It may not sound like the most progressive building material, but mix it with an insulating formwork and you’ve got a solid, energy efficient and speedy building system. What’s more, ICF lends itself to pretty much any design. From curved towers to barn-like dwellings, ICF can master the style.
ICF is based on hollow block or sheet components, usually made of polystyrene, fastened together with metal or plastic connectors. The panels or blocks lock together without bonding materials to provide a formwork system into which concrete is pumped.
Walls are generally constructed to first floor level before filling with concrete, letting it dry and going up to the other levels or roof. The formwork remains in place, not only to shape the walls, but also to provide a robust layer of thermal insulation – one that will last for the lifetime of the building.
The formwork bestows fantastic U-values ranging from around 0.30 W/m2K right down to around 0.11 W/m2K – perfect for the more stringent Building Regulations due in October, and the higher levels of the Code for Sustainable Homes. The structures also have very low air infiltration rates, almost all of which are accounted for by window and door openings. Consequently there is very little heat loss, which further boosts thermal efficiency.
ICF is fast to build with and requires less in the way of traditional building skills when compared to brick-and-block and even timber frame projects. In most cases, a four-room ground floor can be erected in just a couple of days. Only a small team of semi skilled (to around NVQ level 2) operatives is needed to put up the basic structure – which will save money on time and labour.
Most ICF firms in the UK run training courses to bring you up to the right level of competency to help construct the house yourself. And, as the insulation and structure are all completed in a single process, the homeowner inevitably saves time and expense on this too.
Design and finish
While it is easy to spot the construction system used on many homes, it is nearly impossible to tell an ICF house from a masonry or timber frame project. This is because the system is ultra flexible design-wise. The blocks can be used for creating curved walls, arches and irregular angles – you can build in any style, to virtually any dimension.
It’s easy to construct bay windows, circular portholes and doors too, as they can be integrated into the building envelope and internal walls, eliminating the need to specify specialist products.
The polystyrene blocks or sheets give a uniform and smooth surface that is ready to take most forms of internal and external finish. Externally you can clad ICF with a myriad of materials. Many ICF homeowners opt for some sort of coloured flexible render, as it works really well and can be applied directly onto the polystyrene. You can also choose more conventional finishes such as brick slip, stone facade or weatherboarding depending on your design.
What to bear in mind
Although ICF sounds like simplicity itself, there are a few things to bear in mind if you choose the system. The pour stage is critical – the ready-mix has to be of the right consistency to flow to all parts of the formwork, and the system must be braced to exacting measurements, or else walls could distort. The concrete has to be poured in slowly and steadily or there is a risk of the forms bursting open. Obviously mistakes do happen, but an experienced operator will be able to resolve any problems.
Adapting the house in the future – adding doors and windows, or moving their position – can be fairly difficult, although not impossible using specialist tools. The concrete frames offer a whole floor space without further loadbearing walls, so you can remodel floor layouts.