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Underfloor Heating Insulation

There are several factors which affect the performance, and therefore the efficiency, of an underfloor heating system. The type of system used will have an impact on the amount of energy required to heat the property, while the type of flooring will also have a bearing on running costs and energy efficiency.

The size of the rooms or zones to be heated, the overall energy performance of the house, and the use of a renewable energy source to heat the underfloor system, all play a part in determining how well the heating performs.

For effective underfloor heating you require insulation to be fitted.

Insulation is important for efficient underfloor heating.

Insulation is one of the key factors to consider when fitting an underfloor system, to ensure best performance and efficiency. Building regulations state that floors in new buildings should have a U-value of 0.25w/m2K.

This is a measure of how much heat is lost to the ground, the lower the figure the more efficient the building. When underfloor heating is installed into a new build, the regulations stipulate that the U-value should be 0.15w/m2K.

By minimising the amount of heat lost to the ground and into the walls of the building, you will achieve the optimum performance from your heating system; reducing running costs and lowering your carbon emissions.


Why do you need insulation when installing underfloor heating?

An underfloor heating system can only produce a certain amount of heat. Indoor rooms are able to supply up to 100 watts per square metre at a maximum, and the system will only be able to heat to the maximum temperature that the floor finish can cope with.

It is essential then, to have a well insulated property to help retain the heat as much as possible.

Insulation board laid beneath the heating system stops heat escaping to the ground, and reflects heat back up into the floor, helping it to heat quicker.

Edge insulation is also laid around the perimeter of the system once it is installed to stop heat transferring into the walls or doors of the building.

Good loft insulation will reduce the amount of heat loss through the roof, and double glazing reduces the amount of heat lost through windows.

Installing these different types of insulation will mean that your underfloor heating is able to heat the house comfortably, and is not set at a higher temperature or used more often than necessary.

Without good insulation underneath it, or in a house which suffers heavily from heat loss due to poor insulation, underfloor heating may struggle to heat a room at all.


Is insulation required for both wet and electric systems?

Insulation is required for all types of heating system, including wet and electric underfloor heating. There are some differences in the types that can be used with each system, although some insulation can be used with both.

Insulation board is laid in a new building as part of the installation, but if you are working on a refurbishment project you will have to consider how the insulation is going to be fitted. If it involves too much work excavating the floor to install the system, then perhaps it is not the ideal system for that particular property.


The different types of insulation required when installing underfloor heating

Insulation board

Thermal insulation boards are fitted underneath the heating system to avoid any heat losses into the ground; some are designed specifically for use over concrete subfloors or cement screeds, while others are made for use with timber floors.

To avoid heat loss into the ground underfloor systems require thermal insulation boards.

Fitting thermal insulation beneath underfloor heating.

Fastwarm is one prominent manufacturer of insulation boards, and they offer a range of insulation which is derived from extruded polystyrene foam. It is fully recyclable and the manufacturing process is completed with a zero ODP (Ozone Depletion Potential).

The insulation board for use with concrete subfloors or cement screeds has a compressive strength of thirty tonnes per square metre, and is available in depths of 6-60mm.

The boards can be cut to shape quickly and easily with a knife to speed up installation, and incorporate a specially prepared surface designed for use with water based tile adhesives, which will create a bond without any need for extra priming.

For use with timber floors they offer a similar product, made from extruded polystyrene core. It is covered with a glass fibre mesh coating, which is reinforced by a polymer cement layer to improve stiffness and prevent flexing.

These insulation boards are entirely water proof, and will not rot. Available in thicknesses of 6-10mm, the boards are ideal for use with wooden and timber floors, and have the same pre-prepared surface to form a strong bond with tile adhesive when fitted.

Edge insulation

It is necessary to fit edge insulation as part of an underfloor system, as it reduces heat loss into walls and doors of the property. The edging should be fitted around the perimeter of each room and around any fixed structures such as stairs or columns.

It also has another important role to play as part of the overall heating system, as it acts as an expansion gap for the screed and the flooring.

They will expand and contract as the system heats and cools, and the edge insulation prevents the screed from crossing the divide between the edge of the wall and the floor insulation.

It can be bought in a roll and is usually around 8mm thick. This edging should not be forgotten as it is integral to the best performance of your system.



Any heating system requires good insulation to work effectively; underfloor heating perhaps more so than other types as there are limits on the temperatures it is able to run at.

A property benefitting from good loft insulation and double glazing will retain heat much better, thus reducing the demand on the heating system to maintain a comfortable temperature.

If an underfloor heating system is fitted, it is essential to install the right type of insulation board for the type of subfloor in the building to reduce heat loss to ground; while edge insulation must be fitted around the perimeter of the system.

With these measure in place you are more likely to achieve the optimum performance from your system, and ultimately save more money.

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