ICF Construction – What is Insulated Concrete Formwork & is it Right for Your Self Build?

From costs to design, Erika Chaffey investigates the benefits of insulated concrete formwork (ICF) construction, and takes a look at whether it could be the right fit for your bespoke home
by Erika Chaffey
15th January 2025

Insulated concrete formwork (ICF) is a modern method of construction, ideal for those looking to create a sustainable, energy-efficient and durable structure for their dream home.

But what exactly is ICF construction, how does it work and why should you consider it for your project? Here, I’m exploring its key benefits, what can be achieved with ICF and what to consider for a successful build.

What is Insulated Concrete Formwork (ICF) Construction?

This unique construction method uses lightweight hollow blocks or panels, typically made of rigid foam insulation, which are stacked to form your walls, floors and other structures. Once assembled, steel reinforcement is added where necessary, and the forms are then filled with concrete – creating a super strong, airtight and highly insulated building envelope.

Thanks to the system’s innate strength, you can build external walls, retaining walls, foundations, basements, and more with ICF. “It’s highly versatile and can be used to build almost any type of structure,” says Anthony Quinn, managing director at ICF Southern. So, it’s a great whole-build solution for those looking to incorporate a basement into their house design, for instance, as well as for simply creating stylish, energy-efficient modern homes.

Considering different build systems?

Once you have a plot, the next key decision is which build route is best for your project. Timber frame, ICF, brick, masonry, hemp, SIPs, CLT or steel frame? All have their benefits and downsides. At Build It Live you can speak to experts who specialise in building with these different systems and who can help you choose the best choice for you. Explore all the options, all in one place – only at Build It Live.

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What Are the Main Benefits of ICF Construction?

One of the biggest advantages of building with ICF is its exceptional thermal performance. The continuous insulation and integral thermal mass of ICF means you should require less energy for heating and cooling, leading to long-term savings on energy bills and excellent comfort levels.

“There’s a great choice of insulation materials available to manufacture the formwork components,” says Robin Miller, managing director at Beco Wallform. “ICF can reach U-values as low as 0.10 W/m²K and the performance of some systems is already achieving the energy standards proposed for 2050.”

ICF Construction – What is Insulated Concrete Formwork & is it Right for Your Self Build?

The Build It Education House features Nudura ICF walling, from ICF Supplies, for the basement and above-ground external walls. The shell of the 80m² basement, fully insulated and ready to fit-out internally, was completed for £78,800 (£985 per m²)

Because the concrete is cast on site, it’s possible to create a highly airtight, monolithic structure with ultra-low PSI values (a measure of heat loss along a metre of junction at a joint or cavity), minimising drafts and heat loss in your completed home. “Air permeability values of less than 1m³/hr/m² are achievable, delivering a consistently comfortable internal living environment,” says Elliot McKendrick, commercial director at ICF Bondmor.

It’s then a case of specifying efficient windows, doors and other products, and ensuring they’re correctly installed, for a high-performance home. “Excellent insulation and airtightness can be achieved without the need for additional tapes and barriers,” adds Richard Douglas, business development manager at BEWI.

ICF Construction – What is Insulated Concrete Formwork & is it Right for Your Self Build?

The construction of this home by ICF Bondmor used 484m² of ICF walling with a 412m² insulated raft foundation. The entire build took 60 days to complete, and the finished property has an impressive airtightness level of 0.26m3/hr/m²

The concrete core means ICF walls are ultra-strong, offering great durability and protection from extreme weather. “It provides outstanding safety, with fire ratings up to four hours,” says Lisa Trewin, owner and director at R-Wall Ltd. “Plus, the main structure is capable of withstanding winds of up to 250mph.” This makes ICF a popular choice for homes in exposed areas or those prone to natural hazards, such as earthquakes or flooding. The dense core also provides excellent soundproofing, making it well-suited to creating calm, enjoyable spaces.

It enables the use of concrete floor structures to provide open-plan spaces with reduced internal noise transfer.  “ICF is very low-maintenance,” says Richard. “Your structure won’t deteriorate over time from wear and tear.” This means you can create a longlasting, futureproof home with little upkeep, except to your exterior finish.

What’s more, ICF is a relatively straightforward system, offering an efficient build programme. “Speed of construction is another great benefit,” says Chris Oram, technical sales at ICF Supplies. “It’s possible to keep building work moving in the rain, so your project won’t necessarily be held up by bad weather.”

What Architectural Features Can Insulated Concrete Formwork Create?

ICF offers the flexibility to achieve a range of architectural styles and finishes. “If you can imagine it, you can build it with ICF,” says Chris. The system’s innate strength means you can incorporate wow-factor design features, from curved walls and arches to large cantilevers, big spans of glazing and expansive open-plan living spaces.

ICF Construction – What is Insulated Concrete Formwork & is it Right for Your Self Build?

Build It readers Ray and Ruth Davis engaged ICF builders Econekt for their part-subterranean home. ICF allowed ample glazing in the project’s design. The apex gable on the rear elevation has two sets of sliding doors installed above one another across two storeys, creating the feel of a fully glazed facade

“ICF blocks are engineered with regular mechanical fixing points which allow for the direct application of cladding or masonry ties,” says Elliot. So, whether you’re looking to create a heritage-style facade or an ultra-modern design, ICF supports a range of cladding materials, such as brick, timber and render. “It’s possible to create a highly customised look while keeping the energy-efficient core intact,” adds Anthony.

What Should You Consider When Building an ICF Home?

