Building with Insulated Concrete Formwork (ICF)
At ARCO₂ we are often asked about different construction systems and how they compare. One option that has become increasingly popular with self-builders and contractors is Insulated Concrete Formwork (ICF). We’ve now used ICF across many projects in Cornwall and beyond, and our sister company ADD Sustainable Construction is delivering multiple ICF homes on site today. Here, we share some of the benefits, challenges, and lessons learned.
Why Choose ICF?
ICF can offer a number of compelling advantages when compared with more traditional methods of construction:
- Thermal performance – With careful detailing, ICF provides continuous insulation under the slab, seamlessly connecting to the wall insulation. This ensures a thermal bridge-free design at the critical floor/wall junction. If the slab and wall core are joined, airtightness also improves significantly.
- Speed and resilience – Unlike timber or blockwork, ICF can be built in virtually all weather conditions. Construction is relatively quick, and we’ve found that heavy rain does not interrupt progress — a huge advantage in the Cornish climate.
- Robustness – ICF structures are extremely durable and are expected to last well over 100 years. Their resilience makes them particularly suitable for exposed coastal locations.
- Ease of use – First-fix services can be chased directly into the internal walls, eliminating the need for specialist service zones. We have also found that inexperienced self-builders can get to grips with ICF quickly, often surprising themselves with how manageable it is.
What are the Challenges?
The main drawback is the embodied carbon associated with the use of concrete. While “greener” concretes are now being developed, and could transform the sustainability profile of ICF, this remains the most important consideration when comparing it with timber frame.
Architects also need to understand the system’s limitations and opportunities. For example, ICF is excellent for eliminating steel lintels (these can be formed with ICF and rebar), cantilevers are possible, and depending on the system, curves can be achieved either on-site or prefabricated in the factory.
Do you need an ICF-experienced architect?
Although not essential, it is definitely beneficial. Most ICF suppliers provide design manuals and offer tuition to architects, contractors, or self-builders. That said, having a design team already familiar with the system can save time and ensure the design takes full advantage of its flexibility.
Are there forms or shapes to avoid?
We haven’t encountered any significant limitations yet — apart from very tight curves, which can be more challenging. Otherwise, ICF is surprisingly versatile.
How long does ICF construction take?
Timescales depend on the size and complexity of the project, as well as the system chosen. Pour heights vary, which can influence the programme, but overall ICF tends to be faster than blockwork or insulated timber frame. Importantly, progress is not halted by rain — a major benefit for winter builds in the South West.
Would we recommend ICF?
We always assess construction systems based on the site, design concept, and client priorities. Timber frame usually performs better in embodied carbon terms, but ICF has strengths that are hard to ignore:
- Lightweight, waterproof (depending on the system) and adaptable
- Quick to install and robust
- Can be left exposed for long periods without damage — ideal for self-builders working at their own pace
We often recommend a hybrid approach, combining the best of different systems depending on the demands of the project.
Case study: Ladybird Farm
At Ladybird Farm, we selected R-Wall as the ICF system. R-Wall are a Cornish company using XPS insulation, which is waterproof, adaptable, and helps to reduce waste. The project went on to win the Best ICF Home at the 2024 Build It Awards.
As a practice, ARCO₂ have now designed 12 R-Wall projects to date, making us one of the most experienced architectural firms in the South West when it comes to ICF. Our sister company, ADD Sustainable Construction, is currently building four R-Wall properties, alongside other projects using alternative ICF systems such as Nudura. This combined expertise allows us to support both clients and contractors with confidence, from concept through to delivery.
We have also seen first-hand how quickly contractors can adapt to ICF. For example, Perring Properties had not previously worked with ICF before Ladybird Farm, but quickly became experts. They are now advocates of the system, describing it as “too easy” compared to traditional methods. They are already building their second ICF project with us — this time a highly complex home with curved walls, a double-curved roof, and a basement.
Meanwhile, Westhaven Construction, with whom we regularly collaborate, are now on their 16th R-Wall build and preparing to construct another curved ARCO₂ design — testament to the system’s adaptability and our shared confidence in its performance
https://www.arco2.co.uk/sustainable-architecture-projects/ladybird-farm-2/
Manufacturing and durability
Unlike timber frame, which can be manufactured in a factory or stick-built on site, ICF is always constructed on site. Its major advantage is that it is unaffected by rain. Timber, if enclosed while wet, can suffer from moisture damage — a growing concern as Cornwall experiences higher rainfall and stronger winds.
For self-builders, who may take longer than main contractors, ICF can be more forgiving and resilient. We continue to champion timber frame where appropriate, but ICF offers a durable, versatile alternative — particularly where construction speed, robustness, or weather resistance are critical.
In fact, on many projects we now use a hybrid of systems, making the most of each method’s strengths. With ICF, the reduced number of layers also accelerates construction: airtightness is mostly achieved through the concrete core (removing the need for internal membranes or boards), service zones are unnecessary, and external render can be applied directly to the insulation. Fewer processes mean faster progress.
In Summary
ICF is not a one-size-fits-all solution, but in the right circumstances it can deliver exceptional results. At ARCO₂ and ADD Sustainable Construction, we have become recognised experts in designing and delivering ICF homes across Cornwall and beyond. Whether through R-Wall, Nudura, or hybrid systems, our focus is always the same — to create robust, sustainable, site-responsive buildings that perform beautifully for generations to come.
