Insulating concrete formwork (ICF) for self builds

What is insulating concrete formwork (ICF)?

Insulating concrete formwork consists of hollow polystyrene panels or blocks that fit into each other (like LEGO). Concrete is then poured into them to create a solid structure. The polystyrene elements form the shape of the walls, as well as providing insulation.

Insulating concrete formwork on Grand Designs

You may have seen ICF on Grand Designs. where Kevin Mc Cloud describes ICF as a ‘quick and elegant’ build solution.

How much does it cost to build an ICF house?

This particular Grand Designs ICF house, at the Graven Hill custom build site cost £625,000 to build.

Generally speaking an ICF house will cost around 5% more than a traditional timber frame house.

Advantages of insulating concrete formwork

• It’s quick to construct.
• Low labour costs due to ease and speed of assembly. It doesn’t require specialist skills to install it.
• It can be erected in poor weather conditions. This allows you to push through with your project during all seasons and achieve a water-tight structure quickly.
• Direct placement of ready mix concrete reduces waste and reduced need for on-site storage of materials.
• Good performance for:
  • fire resistance
  • thermal performance
  • airtightness
  • flood resilience
  • acoustic insulation.

How long does it take to build a house with ICF?

It’s usually much quicker than traditional methods, such as brick and block or timber frame. Formwork for a house can go up in just a couple of days, with a few more to strengthen and brace as needed. The concrete pour can usually be done in a day.

What is the U-Value of ICF?

anything from 0.30 W/m2K down to 0.11 W/m2K, so it well surpasses Building Regs requirements

Disadvantages of insulating concrete formwork

• Walls tend to be very thick, so it may not be the best solution on a small plots e.g. in urban areas.

Does insulating concrete formwork need reinforcement?

Not always, but sometimes yes. It will depend on the required structural performance in a given situation. Your structural engineer can advise on this.

Can insulated concrete formwork be used in curved walls?

Yes! It’s very flexible. There are a variety of shapes that exist to create many different forms.

What finish can I use for ICF

Render is a common finish for ICF, but the options are endless. it can be clad in virtually any finish. Internally it can be dry-lined and plastered or tiled.

Types of ICF

They come as either blocks or panels, and can be either extruded polystyrene or expanded polystyrene.

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