As with any system, building with ICF requires thoughtful planning and a coordinated approach. Here are some critical aspects to consider for an ICF project:

1. Site preparation & structural engineering

It’s essential to prepare your site effectively and ensure your design is tailored to support the concrete pours. “Your concrete will arrive in large wagons and be injected with boom pumps, which also require a lot of space,” says Elliot. The ground conditions on your site need to be assessed to ensure they can support the weight of the necessary equipment. “Working with engineers who understand ICF is crucial,” says Anthony. This will help to optimise the building’s structural performance and ensure your project runs smoothly from start to finish.

2. Construction sequencing

The timing of your concrete pours needs to be carefully planned and incorporated into your overall construction timeline. Map out each stage, so you know everything is in place and you can ensure an efficient build programme.

“It’s vital to avoid any alterations once your project has started,” says Robin. As with most systems, changes to your design may not be possible after your plans have been finalised and works started. Cutting concrete requires specialist equipment, so alterations are likely to lead to substantial added costs.

ICF Construction – What is Insulated Concrete Formwork & is it Right for Your Self Build?

Homeowners Derrick and Gail found the perfect self build opportunity at the top of their garden – a sloping plot that offered spectacular views of the Cotswolds. Supplied by Sandalcroft Construction, and awarded Best ICF Home, this ICF home embraces the site perfectly

3. Incorporating services

Plumbing and electrics need to be considered early on in the design and build process, as these systems are integrated into your ICF walls. Detailed planning will ensure these elements are incorporated smoothly and successfully into your structure. “Because it’s a dense material, ensure penetrations for your services are placed through the ICF prior to pour,” says Lisa. This will be more convenient on site and contribute to great levels of airtightness.

4. Wall thickness

ICF walls are generally thicker than many alternative methods of construction. However, finishes such as modern render can be direct-applied, saving time and helping to minimise wall depth. Internally, most self builders will switch to blockwork and stud walls rather than ICF to maximise the floor plan.

How much does it cost to build a house using ICF construction?

Building with ICF generally comes with a higher upfront cost than some alternative build systems. “Generally speaking, we’ve seen that ICF can cost approximately 10% more than other standard construction methods for one-off builds,” says Elliot.

However, this is typically offset by long-term savings on ongoing costs such as energy bills, ease of maintenance, and the excellent longevity of your completed home. “Self builders can expect to pay between £150-£190 per m² of wall for installation, labour, hire of props, rebar, concrete supply and placement,” says Anthony. “This is for above ground structures, depending on the complexity of the project, location and material specifications.”

ICF Construction – What is Insulated Concrete Formwork & is it Right for Your Self Build?

Jim and Lesley Driver replaced a poorly insulated coastal bungalow with a highly efficient ICF home, true to the area’s Bauhaus roots. Designed by LA Hally Architect and built using a highly-efficient system from ICF Homes, the 250m² project cost a total of £857,000. Photo: Simon Maxwell

“As building standards move progressively towards Passivhaus or equivalent levels of performance, ICF will become increasingly cost-effective as much of the requirements for reaching these values is already built into the system,” says Robin. The energy efficiency, comfort, flexibility and durability that come with an ICF home make it a wise long-term investment.

Why is it Important to Assemble the Right Team When Building a House with ICF?

Work with architects, engineers and builders who have experience with ICF to maximise your chances of a smooth and successful project that delivers on your specifications. “Collaboration between the principal design team and specialist contractors and consultants is always the best practice,” says Elliot. “This allows for value engineering of your scheme to find the most cost-effective solution.” More architects and trades are familiar with ICF these days, partly thanks to suppliers’ training, meaning it’s easier than ever to find good partners.

That said, if you want to get more hands-on with your project, ICF could be a good choice. “With a head for detail and basic DIY skills, carrying out the build yourself is very achievable,” says Chris. There are limits, however; basement projects should always be carried out by a professional, for instance, due to their added complexity. “If you’re considering a hands-on build, it’s important that your chosen supplier provides you with good training and a technical support programme,” says Robin.

ICF Construction – What is Insulated Concrete Formwork & is it Right for Your Self Build?

Designed by AV Architects with ICF Supplies, this stunning heritage-style self build in Kent features four storeys, eight bedrooms and has a high B energy rating

Whatever your level of involvement in the build itself, it’s vital to discuss your design with a trusted supplier early on to make sure the system will meet your unique requirements and project goals. Where possible, speak to people who live in or have built their own ICF homes and visit a live site to understand the benefits first hand. “Get as much independent feedback as you can, so that the supplier and design you specify is best suited to your site and preferences,” says Chris.

Insulated Concrete Formwork FAQs

Q) How are window openings formed when building with ICF?

This will depend on the exact system you choose. The Nudura method uses pre-formed EPS closers that slot into place at the top, bottom and sides to contain the pour (with timber bracing) and maintain the thermal envelope. Alternatives include inserting temporary metal frames. Whichever option you choose, the key is to triple-check everything’s as it should be before the pour, as cutting concrete back after the fact isn’t much fun.

Q) How is the roof of an ICF home constructed? 

ICF is a walling-only system. Most self builders will go for conventional Fink or attic trusses for the roof. You can switch to options such as SIPs (structural insulated panels) up top if you wish, but double-checking your engineer can deal with both elements first; otherwise you could be adding complication.

Q) How are internal walls of an ICF Build constructed?

You can use ICF, and it may make sense to for load-bearing internal walls or where you need great sound performance. But the downside is they will be pretty thick – hence to maximise floor space, many people switch to standard blockwork for load-bearing internal structures, and timber studs for partitions.

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