum 1:5 slope inwards towards the roof surface. An inwards incline reduces the danger of ice and/or snow sliding off the parapet. In addition, the slope is an important safeguard against static water, snow and/or ice and thereby water pressure on joints in the parapet flashing. High-performance weather-protective £ashings Figure 8 Finishing-off of the parapet £ashing against the wall face has led to wetting/moistening of the facade with consequent organic growth. Source: Norwegian Building Research Institute,Oslo Wall £ashing details The junction between the roof and adjacent, upper outer wall is a vulnerable point. For wood frame walls, the transition must be designed by finishing the roofing underneath the wind-barrier layer within the wall (Figure 9a). Leaks can easily arise whenever the wind-barrier/roofing material overlap is missing, even when the flashing is installed as a rain shield. The most frequent cases of registered damage are for masonry and concrete walls. A typical fault is flashing not being inserted in the mortar joint (notch), or where the insertion joint has become so jagged and uneven that water can run in behind the flashing. In the case of cavity walls, one must always expect water penetration through the external face of the wall. Drainage water must therefore be drained away as shown in Figure 9b. Connection of flashing to concrete walls is shown in Figure 9c. Ridge and bevel ¢nishing The type of ridge flashing should be selected according to the type of roofing material and the local climatic Figure 9a Recommended design of roo¢ng against a wood frame wall 49
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Building envelope performance asses
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Lisø, K.R./ Building envelope perf
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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
Page 49 and 50: LisÖ et al. construction industry
Page 51 and 52: Research in Building Physics, Carme
Page 53 and 54: 4 CLIMATE CHANGE SCENARIOS FOR NORW
Page 55 and 56: with large amounts of precipitation
Page 57 and 58: will most likely be worse, even wit
Page 59: Graves, H.M. & Phillipson, M.C. 200
Page 62 and 63: 766 Nordvik and Lisø The topic of
Page 64 and 65: 768 Nordvik and Lisø into the futu
Page 66 and 67: 770 Nordvik and Lisø climate chang
Page 68 and 69: 772 Nordvik and Lisø 0 Â Â = p d
Page 70 and 71: 774 Nordvik and Lisø probably to a
Page 73 and 74: BUILDING RESEARCH &INFORMATION (200
Page 75 and 76: cost of repairing process-induced b
Page 77 and 78: change in quality (Mehus et al., 20
Page 79 and 80: on the impacts of different climati
Page 81 and 82: different strategies: risk-based, p
Page 83 and 84: Lisø, K.R./ Building envelope perf
Page 85 and 86: Learning from experience - an analy
Page 87 and 88: An important aspect of the programm
Page 89 and 90: Concrete walls 32 % LECA masonry 10
Page 91 and 92: construction industry, and academic
Page 93 and 94: BUILDING RESEARCH &INFORMATION (JAN
Page 95 and 96: greater variations (Lisø et al., 2
Page 97 and 98: Typical problem areas and recommend
Page 99: Figure 3b Recommended design of win
Page 103 and 104: Figure 11a Poor solution for a £as
Page 105 and 106: Acknowledgements This paper was wri
Page 107 and 108: Climate adapted design of masonry s
Page 109 and 110: 2. Masonry defects in Norway 2.1. S
Page 111 and 112: Fig. 2. Example illustrations of th
Page 113 and 114: The presented results are in good a
Page 115 and 116: appropriate in a more severe type o
Page 117 and 118: screen in a two-stage weatherproofi
Page 119 and 120: INCREASED SNOW LOADS AND WIND ACTIO
Page 121 and 122: The hurricane (Beaufort number 12)
Page 123 and 124: The extensive revisions of the code
Page 125 and 126: The number of buildings investigate
Page 127 and 128: As is apparent from the values in t
Page 129 and 130: climate change is now dominated by
Page 131: TABLE 3. Summary of findings Struct
Page 134 and 135: Lisø, K.R./ Building envelope perf
Page 136 and 137: temperature of -4°C or less. See F
Page 138 and 139: Today, frost resistance of brick, c
Page 140 and 141: degree of saturation, freezing will
Page 142 and 143: accelerated frost damage or frost d
Page 144 and 145: A possible objection to the present
Page 146 and 147: [17] Dührkop H., Saretok V., Sneck
Page 149 and 150: 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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Lisø PhD Dissertation Manuscript - NTNU

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