Electric underfloor heating advice
Do I Need Insulation Under Electric Underfloor Heating?
Not in every installation—but we recommend it for most projects.
A suitable insulation layer can reduce downward heat loss and help the floor warm more quickly. The right build-up depends on the existing floor, the space below and the final floor finish.
The short answer
Insulation at a Glance
Insulation is not compulsory beneath every electric underfloor heating system, but we recommend it for most installations. The best answer depends on the floor construction, the space beneath it, the floor finish and the selected heating system.
| Floor or installation | General recommendation |
|---|---|
| Uninsulated concrete or ground floor | Strongly recommended |
| Floor above a garage, cellar or unheated void | Strongly recommended |
| Modern, well-insulated ground floor | May be optional |
| Upper floor above a heated room | Usually less critical |
| Timber floor | Use an approved board or build-up |
| Wood, laminate, carpet or vinyl finish | Follow the complete system build-up |
| New build, extension or major renovation | Check applicable Building Regulations |
Floor above a garage, cellar or unheated void
Strongly recommendedModern, well-insulated ground floor
May be optionalUpper floor above a heated room
Usually less criticalTimber floor
Use an approved board or build-upWood, laminate, carpet or vinyl finish
Follow the complete system build-upNew build, extension or major renovation
Check applicable Building RegulationsUnderstand the build-up
Floor Insulation and Overlay Boards Are Not the Same
Both may be described as insulation, but they perform different roles and should not be treated as interchangeable.
Structural floor insulation
Installed within the floor construction, such as beneath a slab or screed or between floor joists. It controls heat loss through the building fabric and helps the floor achieve its required thermal performance.
Overlay insulation boards
Thinner boards installed directly beneath a mat or cable. They can provide a thermal break and compatible installation surface, but do not replace structural insulation required within a new floor.
Why insulation helps
What Are the Benefits of Installing Insulation?
A suitable insulation layer helps more of the available heat move towards the floor finish and occupied room.
Faster warm-up
Reducing heat absorbed by a dense subfloor helps more warmth reach the floor finish sooner.
Reduced downward heat loss
More of the available heat is directed towards the occupied room instead of the ground, void or unheated space below.
Improved responsiveness
A more responsive floor can reach its target sooner and follow thermostat schedules more effectively.
Compatible installation surface
Some rigid boards also provide a suitable surface for the heating and floor finish when installed over a stable, prepared base.
Where it matters most
When Is Insulation Most Important?
Suitable insulation is particularly valuable where the construction beneath the heating can absorb or lose a significant amount of heat.
Over an older or uninsulated concrete floor
On a ground-floor installation
Above a garage, cellar, passage or ventilated void
In a conservatory or another higher-heat-loss room
Where rapid warm-up is important
Where electric UFH will be the room's primary heat source
Existing insulated floors
When Might an Overlay Board Be Optional?
An additional overlay board may provide a smaller benefit where the floor already contains effective structural insulation or the room below is also heated.
Even then, a thin compatible layer may improve warm-up time. The complete build-up must still suit the heating system, floor finish and available floor height.
Match the substrate and finish
Which Insulation Should I Use?
The correct material and fixing method depend on the existing floor, the electric heating system and the final floor finish.
Concrete or screed beneath tiles
A compatible rigid insulation or tile-backer board can be installed over a properly prepared concrete or screed base. The base should be sound, level and free from contamination. Bond and fix the board by the method specified by its manufacturer.
Timber floor beneath tiles
The timber floor must be securely fixed, stable and sufficiently rigid. Use a board and fixing method approved for timber; do not use the board to conceal loose boards, movement or structural deflection.
Wood or laminate flooring
Use the specific insulating underlay and any vapour or protective layer stated in the heating-system instructions. A general-purpose soft underlay can insulate above the heating and restrict useful heat transfer. Keep the combined thermal resistance within the flooring manufacturer's limit.
Carpet or vinyl flooring
These finishes normally require the heating to be enclosed within a stable, load-spreading construction. Do not place carpet, vinyl or a soft insulation layer directly over a cable unless the complete system is designed and approved for it.
In-screed heating cables
The principal insulation is normally incorporated beneath the heated screed or slab. Its thickness and thermal performance should be established through the building's floor design rather than selected only from the cable requirements.
Plan the whole floor
How Thick Should the Insulation Be?
There is no single correct thickness. Thicker insulation of the same material normally provides greater thermal resistance, but thickness alone does not compare different products.
- 1Whether structural insulation is already present
- 2The floor's required thermal performance
- 3The material's declared insulation value
- 4Available floor-build-up height
- 5Door and threshold levels
- 6The room or space beneath the floor
- 7Substrate stability
- 8Heating-system instructions
- 9Final floor-finish requirements
Project-specific requirements
Do Building Regulations Apply?
Building Regulations may set thermal-performance requirements for new floors, replacement floors, extensions and certain renovations. The applicable standard depends on the UK nation, project type, building construction, scope of work and any transitional arrangements.
Ask the architect, energy assessor, insulation manufacturer or relevant building control body to confirm the required floor U-value and insulation specification for the project.
Installing without a board
Can Electric Underfloor Heating Be Installed Without Insulation?
Some electric systems can be installed directly onto a suitable concrete, screed or prepared timber substrate. That does not necessarily make omission the best choice: the floor may take longer to warm and more heat may be absorbed by the structure below.
Electric underfloor heating advice
Frequently Asked Questions
Clear answers about insulation thickness, upper floors, floorboards, warm-up time and running costs.
Is insulation compulsory with electric underfloor heating?
Not in every installation. Some systems can be fitted directly onto an appropriate substrate. Insulation is nevertheless recommended where it can reduce downward heat loss and improve warm-up time.
Will insulation reduce running costs?
It can reduce avoidable heat loss beneath the heating system. The actual effect on running costs still depends on the room, floor construction, thermostat settings, heating schedule and energy tariff.
Is a 6mm insulation board enough?
A thin board can provide a useful thermal break and improve response, but it is not equivalent to the structural insulation used within a compliant new floor. Select the board according to the complete build-up rather than thickness alone.
Do I need insulation on an upper floor?
The benefit is usually smaller when the room below is also heated. A compatible insulation layer may still improve response and help direct more heat into the intended room.
Can I install insulation board over floorboards?
Only when the floorboards are secure, stable and suitable for the proposed board and floor finish. Use the required mechanical fixings, adhesive and joint treatment stated by the manufacturers.
Should the insulation go above or below the heating?
Insulation is generally positioned beneath the heating element so that it does not restrict heat transfer into the room. Always follow the exact layer order shown in the heating-system instructions.