The Swedes routinely test their triple-glazed windows for sound reduction and specifiers with external noise issues may well find these windows fit the bill.
Whereas a double-glazed window achieves sound reduction of around 25-30dB, a triple-glazed window will achieve 30-40 dB. The main Swedish manufacturers produce a 2+1 unit which consists of a double glazed sealed unit and a third pane of glass on the outside, separated by a 50 mm air gap. This extra gap is particularly effective in reducing high frequency sounds and some designs claim a 45dB sound reduction.
Very low-U "The Swedes have developed techniques for deadening sound, experimenting with different air gaps and using materials such as laminated glass. Very low U values and very high sound reduction are possible in the same windows but of course they come at a price," says Jerry Chalder of Scandinavian Building Products, importer of SP Fonster windows.
UK volume joinery manufacturers have not embraced triple-glazing. Bill Dunster, architect of housing association Peabody Trust's Beddington Zero Energy village in Sutton, Surrey, has been looking for suitable window suppliers for this ultra-green project. "We tried extremely hard to secure a UK supplier of the right size and at the right price, but at the moment there isn't anyone to fit the bill," he says. "For the performance we need, at a price we can afford to pay, we have to go abroad." Swedish joinery giants Elite and SP Fonster produce triple-glazed windows as catalogue items and are keen to expand into the UK market. These are usually offered as either straight timber or timber clad with aluminium.
"We tend to find that the aluminium claddings are preferred on commercial projects while the domestic sector prefers to use timber," says Mark Modine of UK importer, Swedish Instant Windows.
"Obviously for a project like Beddington, PVC was not an option. But I have reservations about aluminium exteriors bonded onto a timber base. In many cases they are unable to guarantee such designs for any longer than ten years. I think that the modern generation of microporous high build window stains are an excellent product which will outlast the other alternatives, given the correct maintenance regime," says Dunster.
But there are considerable thermal advantages to triple-glazing. While UK-style double-glazing achieves a U value of around 1.8, the Swedes are achieving U values as low as 1.1. The second air break in triple-glazing is part of the reason but there are other refinements including the use of superior low-E coatings and the substitution of krypton gas for argon in the units.
Security is another issue. Secured by Design standards, based on BS 7950, are becoming more widely known and RSL clients are beginning to insist on joinery which fulfils these standards.
Security concerns "What we specify and what we get to build are often quite different," says Peter Chlapowski, partner of PCKO Architects. "Ideally we would like our clients to use timber, preferably from a certified source, with low-E, argon filled double-glazed units with a 20 mm air gap. However, these days our clients seem more concerned with security standards and this greatly limits our choice of windows.
"There are good products from small producers which don't meet security standards because of the prohibitive expense of having them tested." Dunster also acknowledges the problem. "I don't think security should be dealt with at the specification stage, it needs to be addressed by overall design and management." However, with the new Part L of the Building Regulations only looking for U values of around 1.8, Swedish windows promising U values down at 1.1 may seem of academic interest only. But sound insulation and security concerns may yet change habits.
Source
Building Homes
