Industry buzz suggests that structural insulated panels (SIPs) are the future of timber building. Why? Because not only do they utilise sustainable materials and minimise waste, they create ultra efficient homes too. Furthermore, as all new homes must be built to higher efficiency standards when building regulations change in October 2010, it makes good sense to put thermal performance and energy efficiency at the top of your list of requirements when choosing a construction system.
SIPs are composite panels used to create a building’s structural loadbearing elements. The panels consist of two layers of oriented strand board (OSB) sandwiching an insulation core typically made up of either expanded polystyrene (EPS) or polyurethane (PU). The composite structure is much stronger than the sum of its parts, with the insulation core stabilising the OSB and preventing deflection under loading.
SIPs are similar to panelised timber frame in that they are prefabricated off site in a factory. The use of Computer Aided Design (CAD) technology ensures that every panel is precision cut, so they are always straight and true, and little to no construction waste is created.
The panels, which are usually over a metre wide and a storey high, can be erected quickly and interlock securely to adjoining roof or wall panels. To ensure no air or heat can pass between them, panels are jointed with sealant and splines of OSB. Specialist fixings are also required and expanding foam is used to seal any gaps.
Construction is made simpler still as window and door openings can be pre-cut, and the inside is battened to accept plasterboard while leaving gaps for the electrics. Together these elements provide a quick on site construction time, especially in getting to the watertight stage, meaning various subcontractors can get a head start on other work.
The lightweight nature of the panels can lead to a reduction in foundation loadings, giving the structural engineer flexibility of design, and often meaning a reduction in groundwork costs. This makes SIPs ideal for adding to existing structures, such as converting bungalows into two storey houses. Other applications include building a structure inside an existing shell for conversion projects, as infill panels for timber frame, or to create liveable roofspace.
Once the shell is complete, the external walls can then be finished in a huge variety of ways to create a traditional, contemporary or fusion aesthetic. Common finishings include traditional cavity and facing brickwork, timber cladding, brick slips and render systems.
What are the eco benefits?
Compared to some more conventional build methods, SIPs provide extremely thermally efficient, airtight homes. “With the government’s commitment to lowering CO2 Emissions in construction, together with numerous announcements that all new homes will be zero carbon by 2020 – plus the launch of The Code for Sustainable Homes in May of 2007 – thermal insulation and lower air leakage requirements within dwellings will increase dramatically,” says Andrew Orriss of the UK SIP Association. “By adopting the use of SIPs, these new requirements can easily be achieved, especially when the SIPs provider is integrated early enough in the design process to allow efficient and effective design.”
The method’s superior insulation levels offer a huge benefit in terms of space heating – SIPs homes require very little – which means that the system lends itself perfectly to eco-heating systems that have low output temperature.
“The composite nature of SIPs provides an efficient and effective solution to reducing thermal losses and therefore improving energy conservation,” says Orriss. “SIPs offer the efficiency of structural and thermal performance within one product. U-values as low as 0.11 W/m2K can be achieved through the use of SIPs whilst also limiting the increase in building dimensions (wall thickness).”
The resultant homes are draught-free, warm in winter and cool in summer – which drastically reduces energy consumption and carbon dioxide emissions for the lifetime of the building.
“The main benefit of SIPs over other panelised forms of construction is due to the limited quantity of repeating thermal bridges such as studs and noggins. Therefore a typical value of 94 per cent of the panel area is counted as insulation when calculating the U-value of building components,” says Orriss.
Main image: A member of Potton's site team erects first-floor SIPs wall panels