What is a structural insulated panel (SIP)?
A structural insulated panel (SIP) is a load-bearing, insulating sandwich panel made of two structural boards, usually OSB/3, bonded to a rigid foam core of EPS, PUR or PIR in the factory. The panel acts as structure and insulation at once, so walls and roofs can be built without separate studs or rafters. SIPs are widely used in North America and are a popular system for self-build homes and extensions in the UK.
How a SIP differs from a standard sandwich panel
- Standard (composite) sandwich panel: usually steel facings with a PIR or mineral wool core, fixed to the steel or timber frame of a shed or industrial building. It spans between purlins or rails but does not carry the building’s floors.
- SIP: timber-based facings that, together with the core, carry the vertical loads from floors and roof. The wall is the structure, as in timber frame construction, but without a frame.
Panels are joined with timber splines or blocks set into rebated edges, then screwed or nailed and glued. Service chases are often routed into the core at the factory.
Application
- Get the design engineered. Spans, storey heights and fixings depend on the system; use the manufacturer’s design data and details, and check them with a structural engineer.
- Keep the OSB dry. Store panels off the ground and covered, make the building weathertight quickly and use a breathable membrane with a ventilated cladding.
- Seal every joint. Tape panel joints on the warm side. Leaky joints waste heat and can cause condensation inside the build-up.
- Deal with fire safety. The foam core must be protected internally, normally with plasterboard as specified by the manufacturer and building regulations.
- Plan services early. Cutting chases or large openings afterwards weakens both structure and insulation.
- Common mistake: treating a SIP like an insulation board and cutting in a roof window without checking the structural design.
Related terms
- Sandwich panel
- OSB board
- EPS
- PIR insulation
- Timber frame construction
- Insulation value Rd value
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