SUBFLOORS & SCREEDS
AS the construction industry continues to respond to tightening building regulations, rising energy costs and increasing pressure to reduce carbon, attention is turning to parts of the building fabric that can quietly deliver significant performance gains. One such area is the subfloor build-up, specifically, the relationship between screed choice and underfloor heating (UFH) or air source heat pump (ASHP) systems.
When designed correctly, the screed layer plays a critical role in both the thermal efficiency and long-term performance of a floor. In recent years, flowing screeds have increasingly been specified alongside UFH and ASHP systems due to their ability to enhance heat transfer, reduce material use and improve installation efficiency.
Thinner screeds, better heat transfer
A key advantage of flowing screeds is their reduced installation thickness. When used with UFH systems, flowing screeds are typically installed at an overall depth of around 40mm, providing about 20mm of cover above the heating pipes. In contrast, traditional sand and cement screeds, as well as many self-compacting concretes, are generally laid at a minimum thickness of 75mm, equating to around 55mm of cover.
This difference in depth has a direct impact on thermal performance. Flowing screeds fully encapsulate the heating pipes, eliminating voids and ensuring consistent contact between the pipework and the surrounding material. Heat is transferred more evenly and more efficiently into the floor surface, reducing warm-up times and improving system responsiveness.
With less screed material to heat, UFH systems can operate more effectively, particularly when paired with low-temperature heat sources such as air source heat pumps.
Supporting U-value compliance
The ability to install screeds at a reduced thickness also brings benefits at a whole-floor level. Achieving low U-values, such as 0.11 W/m2K, becomes more straightforward when screed depth can be reduced in favour of increased insulation thickness within the same floor build-up.
This flexibility is increasingly valuable on projects where floor zone depths are constrained, floors are retrofitted, or where designers are seeking to maximise thermal performance without increasing overall floor height. By optimising the balance between insulation and screed, flowing screed systems support compliance with current regulations while helping future-proof buildings against further tightening of standards.
Lower running temperatures, lower energy demand
Studies have shown that UFH systems installed with flowing screeds can achieve the same room temperatures while operating at thermostat settings up to 5°C lower than those using thicker traditional screeds. This reduced operating temperature is particularly beneficial for ASHP systems, which deliver their highest efficiencies at lower flow temperatures.
The result is a floor heating system that responds faster, consumes less energy and delivers more consistent comfort, without compromising structural performance.
At the same time, improved heat transfer and reduced operating temperatures contribute to ongoing operational carbon savings throughout the life of the building. When viewed together, these benefits make flowing screeds an increasingly attractive option for projects targeting lower whole-life carbon impacts.
A smarter foundation
As flooring systems continue to evolve, the role of the subfloor should not be overlooked. By improving thermal performance, supporting regulatory compliance, reducing carbon impact and accelerating installation, flowing screeds offer a smarter, more efficient foundation for modern buildings, proving that performance gains often start from the ground up.
www.flowingscreedsassociation.com
Ben Bland is director Flowing Screeds Association