What are SIPs?

SIPs or Structurally Insulated Panels consist of two outer layers of Oriented Strand Board (OSB) sandwiched around an Expanded Polystyrene (EPS) foam core. Each composite panel is robust, lightweight and extremely strong – up to seven times stronger than a timber frame. SIPs are incredibly well insulated and airtight, resulting in a structure that required less energy to heat and one that provides better air quality for the user.

SIP panels have been used in the USA, Canada, Japan and Europe since the 1950s where they have become a mainstream building material for constructing homes. Now, SIPs are becoming increasingly popular here in the UK.

Building with SIPs as the structural element for property walls, roofs and suspended floors is quick, easy and cost-effective. Timber splines between the panels ensure a structurally-sound framed system with panels fixed to the footings via a timber sole plate and to the ceiling via a timber ring beam. There’s no risk of the compression shrinkage or cold bridging that is normally associated with stud walls and other traditional methods.

Recommended panel options

 Garden Office (-30m2)Garden Annex (+30m2)House
Floor thickness96mm172mm-
Wall thickness96mm172mm172mm
Roof thickness120mm172mm222mm
Floor U-Value (thermal resistance)0.380.19-
Wall U-Value (thermal resistance)0.380.190.19
Roof U-Value (thermal resistance)
Floor EPS insulation74mm 150mm150mm
Wall EPS insulation74mm 150mm150mm
Roof EPS insulation98mm150mm200mm
OSB thickness11mm11mm11mm
Max panel width1.2m1.2m1.2m
Max panel length3m3m3m

Considering SIPs for your next project?

Panel components

Our SIPs use 11mm Sterling Board OSB3 skins as standard. Sterling OSB3 is a precision-engineered structural board that is an industry recognised as a structural material for use in load-bearing conditions. Sterling OSB3 is BBA approved and conforms to Eurocodes. Sterling OSB3 is also FSC® certified and made from timber grown in the UK. It is manufactured here too, meaning fewer carbon miles are clocked up during transportation.

For the foam core of our SIPs we use BBA accredited, 70 Grade EPS. EPS is non-toxic and biologically inert. Containing a flame-retardant additive, it has a reaction to Fire Class E, a high strength-to-weight ratio and very low thermal conductivity (W/mK, at 10°C) of 0.032. EPS does not, and has never, contained either CFCs [chlorofluorocarbons] or HCFCs [hydrochlorofluorocarbons] gases, which diminish the ozone layer. EPS is fully recyclable and no waste is created in its manufacture. Expanded Polystyrene (EPS) is one of the few building materials that can truly claim to be 100% recyclable. It can be reused in the manufacture of new EPS products, soil improvements and auxiliary compost material, as well as being added to other building materials. Also by fusion and granulation, it can be turned into simple products such as coat hangers and pens.

We laminate the OSB3 skins and EPS foam together to form SIPs using polyurethane glue and leave to cure under pressure in our press. Polyurethane is incredibly strong and once cured, the three layers that get laminated together create a SIP panel that can withstand incredible stresses. To see just how strong SIPs can be under extreme pressures, we recommend you watch this short video clip.

The timber used to create the outer skins and structural framework of our SIP panels come from FSC accredited plantations. We used C24 grade, tanalised structural timbers for stud work, splines and framework. Timber is naturally low in thermal conductivity, it’s 15 times better as an insulator than concrete and 400 times better than steel.