INSULATION AND ACOUSTICS should be between 0.5 and 1.5 air changes per hour. This includes controlled and uncontrolled ventilation. When considering the airtightness of a building, moisture management should also be taken into consideration. All air contains moisture, which is measured as relative humidity. In a healthy internal climate, the relative humidity is typically between 40-60%, although bathroom and kitchens often exceed these levels. There are a number of contributing factors to a building’s moisture levels, including the building fabric itself, if there is considerable construction moisture present following a building’s completion; as well as occupant activities such as showering, cooking and laundry; and leakage from rainwater, groundwater and plumbing. Any moisture accumulation within a property can be harmful to a building. It can cause timber damage and rot, corrosion of steel and concrete reinforcement, damp and mould growth and a reduction in the insulation performance. With the above in mind, the correct specification (and subsequent installation) of an airtightness and moisture management membrane is key to minimising the accumulation of moisture in the building fabric. A traditional vapour control layer (VCL), such as Prisoners build a new career with off-site insulation installation 32 BUILDING PRODUCTS | MARCH 2018 a polythene sheet, can create an airtight finish and block any moisture transport by diffusion. However, in practice it is very difficult to create a completely airtight finish using a VCL; it also does not allow any moisture that is trapped within the structure to dry out. As such, we have recently seen the development of a ‘smart’ or ‘intelligent’ membrane, which offers active moisture management as well as zero air penetration (when correctly installed). The membranes are ‘smart’ because they react to its environment, providing a moisture barrier during cold periods with high internal humidity, but then allowing the building fabric to dry out in warmer seasons, when internal relative humidity is typically low. This results in a lower risk of interstitial condensation. Smart membranes are able to vary resistance to moisture transport by diffusion. For example, in <<< Continued from page 31 winter, the pores in the membrane close to increase the diffusion resistance and moisture inside the building is prevented from moving into the structure. In summer, the pores in the membrane open so that the moisture, which has built up within the structure can escape, preventing damage to the building. In fact, some smart membranes allow the building envelope to dry out by up to 340g/m² of water per year. What’s more, as well as the membrane being more intelligent in terms of performance, the installation can be a lot easier and quicker. Undeniably, by helping to increase thermal performance and putting a stop to unwanted moisture build-up in a property, smart vapour control layers help specifiers and housebuilders to deliver comfort and well-being to building occupants, as well as more robust building structures. www.isover.co.uk/vario. Smart membranes are able to vary resistance to moisture transport by diffusion Smart membranes are able to vary resistance to moisture transport by diffusion AManchester-based steel frame construction specialist is offering prisoners a chance for a new career building homes insulated with Actis Hybrid insulation. Osco Homes has been working with inmates at HMP Hindley in Wigan for some years, helping them to develop skills required for future employment through training and mentoring. Each inmate starts the training within prison and, on completion, will be supported into full time employment, helping to reduce re-offending and deliver what Osco describes as ‘significant benefits to the public purse’. Until recently, Osco used other forms of insulation for its homes – until operations manager, Karl Ventre, stumbled across a YouTube video, showing how to install Actis’ honeycomb insulation, Hybris. Karl explained: “I saw the video via a LinkedIn feed and thought the Hybris panels looked a doddle. The Osco’s operations manager, Karl Ventre, made the switch to Actis’ Hybris prisoners had been complaining that the mineral wool we had been using was itchy and uncomfortable to work with. Obviously, we wanted to do something to eliminate this situation. And Hybris was absolutely the answer we’d been looking for. Not only is it not at all itchy, it’s very clean, there’s no dust, it’s incredibly quick and easy to install and very light, which is a nice contrast to our steel frames.” Much of the steel frame construction process is carried out, by the prisoners, off-site, before the components – insulated walls, roofs and floors – are lifted into place on-site. The construction of the first Osco Homes house to use Hybris consists of a floor, walls and roof structure insulated with 60mm Hybris, which is centrally fitted within the light gauge steel substructure. Osco Homes says it is a ‘great believer’ in the benefits of off-site construction in providing ‘not only high quality, energy efficient and attractive houses, but also a speedier way to build the homes the UK so badly needs’.
Building Products March 2018
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