The sheer variety of underfloor heating setups and their scenario-specific additional components make them suitable for virtually any sub-floor structure and floor covering. We recommend using screed for both ground floor and higher storeys due to the benefit they bring to the renewable energy system.
Screed is a mix of sand and cement that’s used in buildings’ floor constructions, and it’s usually poured or spread over structural concrete or insulation, beneath the floor covering.
What’s the benefit to underfloor heating screed?
There are two main benefits to using screed:
- Cost: These sub-floor structures are the most economical because they avoid the sizeable costs of additional components, such as spreader or heater plates and floor panels. While these extras certainly add benefit to the underfloor heating system, the added cost would be better spent on a more closely-packed pipework design. This in turn allows us to further reduce the flow temperature even in rooms that lose heat easily, such as conservatories.
- Thermal battery principle: Screed has an inherently high thermal mass, which means it can hold a large quantity of heat. By having this ‘heat battery’, we can run the heat pump at peak air temperature / solar generation times. The underfloor heating system will effectively charge the heat battery, so that when the temperature outside falls in the evenings, the screed will gently release the heat long after the underfloor heating has been switched off, keeping your home warm throughout the night.
Underfloor heating screed
Liquid screed – either pumped anhydrite or flowing cement – is poured directly over the underfloor heating tubes, which are stapled onto rigid insulation boards (typically Kingspan or Celotex). The screed is then left to dry, forming a solid block with underfloor heating tubes inside. Once the screed has dried, the floor covering is laid on top.
This method of installing underfloor heating is also applicable on other storeys, providing they have block and beam or concrete structures. Using liquid screed ensures no insulating air bubbles can form between the tubes and the floor covering, which would otherwise prevent the movement of heat.
Wooden batons are fitted between the troughs of the joists to support rigid insulation boards. The joists are then notched to allow the tubes to pass across the joists without losing floor height. To ensure that the notched joists are structurally sound, we employ a structural engineer at this point. If this isn’t possible, we raise the level of the floor slightly, and lay the tubing over the top joist level.
After the pipes are secured to the insulation boards, the dry screed is laid (also called ‘Pug screed’ or biscuit mix), before adding the final floor covering.
What’s the best floor covering for underfloor heating?
Stone, tile and polished screed floor covers are naturally good conductors of heat, with little thermal resistance. If you’d like a wood finish, engineered timber boards are advised. This is because they don’t expand and contract due to changes in humidity and temperature like natural wooden flooring.
While underfloor heating can be used under carpets, we suggest that the combined tog rating of carpet and its underlay is no greater than 2.5 – any greater than this would trap the heat below the carpet.
What we do differently
Before any underfloor heating system install, we work closely with homeowners to ensure that your underfloor heating system will work effectively and efficiently with your chosen floor covering. We carefully consider the thermal resistance of these floor coverings, since this – along with the shape, size, and heat loss calculations of individual rooms – will ultimately dictate the layout, thickness and spacing of the pipes.
Our design team will provide consultancy support for floor coverings and structures suitable for both new builds and retrofits. All our proposals come with bespoke CAD drawings that are sympathetic to your design specifications. You can find out more about our process on our what we do page.