ICF is one means available for reducing the carbon footprint of new housing, says Christopher Stride of the Insulating Concrete Formwork Association.
The drive to improve levels of energy efficiency and airtightness while reducing a building’s reliance on heating and cooling systems has paved the way for Modern Methods of Construction (MMC) to provide simple solutions.
Taking a fabric-first approach is considered the most effective approach to achieving these standards with the concept featuring heavily in the Part L changes which are an interim step to the Future Homes Standard. This focuses on enhancing the building’s.
Although many think MMC means volumetric builds, it is in fact an umbrella term which encompasses a vast array of systems. Each one is different, but they all provide the speed while creating high-quality, energy-efficient homes.
Site-based insulated solid wall construction methods like ICF sit under the MMC umbrella. A system that uses construction methods already familiar to contractors enabling it to integrate easily into developments.
When used correctly, ICF offers excellent buildability, flexibility, and virtually limitless design potential. A great example of this is the ease of adding aesthetic details, such as recessed doors and windows. In fact, some design elements, like corner windows or cantilevered openings, are simpler to construct with ICF compared to traditional methods because they don’t require complex structural solutions.
It’s not just about U!
ICF systems provide high levels of energy efficiency. One of the biggest problems in achieving high U-value levels is ensuring the installation of the insulation is correct – any gaps and the building will underperform. This is not typically a problem with ICF. During construction, the blocks lock to keep the concrete in place while setting.
The combination of the tight fitting insulation, which wraps both sides of the building, sitting in direct contact with the concrete provides one of the biggest benefits of ICF structures. While figures can vary depending on the chosen system and building design, ICF constructions typically achieve U-values around 0.18 W/m²K.
Of course, creating energy-efficient buildings is not only about the level of insulation used. Solid concrete wall construction also ensures good levels of airtightness – as low as 0.3 m³/hr.m² and superior thermal bridging performance with Y-values as 0.02 regularly being demonstrated using certified junction psi values. This is a critical factor in their outstanding thermal performance, achieved when combined with their inherent air tightness and low U-values. This results in even temperatures throughout the structure with reduced draughts and cold spots enabling the building to stay warm in the winter and cool throughout the summer.
Energy efficiency in practice
A great example of ICF’s potential is The Curly House by Nudura. The client’s brief was to rebuild an existing cottage to Passivhaus standards to minimise their energy consumption and carbon footprint while also meeting planning restrictions faced when building in an Area of Outstanding Natural Beauty. The energy efficiency challenge was even greater when working on a highly exposed site subjected to bitingly cold winters and very hot summers. The design by architects Ecotecture consists of a crescent-shaped detached home which steps and slides into the slopes of the site and features a curved brise soleil.
Nudura was specified for the walls with a thermally broken super-insulated deck system that would take a load of 5 kN/m. The heavier construction option was chosen to provide thermal mass that balances the heating gains and losses due to the large areas of glazing. The insulating element of Nudura’s ICF acts as a buffer to the thermal mass allowing the slow release of heat into the building to ensure a constant internal temperature throughout the year. The semi-subterranean nature of the design also meant that the build materials had to withstand a damp environment – ruling out the option of timber.
The finished design and ICF have made it possible to reduce thermal bridging to a minimum with the enhanced air-tightness standards required for Passivhaus compliance.
Christopher Stride is chairman at Insulating Concrete Formwork Association