Tiles

Floor for underfloor heating: floor tiles, vinyl or laminate and layer composition

Almost any covering is suitable for underfloor heating, but not all are equally effective. Floor tiles conduct heat best, while vinyl and laminate require products designated for underfloor heating and a lower surface temperature. The thermal resistance of the entire composition, moisture of the screed before installation, and the procedure for the first activation are crucial.

Prepared by: TGB Kúpeľne team, bathroom showroom in Senec since 1991updated 9. 11. 20265 min read

Illustrative image: large-format tiles on underfloor heating in the living room

Underfloor heating warms the entire surface, and the covering above it acts as a layer through which heat must pass. The less it obstructs, the faster it heats the room, and the lower the water temperature or power can be. We describe how to choose the heating for the bathroom in the articles Underfloor heating in the bathroom and Electric underfloor heating. Here we address the floor above it.

Thermal resistance: the number that matters

Each covering has a thermal resistance R in m²K/W – the higher it is, the more it obstructs heat. The EN 1264 standard for underfloor heating assumes that the thermal resistance of the covering above the heating does not exceed 0.15 m²K/W. This value is referenced by flooring manufacturers and their association EPLF. It is important that the entire composition is considered – covering, underlay, and adhesive.

You can find the value in the technical data sheet of the covering and underlay. For example, Coretec states 0.0318 m²K/W for the Pro Core range and 0.066 m²K/W for the 8 mm thick Sound Core. Simply add the values of the covering and underlay and compare them with the limit.

Comparison of coverings for underfloor heating

EN 1264 also restricts the surface temperature of the floor for comfort – in the living area to 9 K above room temperature. However, for vinyl and laminate, there is a stricter limit for the covering itself.

Tiles for underfloor heating

Tiles are the simplest choice for underfloor heating. They conduct heat, are not affected by higher temperatures, and are water-resistant in the bathroom. To ensure durability, several rules must be followed:

• Adhesive – flexible tile adhesive specified by the manufacturer for underfloor heating, applied over the entire surface without voids. A void under the tile can result in cracking when heated and cooled.
• Expansion joints – around the perimeter of the room and in larger areas also according to the project. Expansion from the screed is also transferred to the tiles.
• Electric mat – laid in adhesive or under a thin screed under the tiles. How to connect and measure it is described in the article Electric underfloor heating. You can find mats in the online shop in the category Electric underfloor heating.

Vinyl and laminate on underfloor heating

Vinyl and laminate can be installed on underfloor heating if the manufacturer explicitly states so. The differences are mainly in surface temperature and underlay:

• Surface temperature – for vinyl usually a maximum of 27 °C, for laminate for example Skandor 26 °C. The heating regulation must ensure that their floor does not exceed this – for electric heating, a floor sensor helps.
• Underlay – only one that the covering manufacturer allows for underfloor heating, with low thermal resistance. A thick insulating underlay would stop the heat.
• Before laying – turn off the heating. For PVC coverings, instructions state to completely turn it off at least 2 days before laying, allowing the covering to acclimatize in the room.
• After laying – for example, Barlinek allows heating to be turned on no sooner than 48 hours after installation for the Next Step vinyl.

Whether vinyl is suitable for the bathroom and how to lay it is described in the article Vinyl flooring in the bathroom. You can find vinyl floors in the online shop in the category Vinyl floors.

Layer composition for water-based heating

With electric heating in the bathroom, the structure is thinner – the mat goes directly into the adhesive or under the screed on the existing substrate. During renovation, the floor only rises by a few millimetres.

Moisture of the screed and first activation

The most common mistake with underfloor heating is laying the covering on a damp screed. Technical data sheets for levelling compounds and screeds specify these residual moisture limits before laying:

Moisture is measured by the floor installer using the carbide method CM. The first heating of the screed is done by the heating technician according to the technical data sheet – for example, Stavmat states that for screed W410, the temperature should be increased by no more than 5 °C per day. How long the screed takes to dry and where it fits in the order of work is described in the article Apartment renovation: order of work.

Common mistakes

• Thick insulating underlay under vinyl or laminate – heat does not pass through.
• Covering on damp screed – vinyl and laminate will warp, adhesive will not hold.
• Exceeded surface temperature with vinyl or laminate – the covering deforms and loses warranty.
• Voids under the tiles – cracks when heated.
• Missing expansions around the perimeter and in the area.
• Sudden activation after laying instead of gradual ramp-up.

Sources: EN 1264 (thermal resistance of covering up to 0.15 m²K/W, surface temperature in terms of comfort) according to EPLF and manufacturers' instructions; technical data for Coretec (thermal resistance, surface temperature), Aspecta, BerryAlloc and Rimatex (vinyl up to 27 °C), Skandor (laminate up to 26 °C), Barlinek Next Step (activation after 48 hours); technical sheets for Ceresit DC and AS 1 Rapid and Stavmat STline W410 (moisture of screeds, covering pipes, expansions, ramp-up of heating); instructions for laying PVC (turn off heating before laying).

Terms in the dictionary: Underfloor heating · Gres (porcelain stoneware tiles) · Vinyl floor (SPC) · Flexible tile adhesive (C2TE S1) · Screed · Waterproofing