Wood on underfloor heating – questions and answers

Before the heating season comes, find out how much you know about installing wooden floors with underfloor heating. Are you planning this type of investment? This text will provide you with the knowledge you need.

What does it mean that wood is hygroscopic?

Hygroscopicity is the susceptibility to absorb moisture. Wood is a hygroscopic material, which means that it reacts to environmental conditions, such as humidity level and temperature. This should be remembered both in the context of long-term storage of purchased boards, as well as their installation and subsequent use.

What is most important: the method of preparing the surface, the type of flooring, or perhaps choosing the right specialist?

A properly prepared substrate is essential, but the material itself and the competences of the person who will lay it are also very important. It is best to entrust the installation of the floor to a person with experience and knowledge, as well as appropriate tools, thanks to which it will be possible to check, for example, the moisture of the screed. How to find a competent person? Companies offering wooden floors often cooperate with specialists worth recommending. When talking about important factors, it is worth adding that even the conditions (such as temperature and humidity) in the room and the substances used during work are important. For example: an incorrectly selected glue will cause the wood to become detached from the base.

Do you really need to read the flooring instructions?

Of course! If after reading the document there are any ambiguities, it is best to contact the seller or manufacturer. Remember that the appearance of the floor, and therefore the comfort of household members and guests, depends on the method of installation and the proper use and care of the wood.

How long does it take to install wood on a heating installation?

Installing a wooden floor is a time-consuming process. Apart from installing the boards, you also need to take into account the time needed to heat the floor. The process, which lasts about a month, is a necessary step before installing wood on the heating system.

What is a screed and how to prepare it before installing the floor?

A screed is a screed, i.e. an underlay for the floor. The most popular ones are cement, gypsum and anhydrite. Remember that a floor should not be installed on a freshly made screed - the subfloor must be heated and its surface should be smooth, even and sufficiently durable. The maximum humidity of a cement screed is 1.8%. on the CM scale (and when using vapor barriers - 0.3% on the CM scale). The appropriate humidity level for anhydrite screed is 0.3%. on the CM scale.

The temperature of the screed during floor installation should be between 15 and 18 degrees Celsius. It must be maintained for at least 5 days after installation is completed.
After this time, it can be raised (by 1 or 2 degrees per day) until the desired temperature is achieved. The maximum contact temperature (the surface temperature of the cement screed measured 3 days after setting the temperature) of the cement screed is 28 degrees. (Data from Chapel Parket Polska).

What is substrate heating? Why is it worth recording this activity?

The floor is heated to remove moisture from the subfloor. If the screed is not heated, excess moisture will be absorbed by the wood. As already said, the process takes about a month.

- Preheating involves maintaining a specific temperature in the room where the floor is to be installed. Just follow the instructions and document the activities in a special protocol. The necessary documents (heating instructions and protocol) should be delivered to investors together with the floor. This process should under no circumstances be omitted, because it is much easier and cheaper to prepare the floor well before installation than to repair the effects resulting from the lack of heating of the substrate - emphasizes Sebastian Kos, an expert at Chapel Parket Polska, which offers oak floors, including those intended for installation on "underfloor heating".

It is worth remembering that for some manufacturers, the mentioned protocol is an important element of the floor warranty, so this activity should not be ignored.

Can solid wood be installed over heating?

- It is not recommended to install solid wood on a heating installation. The thermal resistance of solid wood is too high, making heating ineffective and uneconomical. This type of material is more susceptible (than laminated wood) to the "work" of wood and to temperature changes - emphasizes S. Kos.

What is special about laminated wood in the context of underfloor heating?

It is a material that does not have a uniform structure, but consists of several layers arranged in such a way that the rings of the layers are perpendicular to each other. Thanks to this structure, the "work" of wood is significantly limited. The layered material is more resistant to changes in humidity and temperature, and does not significantly inhibit the flow of heat, which is why it is recommended for underfloor heating. It is worth knowing that in many European countries, including Poland, laminated wood that can be installed on underfloor heating is called an engineering material.

What aspects should you pay attention to when choosing a floor for heating?

The first is the material's thermal conductivity coefficient, which expresses its thermal insulation properties. The higher its value, the more heat will flow through the raw material. The unit of thermal conductivity is W/mK (Watt per meter-Kelvin).

The value of heat conduction resistance also provides valuable information. This concept covers the degree of thermal insulation of a material depending on its thickness and thermal conductivity coefficient. Simply put, the lower the thermal resistance, the greater the amount of heat that will be conducted through the material. According to the DIN 4725 standard, materials whose thermal conductivity resistance does not exceed 0.15 m ² K/W (square meter - Kelvin/Watt) can be installed on water underfloor heating.

Attention! Thermal resistance depends on the thickness of the material, but thicker boards will not always result in greater heat losses. Proof of this is the installation of 20 mm thick floors on the underfloor heating. Therefore, you should not pay attention to the thickness of the wood itself, but to the value of the thermal resistance of the selected floor. It is best to ask the manufacturer or seller about this indicator.

Another important variable is the wood shrinkage coefficient, which can be used to determine the material's resistance to moisture. The coefficient represents the average shrinkage of the material as a percentage when its moisture content changes by 1 percent. The lower its value, the better; a low shrinkage coefficient means that the wood is more stable, so the "work" of the wood will be limited.

Can I give up expansion joints?

An expansion joint is a deliberately created gap running along the walls, allowing the wood to "dilatate" - expand and contract. You cannot opt out of doing so. To increase the comfort of using the floor, use expansion strips.

The information was created in cooperation with experts from Chapel Parket Polska, which offers planed and sanded layered floors (boards, strips and cassettes) that can be installed on underfloor heating.