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EXTERNAL ENVELOPE Fig 2. Microscopic view of airtight underlay
a non-ventilated roof strategy is adopted.” As for airtight membranes, Fairnington explains the building physics around why their limited vapour permeability means condensation can still occur: “If you have a big cold roof space and a sudden drop in temperature, you want to have air movement.” He adds, “People assumed that because they were installing a vapour permeable membrane, they didn’t need to ventilate their roof – but in certain circumstances moisture levels were too high or temperatures too low to allow the vapour to permeate without condensing.” By contrast, a high performance vapour and air permeable membrane has a far higher degree of vapour and air permeability and will still perform in conditions where airtight alternatives fail.
Crucial findings
Between 2001 and 2004, independent research on a cross-industry basis was carried out with Glasgow Caledonian University. The Partners in Innovation study was conducted to establish a consensus on whether it was still necessary to ventilate
“Roofing underlays come in different colours, but it’s what you can’t see
that does the work” Iain Fairnington
buildings where vapour permeable membranes were installed.
The study revealed the crucial finding that when a roof was unventilated while an air and vapour permeable underlay was used, this would further reduce and inhibit the formation of condensation on the underlay. This contributed to the NHBC making a statement in their Technical Extra bulletin Issue 6 that independently certified air and vapour permeable underlays could be used without additional ridge ventilation in cold roofs.
The evidence is clear for architects, house builders and contractors looking for a high performance, fail-safe roof that is cost effective – some air and vapour permeable underlays are in a class of their own.
Wallbarn Protecto-board
Wallbarn Protecto-board is the ideal product for flat roofing systems and is used to protect bituminous waterproofing membranes from mechanical damage during construction, protection from other trades and against abrasion and punctures. It is installed directly onto bituminous sheet membranes, hot melt and built-up membranes to give assurance against damage. Made from recycled fibres with at least 75 per cent per cent bitumen content, it is strong, durable and will not absorb water. It is extremely versatile and can be used as a recovery board, avoiding the need to take up existing surfaces before laying a new waterproofing membrane. It can be torch bonded to compatible membranes, spot bonded or taped and is useful as either a temporary protection or a permanent part of the waterproofing system. It is lightweight and easy to handle and is suitable for vertical surfaces where it will protect the membrane from ground settlement in the case of backfill.
For more information please visit the website and search for “Protecto-board”. 0208 916 2222
www.wallbarn.com
Axter showcase pioneering system FORCE DALLE at Victory Pier, Gillingham
Axter is proud to provide the waterproofing for Berkeley Homes’ prestigious Victory Pier, an award winning development in Gillingham comprising one, two and three bedroom apartments overlooking the River Medway. The development provides ample amenity space with green podium areas, balconies and terraces, creating luxury waterside living. Axter specified their pioneering FORCE DALLE system, a hybrid structural waterproofing system combining the proven benefits of hot melt with advanced bituminous membrane technology. Due to its versatility, FORCE DALLE offers a range of choices for designers and can be used in all roof construction types (warm, inverted, cold), on all structural decks (concrete, metal, timber) and can be combined with all roof finishes (green, brown, blue). The system was installed by Tilbury Contracts, approved Axtershield Installer, following the key steps: Prepare, Prime and Torch. Installation is quick and simple, and the result is a robust, reliable waterproofing system that is guaranteed for a minimum of 20 years. See how good working relationships, skills and expertise made waterproofing Victory Pier a success.
01473 724056
www.axter.co.uk
WWW.ARCHITECTSDATAFILE.CO.UK
ADF OCTOBER 2016
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