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RCI March 2018

Project1_Layout 1 07/05/2013 FLAT ROOFING & WATERPROOFING SYSTEMS The importance of condensation control in building structures Nik Ullfors, national technical manager of Visqueen Building Products, explores some of the recent developments in membrane technology for protection against condensation within building structures, and avoiding both performance issues and potential health issues During these cold winter months many of us have seen condensation occurring within our homes, usually in the form of dew on the inside of windows on a particularly cold morning. But what happens if condensation occurs within the fabric of a building? Condensation occurs when air reaches its maximum potential limit of carrying water and this limit depends on the temperature of the air carrying it, so when there is a temperature difference, say a cold window surface in a warm room, the water carrying limit of the air in contact with that surface is reduced and condensation occurs. In addition, warm, moist air will also travel towards areas of cooler, dryer air. So, when there is a temperature difference within a wall structure, this results in that warm, moist air permeating through the internal wall towards the cooler areas. If the temperature difference is high enough the dew point, (the point at which air loses its ability to hold more water) will lay somewhere within the internal structure. This can cause 076 MARCH 2018 RCIMAG.COM components leads to corrosion and decay of the building fabric, timber frame buildings and metal section internal frame are especially vulnerable, moreover in the case of insulation damage as this can reduce its thermal performance, exacerbating the problem. Alongside these potentially serious structural concerns are potentially serious health concerns for the people inside buildings where interstitial condensation occurs. The build-up of moisture in a wall structure creates damp conditions and thus mould and mildew can become present. This has implications for the health of people inside these buildings, especially homes. The presence of and living in proximity to mould can lead to the developing of respiratory problems, such as coughing and wheezing, and can lead to further chronic respiratory illnesses such as obstructive lung disease. All occupants can be affected, however, very young children and the elderly are the most vulnerable groups. Combat interstitial condensation Improved ventilation both in the building problems both for the building itself and the people inside it. This condensing of water into wall structure and within the internal rooms can help with directing moisture and air channels out of the building, reducing the amount of moist air that permeates through the wall. Increasing heating within a room can also help by moving the point at which it is cold enough for water to condense closer to the exterior wall and away from the internal wall components. This method can be expensive and not so environmentally-friendly so a more permanent solution is needed. This is where vapour control layers come in. Vapour control layers (VCLs) or barriers when placed within the warm side of a wall help prevent warm, moist air from penetrating to a point where it will condense. VCLs must conform to industry guidance such as BS5250:2011 code of practice for control of condensation in buildings: and NHBC chapter 6.2. Choosing the correct type of VCL can be very complex, as the VCL is incorporated into the fabric of the building so correct product selection at specification stage is paramount. The detailing of the membrane can be complicated too, therefore having a manufacturer on-hand who can provide expert technical support should be part of the design team. Standard details and bespoke details will assist the designer and on-site installation team. Applications where high humidity is a regular occurrence, such as swimming pools, hydrotherapy pools, and laundry rooms provide additional technical challenges. A high-performance VCL will be required for these demanding applications, for example, the VCL may contain an aluminium lining to reduce vapour transmission and the membrane will potentially be reinforced for additional strength. All VCL’s must survive the on-site installation phase, so consider the strength of the membrane, however, the VCL membrane should remain fl exible for ease of installation. Fully sealed taped joints at roll lap ends are required, in addition, all termination junctions must be fully sealed. The majority of VCLs in the UK market are loose laid sheets, and therefore, in vertical applications, the VCL will need adhering to the structure. The use of a suitable double-sided tape is therefore required. Vapour barriers serve as a long-lasting solution to the problem of interstitial condensation, preventing damage to internal structural elements, maintaining the thermal performance and effi ciency of a building, and protecting inhabitants from the damaging health efforts of mould and mildew. Differing vapour-resistances across a range of barriers provide versatility to meet the needs of different buildings, from protecting the structure of professional highmoisture environment facilities, to making sure a home is kept warm and safe to live in. Careful assessment of what is available will be time well spent in ensuring the best and most appropriate solution is specifi ed for each building’s condensation control requirements. V apour barrier systems prevent damage to internal structural elements, whilst maintaining the thermal performance and effi ciency of a building


RCI March 2018
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