Structural insulated panels (SIPs): pros and cons

What a SIP is

A SIP is a sandwich: a core of rigid foam insulation between two structural facings, commonly oriented strand board (OSB) or another board material. The panels are made in a factory to the size needed, with openings cut for doors, windows and services, and are delivered to the site and fixed together with splines, timber and sealants.

What they do well

• Speed. Large panels go up quickly and make the building weathertight early.
• Insulation and airtightness. The foam core is continuous, and the panel joints can be sealed to make an airtight envelope.
• Accuracy. Factory cutting gives accurate openings and fewer on-site errors.
• Less waste. Cut-to-size panels can reduce site waste.
• Open interiors. The panels can span between supports, which can allow open-plan layouts and loft rooms.

A SIP is a sandwich: a core of rigid foam insulation between two structural facings, commonly oriented strand board (OSB) or another board material.

Cautions

• Moisture. The facings and joints must be protected from water, both during construction and in use. Leaks at joints can damage the facings, so flashing and membranes are essential.
• Fire. The foam core is combustible. Fire design, linings, cavity barriers and external wall rules must be checked for each building and country.
• Design before manufacture. Changing a panel on site is difficult, so the design must be fixed and coordinated early, including services.
• Airtightness and ventilation. An airtight building needs a planned ventilation strategy. See Airtightness and ventilation.
• Thermal bridging at joints. Splines and edge timbers should be detailed to avoid cold bridges. See Thermal bridging.
• Skills and supply. Look for experienced installers and for a supply chain near the project.
• Warranty and insurance. Lenders and warranty providers may have specific requirements.
• Carbon. Consider the carbon of the facings, foam and adhesives with other options. See Embodied carbon in plain language.

Where it fits

SIPs suit new houses, extensions, small offices and community buildings where speed and performance are priorities, and where the design is simple enough to be made in standard panel sizes.

In short

SIPs are fast, airtight and well insulated. They need careful design before manufacture, good moisture and fire detailing, and experienced installation.

See also: Timber frame construction explained and ICF vs. cavity wall vs. timber frame.

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