UNDER FLOOR HEATING GUIDELINES
IMPORTANT: If you have, or are thinking of having underfloor heating, please read the following guidelines carefully. We are not only experts in wood flooring, but have also installed dozens of wet, and dry underfloor heating systems, so our experience in this area is vast.
Not all wooden floors are compatible with underfloor heating, so make sure that the floor you intend to use is compatible before you buy.
MULTILAYER OR SEMI SOLID WOOD FLOORING
PLEASE NOTE: In our opinion Multi-Layered Floors are not suitable for use with underfloor heating. We will however provide the same guarantee as other companies for this type of floor when fitted over under floor heating.
So why do we think that multi layered floors are not suitable for under floor heating ? It’s all to do with the construction of the multi layered boards. Multi layered boards are made up of a plywood base and a solid wood top layer that is bonded to the plywood. By bonding the solid wood to the plywood, the natural movement of the solid wood layer, as it takes on or loses moisture, is minimised by the stability of the plywood which is fine if you are able to maintain your environment between 45% and 60%. The problem arises when the living environment falls below 45% relative humidity, a very common occurrence in houses with underfloor heating, and the solid wood layer dries out so much that it starts to crack, split and in some cases peel away from the plywood. This all happens because the plywood is so stable that it does not move at all, in other words it is too stable for the solid wood top layer. For more details check with TRADA.
ENGINEERED WOOD FLOORING
These floors are “real” engineered floors, not to be confused with multi layered floors. They differ from the multi layered floors in that their construction is a three layered construction. They are made up of a top layer of solid wood, a core layer fir strips and a stabilizing base layer of pine. The grain of the wood on each layer runs at 90 degrees to the grain on the layer either directly above or below. This is what gives the product it’s stability, wood when it expands or contracts moves across the direction of the grain.
These products are more suitable for use over underfloor heating for two reasons. Firstly the moisture content of the wooden floor when it leaves the factory is between 6% and 8% which means the product can easily cope with environmental conditions down to 30% relative humidity which are quite common in houses with underfloor heating. Secondly the construction of the board allows for some minor movement in the lower layers to compensate for movement in the top layer at very low relative humidity thus preventing splits, cracks and de lamination.
SOLID WOODUnder no circumstances can you fit a solid wood floor over underfloor heating. The answer is that wood is hygroscopic, it takes on moisture at high relative humidity and expands and loses moisture at low relative humidity and contracts. The range of environmental relative humidity that a wooden floor will have to cope with when fitted over underfloor heating is simply too great for a solid wood floor to cope with. The floor would show huge gaps and possibly cupping during the heating season and would expand and possibly buckle during the summer months.
When fitting wooden floors over underfloor heating please follow these basic rules.
1. The underfloor heating system must have been pressure tested and left running for a minimum of two weeks prior to installation of a hardwood floor.
2. The moisture content of the screed must be less that 75% relative humidity.
3. The surface temperature of the screed should be tested prior to installation and should not exceed 27 degrees centigrade.
4. A floor probe should be fitted to regulate the surface temperature of the screed.
5. Before fitting, the underfloor heating should be turned off.
6. The new hardwood floor should be fully bonded to the sub floor using MS Polymer adhesive.
7. On successful installation the underfloor heating can be turned back on after 24 hours and the room brought up to heat slowly.
8. Always turn the underfloor heating up or down slowly over a period of days to prevent damage to the hardwood floor.
9. Always maintain environmental conditions that are appropriate for the floor that you have fitted.