Maximising the benefits from below

Toby Howard-Willis of JG Speedfit offers some advice on how to achieve the full benefit of an insulated underfloor heating system

The self-builder market is increasingly looking towards underfloor heating (UHF) systems as a cost and energy efficient way to heat a building. However, the energy savings that UFH can deliver to a homeowner often fail to be maximised because the correct design protocols have not been followed.

Modern homes have a number of inherent heat loss areas built into their design, which can limit the effectiveness of UFH. One way of countering this is by considering the right type of insulation at the design stage.

UFH is becoming increasingly popular with the self-build market, for a number of reasons. It offers a more convenient alternative to traditional radiator heating systems. Not only is the system essentially invisible, since it works by tubing embedded in the floor, but it can also be cheaper to run and is often more energy efficient than radiators.

It works by pumping a controlled flow of warm water from any heat source such as a boiler or heat pump, through pipes installed underneath the floor. This also means that pipework is hidden, and there is no need to hang traditional radiators on the wall, which can take up considerable space in properties.


Insulation is an important consideration when installing UFH – we always recommend that self-builders install insulation with UFH systems. It ensures that as much heat as possible goes upwards into the house, limiting the amount of heat which travels down into the ground.

The general rule is that the more insulation you have, the smaller the amount of heat you are losing through the external fabric of a building. This also means that the heating demand on your UFH system is greatly reduced.


Multiple types of suitable insulation exist, falling into various categories. You can have polystyrene insulation, which is considered the more traditional type, or glass fibre insulation, a product commonly used in lofts.

Some builds will require glass fibre insulation. This is often used for joisted floors on the ground and for the first floor in older buildings where it is used with spreader plate systems.

A lot of self-builders also like to use an expanded foam insulation with a foil backing. This has particularly good heat retention properties.

Which of these materials will be more effective largely depends on the application and the type of building. However, it is almost a foregone conclusion that at least 95 per cent of new builds or extensions will use a foil- backed foam insulation.

Generally speaking, the way modern buildings are being constructed means they’re creating a demand for expanded foam insulation. For many years, self-builders and installers used very basic insulation which had to be extremely thick. Expanded foam has a significantly higher heat retention rate than many other forms of insulation. The advent of expanded foam has also greatly reduced properties’ heat loss.

Further considerations

Once you have selected your type of insulation, there are still further decisions that need consideration. For example, the position of insulation within the floor structure always needs to be considered. In 2002, changes were made to Building Regulations, stating that all new builds must have insulation below the concrete slab. All screeded floors will already have insulation below them, regardless of whether an UFH system is installed.

When it comes to the question of how much insulation to use, the answer is – really as much as possible. Regardless of whether or not UFH is installed, you can never have too much insulation under a floor.

Most properties will emit a fairly constant amount of heat due to windows and doors. Even the best quality double glazed unit will emit heat a lot more easily than a brick wall would. When you consider the current trend to have open plan rooms in modern buildings, and more glass and windows, insulation becomes even more important since the heat loss areas have been increased.

There are also various aspects to take into account when installing insulation in order to ensure you get it right first time. The type of building, floor construction, and height allowance of the floor will all help to dictate which type of insulation to use.

It’s always advisable to use an UFH manufacturer that offers a free of charge consultation and full design service prior to commencing any project. Some will further support this with aftersales technical support, should it ever be needed.

Toby Howard-Willis is technical sales manager at JG Speedfit