The increasing use of wood as a flooring material in the UK over the last decade, in both the commercial and domestic sectors, has brought with it a number of developments which have made use of its versatility as a construction material. Nowhere is the versatility of this substrate more self-evident than in its use as a floor covering for underfloor heating systems.
To increase their market share in what is perceived as a buoyant commercial sector, wood flooring manufacturers have developed systems designed to be used directly over heated sub-floors. This is in response to growing demands for a healthier and more comfortable living environment, in both the home and the workplace.
Underfloor heating is recognised as a more energy-efficient means of heating, in that the entire floor area is used as the source of radiant energy. Given the larger surface area involved, underfloor heating systems operate at much lower surface temperatures than conventional radiators and therefore air movements induced by convection currents or thermal updraughts are kept to an absolute minimum. In essence, this means that the floor is heated from the bottom up and minimises energy dissipation at the level of the upper walls and ceiling.
In order to maintain a stable room temperature of 20-21°C, an underfloor heating system should operate at around 26-27°C, as compared with 75-80°C for a conventional radiator. Operating at lower working temperatures brings with it an advantage in that materials which at higher temperatures would exhibit excessive movement and distortion, can be used as floor coverings.
Laying a screed floor to be covered with wooden flooring
Wood is just such a material. It is hygroscopic and therefore thermally responsive in that its moisture content can change with temperature. This, in turn, can induce dimensional movement. By using hardwoods which exhibit very low thermal movement and by limiting their width to no greater than 75mm, such problems can be averted as long as the installation is carried out with the boards at a moisture content of between 6% and 8%. This may sound complex, but to enjoy the considerable benefits wood flooring combined with underfloor heating can bring, it’s important to follow these guidelines to ensure stability.
Contrary to expectation, underfloor heating systems actually work to maintain a more stable climatic environment, minimising the fluctuations in relative humidity which can cause wood to move. This again is due to the low temperatures needed to operate the heating system which minimise the generation of a “heat stack” – the effect where rising warm air draws in colder and humid air into the building through cracks and voids in its fabric. The absence of a heat stack leads to a far more stable microclimate than that created by the higher temperatures of conventional radiators.
The choice of species used for underfloor heating can be significantly extended by choosing engineered boards where a wear-layer and backing veneer are cross-banded to a central softwood core, making a product which is very dimensionally stable. This has environmental merit in that it uses short off-cuts of otherwise waste material in a way which produces an attractive, cheaper and stable alternative to solid wood flooring and alleviates pressures of supply on hardwoods from recognised sources.
Wood flooring has traditionally been considered as a healthier alternative to carpets and other textile floorcoverings, particularly for asthma sufferers, in that it provides less opportunity for house dust mites to breed. This advantage is further augmented if the floor is used in conjunction with underfloor heating, since the minimal air currents generated contribute to a reduction in the airborne circulation of dust mites and other allergens.
Two heating methods are available: electric systems or water pipes directly embedded into the screed. Both systems can be used equally well with wood floor coverings, although the electric method provides a direct source of heating, while water pipes require a large initial energy input to heat the surrounding screed, adding to energy demand.
Once heated, the system acts rather like a storage heater and can re-radiate energy after the heat source has been turned off. One problem associated with this type of system is that its responsiveness is reduced. This may mean that the heating has to be on longer to achieve a stable temperature.
Wood floors offer a way around this problem in that, by fixing battens onto the cement base and filling the spaces between the battens with insulation, the pipework can be housed within the insulant, thereby converting the water system into a direct heat source.
Other means of heat distribution in the form of heat exchangers placed beneath the pipes and between the supporting battens can reduce the phenomenon of hot-spots on the floor surface created by an inconsistent
distribution of pipes – particularly at junction points – to maximise heating efficiency.
Wood floor coverings over underfloor heating systems can therefore reduce the incidence of in-service problems and aid thermal distribution and energy efficiency. In so doing, they offer a fully functional and visually attractive flooring option that can contribute to a comfortable and healthy environment with truly universal aesthetic appeal.
Keywords: Flooring underfloor heating
