What are SIPS and how do they provide the optimum fabric first solution?

Experts from the UK Structural Insulated Panel Association explain why the use of SIPS technology is on the increase across the UK.

Structural insulated panel systems (SIPS) are an advanced method of construction, offering superior insulation, structural strength and air-tightness. SIPS are used in floors, walls and roofs for residential, industrial, educational and commercial applications – providing ecologically friendly and energy efficient buildings.

SIP technology has been developed around composite panel techniques, creating a product with excellent structural and thermal characteristics. SIPS have two parallel faces – usually oriented strand board (OSB), sandwiching a rigid core of polyurethane (PU) foam or expanded polystyrene (EPS), making them lightweight, quick to erect and free from problems of compression shrinkage and cold bridging associated with other forms of construction.

SIPS and thermal performance
The construction industry has witnessed a significant rise in the use of SIPS for use in both residential and commercial buildings. In the UK 60 per cent of fossil fuels are used to heat buildings and half of this is housing. By far the most economical method of reducing fossil fuel use in housing is to reduce space heating demand, by focusing on more efficient building fabric solutions. SIPS have many of the answers.

Thermal resistance (U-values)
The thermal resistance of a material indicates its ability to transfer heat. In solids this is directly proportional to the material’s thickness since heat is transferred via conduction. Therefore, to improve the thermal resistance and reduce the U-value an increase in thickness of building elements is required.

SIPS offer the efficiency of structural and thermal performance within one product, delivering U-values as low as 0.11 W/m2k while also limiting the increase in building dimensions (wall thickness).

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 to BS EN ISO 8990.

Thermal bridging (Y-values)
Although repeating thermal bridges are accounted for within the U-value calculation, non-repeating thermal bridges require special consideration. Up to 15 per cent of heat loss from the building envelope combined with the associated issues of localised condensation and mould build up can be attributed to these localised cold bridges. Typically these occur around openings and junctions where there are gaps in insulation or materials of low thermal resistance are required for other envelope performance requirements. The introduction of the amended Approved Documents of Part L in April 2010 meant that heat loss calculations were replaced by the concept of Fabric Energy Efficiency (FEE) putting more focus on thermal bridges when calculating the Dwelling Emissions Rate (DER) and FEEs.

Part L has put increased focus and weighting on the airtightness of the building envelope – ‘build tight – ventilate right’ is the mantra that has been adopted. The flow of air through a building is either controlled through ventilation, or uncontrolled through air leakage.

SIPS – the future of low energy construction
SIPS provide a balanced approach to hygrothermal performance (the transfer of heat, air and moisture through the building envelope) that maximises gains in all areas without compromising others. The flexibility of SIPS permits a wide and varied building type and style with very little restriction on size, shape and form.

With the government’s commitment to the lowering of CO₂ emissions in construction, together with numerous announcements that all new homes will be zero carbon rated by 2020, thermal insulation and lower air leakage requirements will increase dramatically.

The Building Regulations consist of Part A to P, with Part L concentrating on the thermal qualities and energy efficiency of residential and commercial buildings. Part L 2013 has now been published and the approved document will be coming into force in April 2014.

There are now two targets to meet for houses – as well as the Target Emission Rate (TER) at six per cent reduction in CO₂ for residential and nine per cent for commercial, dwellings also need to meet a Target Fabric Energy Efficiency (TFEE) measured in kWh/m2/year.)

For architects and developers this improvement is achievable with good fabric and design. By adopting the use of structural insulated panels, 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.