How do SIPS and ICF compare?

I don’t know whether to build with insulated concrete formwork (ICF) or structural insulated panels (SIPS). How would you say they compare in regard to costs and time of installation on a standard build?

e exact cost of using a particular structural system will depend on factors such as the design of your house and how you intend to manage it to the stage of completion. Some project profiles will be particularly suited to timber frame or SIPS

(see www.self-build.co.uk/sips), for instance – perhaps because you might want a quick, cost-certain route to weathertight stage and an easy path to good airtightness.

As a rule of thumb, on a standard house you might pay around 5% more to build using a modern structural system such as ICF (see www.self-build.co.uk/icf ) or SIPS compared to using masonry or timber frame. at’s largely down to the fact they’re not as widely-used as other methods– so there are fewer suppliers and specialist installers available.

However, there may be aspects of your project that make a modern system more attractive to you. Say you wanted to achieve Passivhaus standards for energy efficiency; in this case, using SIPS or a highly prefabricated form of timber frame might suit you. is is because it’s easier to achieve good airtightness (with less reliance on the site operatives to get this right). Design elements can lead you down a certain path, too: SIPS can make it easier to create features such as vaulted ceilings and ready-made rooms in the roof space.

It’s a similar story with ICF: it’s quicker to build with than standard masonry, although typically it is not as fast as timber frame or SIPS. And if your project profile fits well, then it will be extremely cost-effective. What’s more, as the polystyrene blocks get pumped with concrete, you end up creating a monolithic structure with impressive insulation and airtightness built in – so it’s also a very good choice for energy efficiency in use.

When we were designing the Build It Education House (www. self-build.co.uk/ourhouse), we wanted a basement. ICF is the simplest and cheapest system to make fully waterproof belowground, so it proved to be a very affordable choice on our build. Plus, it’s technically possible to build on a DIY basis with ICF with a little training from the supplier, which obviously can net big savings compared to using a contractor.

If you want to take the DIY route, you do need to be very confident in your skills. I would not recommend doing it yourself when it comes to something as sensitive as a basement build (unless you’re already a waterproofing expert).