Renovation
Underfloor heating in a renovation, with no screed and no channels to cut.
In renovation, three answers keep coming up: cutting channels into the screed, laying a thin water-based system, or a dry system. All of them need water, a manifold and a heat generator. The fourth is electric and is 5 mm thick.
The short answer
Yes, underfloor heating can be added without pouring a screed and without cutting channels into the one that is there. The system is 5 mm thick: a reflective layer, an insulating layer, a carbon film. It is laid on the floor already in place, and the new floor covering goes on top. No pipes, no drying time.
The height, floor covering included
This is the figure that counts in renovation: it decides what happens to the doors, the thresholds and the skirting boards. Indicative values from the manufacturer, 5 mm of heating included.
| Floor covering | Build-up | Height added |
|---|---|---|
| Click vinyl, floating | vinyl from 8 mm | 13 to 16 mm |
| Laminate, floating | laminate from 10 mm | 15 to 19 mm |
| Three-layer engineered wood, floating | the most common case | 16 to 20 mm |
| Glued-down wood flooring | on a decoupling mat | 19 to 25 mm |
| Tiles | on a decoupling mat | 23 to 38 mm |
| Thin vinyl or glued floor covering | on a dry screed of 18 to 23 mm | 27 to 35 mm |
| Tiles | on a dry screed | 35 to 40 mm |
| Solid wood flooring, large planks | on a dry screed | 35 to 45 mm |
| Epoxy resin, decorative screed | on a 25 mm fibre-reinforced cement screed, with its manufacturer’s agreement and a heating-up protocol | 38 to 50 mm |
The last row is the only one where a screed is poured, a thin one, for a resin floor: it falls outside the general case of this page.
For comparison, the manufacturer gives 15 to 30 mm for a thin water-based system, without insulation or floor covering, and 45 to 65 mm for water-based underfloor heating cast in a screed.
The details by floor covering: wood flooring, vinyl and laminate, tiles.
The weight
| System | Weight, without the floor covering | For the structure |
|---|---|---|
| Carbon underfloor heating | about 1.25 kg/m² | no effect |
| Thin water-based system, with levelling compound | 15 to 35 kg/m² | to be checked |
| Water-based underfloor heating in a 45 to 65 mm screed | 90 to 130 kg/m² | structural assessment |
The manufacturer’s figures. On a timber floor, in a loft or on an added storey, this is often the deciding factor: the page added storey, loft, extension covers this case.
What is needed in your home
- A dry, sound and flat floor: a deviation of 2 mm at most over one metre. Beyond that, a levelling compound first.
- Electricity, no plant room: 230 V, with no transformer, no manifold, no outdoor unit. The electrician checks the circuit protection for each room.
- A water heater if the old heating also produced the hot water.
How the job goes
- Check of the existing floor.
- The reflective layer is rolled out, silver side up; then the insulating layer.
- The strips of film are laid side by side; the electrician connects them, room by room, through a thermostat.
- The floor covering is laid straight away.
- Check with the thermal camera, then handover.
The course of a day, hour by hour, is on the home page. The steps, from design to handover, are on the page fitting, step by step.
Where 5 mm is not enough
- An uneven floor needs a levelling compound.
- Tiles always need a mat or a dry screed: 23 to 40 mm.
- Glued-down wood flooring needs a decoupling mat: 19 to 25 mm. Solid or in large planks, it needs a dry screed: 35 to 45 mm.
- The shower itself and the space under fixed furniture stay without film.
To find out which build-up suits your home, send photos of the floor, the clearances under the doors and the floor covering you want: describe your project.
Frequently asked questions
Your questions on this subject.
Does the old floor covering have to be removed?
Most often, no. Tiles, screed, floorboards or vinyl stay in place if the floor is dry, sound and flat to within 2 mm over one metre. A floor covering that has come loose or is damp is removed or made good first.
Can it be laid on a timber floor?
Yes. At 1.25 kg per square metre, according to the manufacturer, the weight is no burden on the structure. The floor must be sound and flat.
Will the doors have to be trimmed?
It depends on the height added: 13 to 16 mm with click vinyl, 16 to 20 mm with floating wood flooring. If an old floor covering is removed, the manufacturer states that the doors generally do not have to be trimmed. We check this at the survey.
How long does the fitting take?
According to the manufacturer, one to two rooms a day, floor covering included; an apartment of around a hundred square metres was fitted out in one working day. No channels to cut, no screed to leave to dry.
Can we stay at home during the work?
Yes: we proceed room by room, with no dust from cutting channels and no wet screed. The other rooms remain habitable.
My home is poorly insulated. Is that an obstacle?
Insulation is not a condition for fitting. It weighs on consumption, as with any heating: the manufacturer has measured 23 to 64 kWh per m² per year in old, uninsulated buildings.
Read next
- The carbon systemA 0.45 mm carbon film that heats across its whole surface, under your floor covering. Build-up, outputs, temperatures and limits, according to the manufacturer.
- Under wood flooringA 5 mm carbon film under floating wood flooring: 16 to 20 mm in all, no screed, no glue. Which wood flooring is suitable, at what temperature, and what is not done.
- Under tilesUnder tiles, the carbon film needs a decoupling mat or a dry screed: 23 to 40 mm in all. Bathroom, shower, old tiles.
- Under vinyl or laminateUnder click vinyl of at least 8 mm: 13 to 16 mm in all, with no screed and no glue. Under laminate: 15 to 19 mm. The conditions, the temperatures, the limits.
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