Many a SIP13 April 2006
SIPs are being heralded as the next generation of timber building systems, principally because of their thermal performance. Stephen Powney reports on this emerging technology
Timber frame construction is becoming an increasingly broad church as the number of options for developers, self-builders and housing associations seems to be constantly growing, sparked by technical leaps, tighter Building Regulations and a move towards greener materials.
Structural Insulated Panels (SIPs) are a good example of this, though they are not exactly a new technology. They have actually been around since about the 1950s in the US and since the 1970s in Britain. But SIPs are now becoming more popular, especially in residential construction, primarily because of their thermal performance.
SIPs can come in a variety of forms but usually consist of a core of rigid insulation bonded to two outer layers of OSB.
Sounds simple, doesn’t it? Yet the claimed benefits for the product include increased strength (anything up to six or seven times as strong as conventional timber frame, according to some SIP suppliers) lower U-values, improved air tightness and quick build time.
The lower U-value performance could prove to be the real advantage for SIPs, coming at a time of tightening Building Regulations concerning energy efficiency, especially the updated Part L (conservation of fuel and power) (see p66) which will come into force in April.
This thermal performance was demonstrated by Langley-based Maple Timber Frame during the recent launch of its SupaWall, a system which differs from other SIPs in that it also features timber studs in the structure.
When Timber Building visited Maple’s SupaWall house, it was a cold day and the house, like many newly-built homes, was empty. There was no central heating installed but the temperature gauges read 19˚C on the ground floor and 21˚C on the first floor.
Maple said this was because the insulated wall structure, tested by the National Physical Laboratory as having a U-value of 0.113W/m2K (including external cladding), kept the heat in. A heat recovery system in the loft redistributes heat generated in the house and also insures a continuous flow of fresh air.
The 140mm-deep SupaWall is injected with polyurethane foam insulation in Maple’s factory and incorporates a plasterboard-sheathed internal service zone.
Philip Price, head of Maple’s technical department, said: “As well as cutting heating bills, the system contributes to a reduction in the use of fossil fuels and CO2 emissions – and therefore to the government’s commitments on climate change.”
Wigan-based SIP Building Systems (SBS) is another company which sees great potential for SIPs in residential construction. The company manufactures blank panels for a number of SIP suppliers, including Scotland-based SIPit, Build It Green and SIP Build Ltd, which offer a design and fabrication service for clients. SBS general manager John Allan said the company had invested about £1m in its manufacturing facility and demand for the product was increasing.
SIP Build fabricates panels from its own 33,000ft2 facility on the same site as SBS. “The self-build market has embraced the technology,said Peter Barr, SIP Build director. “But we’re also now finding apartment developments and schools becoming a large market.”
Barr said the imminent introduction of updated Part L was influencing developers to trial various modern methods of construction, including timber frame, SIPs and steel construction systems. SIP Build, which has recently quoted to provide infill panels for a 13-storey apartment development, says its 150mm panels can achieve a U-value as low as 0.14W/m2.
German-made technology is making sizeable inroads into the SIPs market, through Kingpsan TEK. Its Berlin production facility has an annual production capacity of more than 12,000 houses, though currently 700-1,000 units are supplied across three markets – Germany, Ireland and Britain.
Its current projects include 550 units for the Lovell Partnership in Beswick, Manchester – reputed to be the UK’s single largest off-site development. TEK has already supplied 75 units in the first phase, with the second phase now under way.
The TEK product is based on a 140mm-deep panel, which achieves a U-value of 0.20Wm2K, which Jeff Tomlinson, Kingspan TEK’s national sales manager, said exceeds current Building Regulations requirements by 45%. Rigid urethane is used as the panels’ insulation core.
Tomlinson said SIPs’ similarities with timber frame include speed of construction and deskilling of the build process, ability to meet construction programmes and flexibility for the builder. Builders could “turn off the tap [supply of house kits] when they want”, he said, and wait for current developments to be sold without fear of losing skilled wet tradesmen.
Tomlinson described volume housebuilder and housing association business as “very good”, while it handles the self-build market through a national network of 10 suppliers, which design and fabricate standard TEK panels.
“Building contractors are usually driven by price versus performance,he said, “but if we can speak to the client directly we feel we can interest them in what TEK is all about – increased insulation, fewer draughts and reduced running costs. And as long as the product does not compromise the architect’s flair or design brief, then they are happy.”
TEK, which has just secured a second BBA accreditation for building up to four storeys, also supplies SIPs as infill panels to a number of green oak construction companies, and has seen growing business in room-in-the-roof applications due to PPG3 and the popularity of home offices.
Martin Milner, of specialist timber engineering consultants CCB Evolution, part of the Chiltern Group, said SIPs technology was becoming increasingly diverse, with different products boasting different structural and acoustic properties depending on the type of sheathing, insulation and adhesive materials used.
“Each needs to be assessed based on its constituent parts and also the vertical connectivity [how panels are connected together] and how the loads are transferred into the SIPs panel,he said. “You cannot assume the same properties as timber frame.”
He said SIPs could take higher loads than standard timber frame due to a larger load-bearing area. “But the strength of the SIP is not its selling point. It’s the thermal efficiency,he added.
Milner advocates third-party accreditation of SIP systems in the absence of any codes, except European Technical Approval Guideline 19, covering the build method.
“More and more contractors are realising SIPs’ potential. But one solution does not fit all – that’s a very important message. All products have an advantage, which must be identified for each project.