Underfloor heating floor Coverings do's & don'ts

It is important to remember that any material (except tiles) laid over a warmed floor will have an insulating effect.  The insulating effect will reduce the output into the occupied space and raise the temperature of the floor structure beneath.  This is easily compensated for at the design stage, thus the reason for needing to know the proposed final floor covering.  Generally speaking any of the normal accepted floor coverings are suitable for use with underfloor heating, that is carpet and underlay, hardwood, laminates, vinyl and of course tiles.

Another important point that is very rarely considered is that floor heating opens up a new world with regard to floor coverings.  All the traditionally 'cold' coverings such as hardwood, laminate or tile are of course now warm underfoot.  These materials are also a lot easier to keep clean and are less likely to harbour carpet mites and dust.  The Begetube system will always be designed with the final floor covering taken into consideration.

It is not recommended that softwood flooring or cork tiles are used over floor heating, If in doubt please get in touch.

Before laying any final floor covering you should ensure that the floor structure is completely dry.  Under normal conditions it can take as long as 6-9 months for the moisture to naturally be expelled from a concrete screed.  This would obviously jeopardise your build schedule so you can speed this process up by running the floor heating for 2 weeks at a low temperature (25-30°C) after the screed has cured.  This will help remove the remaining moisture from the screed.

Once you are happy that the screed is dried, you can then lay your final floor covering.  Ensure the floor heating has been turned back off for at least two days before commencing this work.  This will stop floor adhesive 'going off' too quickly.  Once the final floor covering has been laid, leave for another two days before warming the floor, again at the low temperature.  The temperature can then be slowly increased up to the maximum for the type of floor construction over the course of a week.

Carpet and Underlay

The thermal resistance of carpets and underlay are measured in tog values, (1 tog= 0.1m²K/W) The higher the tog value, the higher the insulating effect, therefore it is preferable to choose carpet and underlay with low tog values.

Recent research has shown that the open weave of most carpets does not restrict the flow of heat from underfloor heating to any great degree.  Underlay and foam backed carpets will restrict the flow of heat.  When selecting an underlay or foam backed carpet for use over underfloor heating, the tog value should be ideally less than 1.5 tog.

Check with the carpet supplier regarding suitability for use over underfloor heating.  It is worth noting that some carpets alone go to over 2.5 tog.  Tog ratings of various underlay's range from 0.36 tog to 1.01 tog (generally sponge types).  Latex foam, heavy duty sponge can go as high as 2 tog while felt can be as high as 2.5 tog. If in doubt, please get in touch.

Vinyl sheet floor covering

Always follow manufacturers installation notes.  Vinyl sheet will not allow moisture to pass through it, particular care must be taken to ensure that the screed has been properly warmed and dried out prior to laying vinyl.  Turn the floor heating off for 2 days prior to sticking the vinyl down, leave off for a further 2 days to allow adhesive to set.  The same applies to a tiled floor when using tile adhesive and tile grout.  It is recommended that you use specific adhesive products which are suitable for use with underfloor heating.  These products will have a higher temperature rating and will be flexible.

Hardwood Floor Coverings

Can be either solid hardwood or engineered boards with hardwood laminate.

Solid Hardwood

Wood is a natural product and will be affected by both heat and humidity.  When wood absorbs humidity it will swell, and subsequent drying will cause shrinkage.  Timber flooring should be supplied kiln dried to approx 6-9% moisture content, it is advisable to loose lay the timber in the area where it is to be fitted so that it can acclimatise.  This will take approx 7 days.  Before laying, check the moisture content of the screed with a moisture meter and ensure it is below 4%.  The hardwood floor should be laid with the floor heating on giving a surface temperature of approx 20°C.  If the hardwood is being glued down, this should be done on a cool floor and ensure the correct adhesive is used (one suitable for use with underfloor heating) Begetube will always recommend that hardwood is floated over the screed instead of being glued down. This allows the hardwood to expand and contract.  When floating a hardwood floor most manufactures recommend a thin foam layer between the hardwood and screed, this is perfectly acceptable, do not use the thick foam type sheeting which is sometimes supplied.  Always refer to the timber floor manufacturers fitting guides and if in doubt contact Begetube UK.

Engineered Boards (Laminates)

This type of flooring is made up of layers of plywood or MDF under the hardwood finish.  It is a much more thermally stable product and will not react to heat or humidity to the same degree as solid hardwood.  Moisture readings and laying procedures are the same as hardwood, but always follow manufacturers recommendations.  After installing a timber floor the underfloor heating can be slowly raised to full operating temperature.  Final surface temperature of the timber floor should not exceed 27°C.  Always inform the floor covering supplier that his product is to go over underfloor heating.

Tiles

Floor tiles come in many different forms, the common types are ceramic, quarry, stone and marble.  All of these materials are ideal for fitting over floor heating as the resistance to the flow of heat energy is insignificant.  As with all other floor finishes it is important that the floor screed has been properly dried by running the floor heating at a low temperature until all moisture is expelled.  Before fixing the tiles the heating should be turned off and left to cool for two days, once the adhesive is set then the floor can be slowly raised up to temperature over a period of days.

Do not use cork or rubber tiles over floor heating.