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Building Products July 2017

DOORS, WINDOWS AND ACCESSORIES Hence the survey referenced earlier, which was carried out in 2013 and published in 2014, by the now-defunct Zero Carbon Hub. The Hub was created to help all new homes to reach some definition of carbon neutrality by 2016, a mission that would later be abandoned. The changing political landscape means that the Zero Carbon Hub is no longer in business, closed in March last year. However, the installation issue is still a current one: More Homes, Fewer Complaints, published by an all-parliamentary working group last year highlighted the problem of excessive defects in new-build homes. Outside Scotland and south west England, where frames are mostly fitted into a check reveal, the most common error made when installing windows is to place them too far forward. The window frame should be sitting so that it partially overlaps the cavity between the skins of the wall, creating a continuous higher U-value barrier to heat loss. In new build environments, the instinctive place to install a window seems to be so that the back of the frame is flush with the inside face of the outer brickwork. This also happens in replacement installations too. Yet this positioning can lead to the creation of the dreaded thermal bridge. Omission of a cavity closer around the window location is another frequent cause of poorer performance. And not all cavity closers are created equal; choosing one with a PU or PIR core gives higher levels of insulation. According to the NHBC, some installers are 48 BUILDING PRODUCTS | JULY 2017 still failing to seal the gap between window and opening. As well as creating a pathway for the escape of heat, poor sealing can also lead to noise problems. Good quality trims, silicants and sealants are vital but so too is attention to detail when they are being installed. Some specifications are calling for an additional EPDM fitted to the exterior of the window, lapping onto the cladding of the building; pre-treatment of any surfaces and using the right solvent is important in this situation. Though it is not the domain of the window installer, another error is caused by the treatment of the jambs. Insulated plasterboard on the reveal rather than standard plasterboard significantly reduces heat loss. As with jambs, problems with window installations are not solely the domain of the installer. The Zero Carbon Hub found that there was a ‘disconnect’ between those carrying out the conceptual design, those carrying out the detailed or working designs and those who were installing the windows and doors. The result of this can be details that do not make sense resulting in RFIs (request for information) being sent to the designer, or simply creating a detail there and then on site. Time pressure is always the strongest force – waiting for an answer can be considered too costly. The spread of BIM (building information modelling) should help address this issue: we know from the increasing number of downloads from our BIM Centre that its use is on the rise. Creating a 3D model before the physical one actually flags up interface and detail issues and may encourage earlier involvement of suppliers in the design process, avoiding those ‘by others’ notes so frequently found on architect’s drawings. Sometimes the problem is even more basic: drawings are not being used on site at all either because they do not exist or have not reached the window installer. The installers and supervisors use their past experience and instinct, yet this may lead to the thermal bridging issues already mentioned. When there are problems with the way windows are installed it is easy to blame poor workmanship and bemoan skills issues among the workforce. However, the reasons are more complex than that. We need to improve knowledge and competency in all the roles which impact on window selection and installation. Chris Coxon is Head of Marketing at Eurocell <<< Continued from page 47


Building Products July 2017
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