Contrary to popular belief, there are few restrictions on the floor coverings that are suitable for use with underfloor heating. Carpet, timber and tiles (ceramic and natural) all work well as long as some simple guidelines are followed.

Tiled floors

The group of floor coverings consisting of ceramic tiles, natural stone, slate, marble, limestone, flagstones and any similar material work extremely well with underfloor heating as they are good thermal conductors.

The key to success with these products is a firm or solid sub-base for them to sit on. This is usually a concrete screed, but can be a suspended beam and block or timber joisted floor as long as it is well supported and has no movement.

Screeded floor constructions

Because the underfloor heating causes the floor to act as a huge radiator, it expands and contracts with the varying amounts of heat present. In the screed, this is absorbed by an expansion gap and edge insulation; any tiles fitted on top may well expand at a different rate to the screed and should, therefore, also have an expansion gap around the perimeter of the room (the bigger the room, the bigger the gap should be) – this will usually be covered by a skirting board. Flexible adhesive and grout should also be used when fixing down tiles to help mitigate expansion.

Suspended timber floor constructions

The nature of suspended timber floors means they are, inevitably, more prone to movement than screed. This said, much can be done to minimise movement and allow successful use of tiles. Well fitted joists are extremely strong and, when covered with a minimum of 18mm (22mm is recommended) staggered chipboard or ply panels with glued joints that has also been screwed down securely, any movement is much reduced. When using this floor construction it is vital to use flexible tile adhesive and grout.

Timber floors

Timber flooring is generally supplied in two forms: solid wood planks available in various widths and types of timber, and engineered board which includes everything from a thin veneered panel available from most DIY stores, to specialised solid wood laminates.

Because wood is a natural product it reacts to the surrounding atmosphere and this should be borne in mind when selecting the correct timber flooring for your home. Engineered board, made up of layers laminated together often with the wood grain running in opposite directions in each layer, is an inherently stable product. Solid timber is also suitable for use with underfloor heating, although narrower boards are recommended as they expand and contract less with atmospheric changes. Hardwood flooring is available in a wide variety of finishes, widths, thicknesses and qualities to suit the style required. Where thin laminates are used over a suspended timber floor, a chipboard or ply sub-deck will be necessary for stability.

Care should always be taken to make sure conditions on site are suitable for both acclimatising and laying any timber floor. Moisture levels in a building prior to laying a wood floor are critical. To avoid excessive movement of the finished wood floor the tradesmen laying the floor must be satisfied that the screed, timber flooring and internal construction (wall and ceiling plaster) are suitably moisture-free, which may mean leaving boards unpacked in a dry room for several weeks. Laminate floors and engineered boards do not require acclimatisation as their moisture content will have been corrected before lamination.

Battening is a commonly used to fix timber floors down. This can be set into concrete floor to give a fixing point for screws or on top of joists when plated underfloor heating systems are present. Care must be taken not to damage the floor heating pipe when nailing or screwing into the battens.

As with screeded floors, always leave an expansion gap around the edge of the room; typically 15mm. This will allow the floor to expand and contract with atmospheric changes and will usually be hidden by skirting.

Carpets

Despite popular misconceptions, it is perfectly possible to fit carpet over underfloor heating, it is just a question of choosing the correct combination of carpet and underlay for your project.

The thermal resistance value of carpet and underlay is measured in togs with thickness, density and composition all affecting the tog rating achieved. To get the best performance from your underfloor heating, the combined value of the carpet and underlay should not exceed 2.5 tog.Typically, the tog value of an 80%/20%, wool/nylon carpet will be between 1.5 and 2.0 and the tog value of underlay varies enormously so it is perfectly possible to source a combination to suit your needs. Quality manufacturers will have technical information on their products available to customers.

When used over screeded floors, carpet and underlay can be stuck down to avoid uneven heating pockets, although this is rarely an issue.

For further information on floor coverings, please see the Carpeting Floors and Hardwood Floors information sheets available as pdfs from the downloads section of the website. Alternatively, telephone Nu-Heat on 0800 731 1976 where a member of the Sales Team will be happy to discuss the alternatives.