In Focus: SIPs

The owners of this SIPs self-build chose the system for its design flexibility, low wastage and insulative properties. The SIPs have been strapped and sheeted with 100mm cavity and 100mm blockwork. Read more about this project.

"I’m thinking of using SIPs (structural insulated panels) to build my four bedroom home, as I’ve heard the system offers high levels of insulation, airtightness, and a fast build route. However, can I insure a SIPs house? More importantly, I’m worried about the longevity of SIPs. I don’t want to be a guinea pig for a system which is not ‘tried and tested’ like masonry."

Mark Brinkley says: SIPs (structural insulated panels) are formed as solid panels of insulation – either expanded polystyrene or a type of polyurethane – sandwiched between two rigid boards which, combined, makes panels very strong and durable. As you mention, they also provide excellent insulation and airtightness — two qualities required for a low-energy house.

SIPs are an off-site construction system. The structure is built in a factory, taken to site on the back of a lorry and erected (very quickly) with the aid of a large crane. In this respect, they share many of the same benefits as timber frame building methods. Where SIPs differ from timber frame is that insulation is already built into the structure — meaning an extra task is removed from the build process. Where this really comes into its own is in the roof structure, which is much simplified with SIPs. Instead of building up a conventional roof or a series of roof trusses, SIPs can be simply laid across supporting beams. This is ideal for creating living space in the roof.

Would you be a guinea pig? Hardly. The first SIPs house was built in the US state of Wisconsin in 1937 and is still being used. Since then, hundreds of thousands of SIPs homes have been built around the world in all kinds of climate zones, withstanding hurricanes and earthquakes much better than most traditional building forms. SIPs have proven to be durable and robust.

In Britain, SIPs homes first appeared in the 1990s and there has been a steady trickle ever since, including a number of self-builds. Cost has been the main factor in SIPs not being more widely adopted. However, the cost differential between SIPs and the more conventional construction forms is getting smaller as legislation drives insulation levels ever higher. Some now question whether SIPs are any more expensive at all. Indeed, Custom Homes now offers its standard range of homes with SIPs at no additional cost.

If SIPs have a weakness, it is that the timber elements are susceptible to rot. For this reason, standard SIPs are not recommended in flood-risk areas. Having said that, the risk is no different to timber frame housebuilding in general, and the timber elements in masonry homes. Experienced designers know how to detail for this correctly: one of the key things to look for is that the external cladding (be it walling or roof cover) is effectively isolated from the internal load-bearing structure.

What about insurance and warranties? All the main suppliers are able to offer latent defect warranties on their build systems. This means that any SIPs-built house will be recognised by insurance companies and by Building Control. There should, therefore, be no difficulties in either insuring the finished house, or selling it on.

A new development in the growing SIPs market is the formation of a trade organisation to act as a mouthpiece for the British SIPs industry. Details of the members – and a good place to look for suppliers – can be found at uksips.org.

Further reading:

• Read more from Mark Brinkley in his blog
• Are SIPs the best choice for your self-build project?
• A SIPs Self-build