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Meeting the requirements of the Building Regulations – dwellings
Published in Ray Tricker, Samantha Alford, Building Regulations in Brief, 2022
Driving rain or wind-driven spray from the sea or other water bodies adjacent to the building can penetrate walls directly, or through cracks or joints between elements, and damage the structure or internal fittings or equipment. Surface condensation from the water vapour generated within the building can cause moulds to grow which pose a health hazard to occupants. Interstitial condensation (a form of structural damping that occurs when warm, moist air penetrates inside a wall, roof or floor structure, reaches the dew point and condenses into liquid water) may damage the structure. Spills and leaks of water, in rooms where sanitary fittings or fixed appliances that use water are installed (e.g. bathrooms and kitchens), may also damage walls.
Prediction Techniques
Published in Rodger Edwards, Handbook of Domestic Ventilation, 2006
The practical consequences of interstitial condensation taking place are dependent on the structure that is affected. Serious consequences are most likely to be observed in structures which include layers that are susceptible to water damage. A classic example is at the interface between insulation and plywood sheathing within a timber-framed wall construction, as shown in Figure 3.4. When condensation occurs, the water will soak the insulation, plywood and other timber. Under sustained exposure to high-moisture contents, mould growth will set in, with all the attendant risksfor structural integrity. In theory, the vapour barrier in the structure should eliminate the risk of interstitial condensation. The reality is that controls on the building process within the UK are such that many vapour barriers are not put in correctly. They may not be correctly sealed at joints between adjacent sheets or at detailing points such as doors, windows and light switches. In the worst cases, the membrane may have been perforated during the construction process. This was particularly true during the building boom of the later 1970s and early 1980s, when timber-framed construction enjoyed an upsurge in popularity. The problems discovered were so substantial that the use of timber-framed construction came to an almost total halt. Public confidence in timber-framed construction is still very low, and mortgage lenders are most reluctant to become involved in the purchase of any dwelling so constructed. This is, in the opinion of the author, a matter of some regret, since soundly constructed timber-framed dwellings, for example following the methodology described in advised by the Timber Research and Development Association (TRADA),9 offer great attractions in terms of speed of building, flexibility, energy efficiency and environmental impact of the construction materials used.
Flat roofs
Published in Duncan Marshall, Derek Worthing, Roger Heath, Nigel Dann, Understanding Housing Defects, 2013
Duncan Marshall, Derek Worthing, Roger Heath, Nigel Dann
Both cold and warm roofs should be designed to avoid interstitial condensation. Interstitial condensation occurs when warm, moist internal air from the building passes through the roof structure (because the internal air pressure is higher than the cold external air) and on meeting any colder air, or colder structure within the roof, the warm air condenses. (See Chapter 16, which discusses the principles of condensation in more detail.)
Energy retrofit infill panels for historic timber-framed buildings in the UK: physical test panel monitoring versus hygrothermal simulation
Published in Architectural Science Review, 2021
Christopher J. Whitman, Oriel Prizeman, Julie Gwilliam, Andy Shea, Pete Walker
For the initial three weeks of monitoring the test panels were subjected to steady-state conditions with the aim of forcing increased moisture content. To determine the set temperature and relative humidity of the test chamber, Glaser calculations were undertaken in accordance with BS EN ISO 13788:2012 (British Standards Institution 2012). These calculations plot the vapour pressure against the saturation vapour pressure, across the thickness of the panel build-up under steady-state conditions and constant heat transfer. Where the vapour pressure touches the saturation vapour pressure, interstitial condensation is deemed to occur. The results of these calculations (Figure 9) showed that with internal conditions of 21°C/70% RH and external of 5°C/80% RH, interstitial condensation would occur within the wood fibre panel, and the wattle-and-daub would see an increase in moisture towards its inner face.