Installing floors and tiling over underfloor heating

Underfloor heating in screeds

Underfloor heating systems are normally installed within the screed especially in new builds. It is recommended that the underfloor heating is installed as per the instructions of the heating manufacturer. However the general method is to secure the pipes or cables in position and then cover with a floating screed at a minimum thickness of 65 mm in domestic locations and 75 mm in commercial areas (unless specified differently by the heating manufacturer). All movement joints such as in stairways must be incorporated and followed through to the floor covering.

Once the screed is dry the underfloor heating should be commissioned. Cementitious screeds should not be forced dried as it may cause the screed to crack and curl. A standard sand and cement screed dries at approx. 1 mm per day (up to the first 50 mm). Regardless of the thickness the heating should not be commissioned for at least 21 days after the installation of cement screeds, or 7 days for anhydrite screeds. There are however, fast drying cement binders available which allow screeds to dry much quicker (click here for more information).

Underfloor heating commissioning

When the screed is dry then the commissioning can commence. It is recommended to follow the guidelines from the underfloor heating manufactures. However, the general rule of practice is to start from a low flow temperature of approx. 25°C and then gradually increase the temperature by approx. 5°C per day up to a maximum of 50°C and maintain for 3 days. The heating should then be switched off and allowed to cool, but not below 15 °C, before installing the tiles or floor covering.

Retrospective underfloor heating installation

Pre-fabricated UFH panels or matting

It is not always possible to install underfloor heating within the screed especially in renovation work where existing screeds have been installed already. Both electric and water underfloor heating systems can be installed retrospectively as part of renovation projects. It is recommended that these systems are installed as per the instructions of the underfloor heating manufacturer. These systems normally consist of matting or boards which contain the wires or pipes which are then installed over an insulation layer. Depending on the final floor covering a self-smoothing compound/screed, dry-board or tile adhesive can then be applied over the underfloor heating matting or boards before the floor covering is installed.

Screed boards (cement/calcium)

Installation of the boards should be in accordance with the manufacturers own specifications and no movement between joints.

Common manufacturer’s: Cellecta, Fermacell, Knauf

UZIN domestic installation recommendation

Primer: UZIN PE 360. Smoothing Compound: UZIN NC 196. Depth. 10 mm cover from the top of the pipework.*

UZIN industrial Installation recommendation

Primer: UZIN PE 360. Renovation Fleece: UZIN RR 201. Smoothing Compound: UZIN NC 770. Depth. 10 mm cover from the top of the pipework.*

Underfloor heating over High Density Foam Boards

High Density Foam Boards (HDF)

The installation of the boards should be accordance with the manufacturer’s own specifications.

UZIN recommendation

Primer: UZIN PE 630. Renovation fleece: UZIN RR 201. Smoothing Compound: UZIN NC 196. Depth: 10 mm cover from the top of the pipework.*

Important notes

Some HDF boards have foil tops whilst others are unfinished. Some unfinished HDF boards may have a webbing installed on them, in this instance no primer is required and the smoothing compound can be installed as an un-bonded application to the recommended depth.

Electric Matt

Installation of the electric matt system must be in accordance with the manufacturer’s specifications.

UZIN recommendation over dry screed boards (cement/calcium)

Primer: UZIN PE 360. Smoothing Compound: UZIN NC 196 for cementitious boards or UZIN NC 110 or UZIN NC 105 for calcium boards. Depth: 10 mm cover from the top of the cables.*

Important Notes

If the electrical heating matt has been installed prior to the installation of a suitable primer, then apply UZIN PE 260 primer over the entire system before the installation of the applicable smoothing compound.

electric under floor heating matt system

Crate system

Installation of the panels should be in accordance with the manufacturer’s own specifications.

UZIN domestic installation recommendation

Primer: Un-bonded. Smoothing Compound: UZIN NC 196, can be applied in multiple applications. Prime intermittent layers with UZIN PE 360. Depth: Minimum 10 mm cover above the pipework for resilient and textile floor coverings.* Timber and ceramic flush with the tray.

UZIN industrial installation recommendation

Primer: Un-bonded. Smoothing Compound: UZIN NC 770. Depth. Minimum 30 mm incorporating a 10 mm cover over the surface of the pipework.*

Important Notes.

