What type of hardwood flooring to use?
When installing hardwood flooring over underfloor heating, engineered wood flooring must be used and not solid wood flooring. Engineered wood flooring can withstand significant fluctuations in temperature because it is made up of multiple layers of wood making it more dimensionally stable than solid wood flooring. Engineered wood flooring is available in a wide variety of species, finishes and styles, and once installed it would be almost impossible to tell the difference between engineered wood flooring and solid wood flooring by sight alone.
Things to consider before using underfloor heating
The whole of the chosen room or area has to have underfloor heating rather than in individual sections. This is so that the wood flooring is heated evenly, otherwise one part will expand and contact at a different rate to another, which may cause damage to the floor. However, if there are different zones in a property that are both using the same flooring but underfloor heating is not required in each part, then an expansion gap needs to be left between them to let the floor expand and contract independently. The expansion gap can be covered with a flooring accessory such as a T moulding.
Prior to installation of the flooring
Prior to installation of the hardwood flooring the sub floor should be clean, level, dry and dust free. The underfloor heating should be commissioned and running for a minimum of seven days before the screed sub floor is moisture tested. The temperature of the underfloor heating should be gradually increased on a daily basis (2ºC per day) until the maximum temperature is reached. To ensure the screed is fully dry it should be moisture tested with a concrete floor moisture meter.
The reading should be below 6% MC (Moisture Content) before any hardwood floor is installed. If the screed is still not dry after seven days then it should be left to dry naturally using the underfloor heating system and a de-humidifier if necessary. However, be careful not to dry the screed out too quickly, otherwise it may crack.
Installation of hardwood floor over underfloor heating
The underfloor heating system should be switched off during the installation of the wooden flooring. The engineered wood flooring needs to be glued down with a full surface bond (not lines of glue), using a flexible flooring adhesive, to allow the floor to expand and contract as the temperature generated by the underfloor heating rises and falls. If using a low tog underfloor heating underlay then the engineered wood flooring can be floated or loose laid. Nails or screws should not be used during the installation of the wooden floor in case they puncture the underfloor heating pipes.
After installation of the flooring
The maximum temperature of underfloor heating should be 26ºC. This means the surface temperature of the hardwood flooring, not the air temperature of the room. The best way to control this temperature is by using a thermostat. However, remember that when the thermostat cuts the temperature off it may still rise a couple of degrees before it cools down, so allow for this when setting the thermostat. Once the hardwood floor has been installed the heating should be switched on and the temperature slowly increased to the maximum of 26ºC (surface temperature of the wood) by approximately 2ºC every day.
Quick checklist for UFH (underfloor heating)
• Engineered wood flooring must be used with UFH
• Glued down or floated over a UFH underlay
• Whole room / area should have UFH (not just part of a room)
• UFH should be commissioned and running for at least seven days before installing a hardwood floor
• The screed should be clean, level and dry before installing a wooden floor
• UFH must be turned off during installation of a wooden floor
• Maximum temperature of UFH is 26ºC (surface temperature of the wooden floor)
Increase UFH temperature slowly by around 2ºC per day once the hardwood floor has been installed