Different manufacturer’s systems may vary in depth, however there is usually a standard depth of 20 mm from the base to the top of the crate system. This depth of crate would allow for a 10 mm minimum cover over the top of the pipework. However, if the system has a depth of less or more than 20 mm the application of the smoothing compound must remain at a minimum depth of 10 mm above the pipes.*

If the subfloor contains moisture levels that exceed the British Standard recommendations for resilient and timber floorcoverings, then a moisture mitigation system must be installed prior to the installation of the UFH system. For more detailed technical information on DPM systems for residual and continual rising moisture click here

^{*Covering the pipes or cables when installing resilient floor coverings as wooden floors or ceramic tiles can be applied flush with the pipe or wires.}

Precision groove cutting within screeds or screed boards

There are now innovative systems such as those pioneered by JK floorheating which allow underfloor heating to be installed within an existing screed. This is achieved by cutting grooves within the screed using a patented dustless “floor grinder” machine. The underfloor heating pipes are then installed within these channels. Once the underfloor heating pipes have been embedded within the screed different types of floors can then be installed using products from UZIN UTZ UK which have been tried, tested and certified.

Alternatively, if no screed is present, for example, UFC is required over wooden floorboards then pre-fabricated screed boards can installed and the channels grooved into the panels. It is important to note that JK floorheating have only tested the channel grinding with Fermacell® boards and no other pre-fabricated boards should be used. The underfloor heating pipes are then implanted within the panels. Different types of floor coverings can then be installed over the Fermacell® boards using products from UZIN UTZ UK which have been tested and guaranteed to be compatible.

The brand JK fermafloor derived from the collaboration between the three companies. The benefits of using this system are minimal floor elevation, thermal improvement and acoustic reduction potential yet the system is cost effective, sustainable and very efficient. For more information and benefits about these unique systems click here.

Install underfloor heating over floorboards

Installing floors over underfloor heating

It is best to check with the floor covering manufacture their recommendations for installing onto underfloor heating systems, but the following is a guideline for the different types of floor coverings. There are also some principals which apply to all flooring.

The underfloor heating must be fully commissioned and tested as described above. In all instances the screed should be dry before installing the floor covering. When installing wood floors the moisture reading must be less than 65 % RH (Relative Humidity) and for all other types of flooring the reading must be below 75% RH. UZIN provide a range of damp proof membranes which would allow floors to be installed if the reading are above these levels (click here for more information). Please also note that moisture protection is normally only possible at a lower RH threshold when underfloor heating is present.

A room temperature between 13 ºC to 18 ºC should be sustained 24 hours prior to installing the floor as well as 24 hours after the installation. During the fitting the surrounding temperature should be at least 18 ºC and the floor temperature must not drop below 15 ºC.

Installing ceramic / stone tiles over underfloor heating

The heating should be switched off and the tiles must be installed with flexible adhesives and grouts to compensate for any thermal movement. Once the tiles and grout has been installed the underfloor heating should not be switched back on for at least 5 days. After this time, the heating can be switched on and temperature slowly increased 5°C a day until the desired temperature is reached. It is also important to ensure that the surface temperature throughout the installation does not exceed 27°C.

Installing carpets over underfloor heating

The underfloor heating should be switched off 2 days prior to the installation of the carpets. Once installed the heating should not be put back on for at least 2 days and peak temperature should be avoided for another 7 days. It is also important to ensure that the surface temperature throughout the installation does not exceed 27°C.

Installing vinyl over underfloor heating

The underfloor heating should be switched off 2 days prior to the installation of any resilient floor coverings such as vinyl or linoleum. Once installed the heating should not be put back on for at least 2 days and peak temperature should be avoided for another 7 days. It is also important to ensure that the surface temperature throughout the installation does not exceed 27°C.

Installing luxury vinyl tiles over underfloor heating

The underfloor heating should be switched off 2 days prior to the installation of the LVT. Once installed the heating should not be put back on for at least 2 days and peak temperature should be avoided for another 7 days. It is also important to ensure that the surface temperature throughout the installation does not exceed 27°C.

Installing wood over underfloor heating

The underfloor heating should be turned off for a minimum of 4 days before the wood floor is installed. The humidity and temperature within the area should also be maintained, and it is also important to ensure that the surface temperature throughout the installation does not exceed 27°C. After the wood has been installed, do not switch the underfloor heating back on for at least 3 days. When turning back on, set 1°C above the surrounding temperature and each day increase by 1°C until the required temperature is achieved. It is also important to note that each variety of wood has a different thermal resistance and thermal conductivity. The thickness of the wood also influences the heat transfer.

Installing resin over underfloor heating

The heating should be switched off before the resin is installed. After the resin has been installed the underfloor heating should not be turned back on until the resin has chemically cured normally within 7 days. After this time, the heating can be switched on and temperature slowly increased by approximately 5°C a day until the desired temperature is reached. It is also important to ensure that the surface temperature throughout the installation does not exceed 27°C.