When it comes to under floor heating, ceramic tiles are not the only solution for floor covering any more. Pre finished two layer parquets or thermo treated three layer parquets are becoming a standard in west European construction sites. To avoid any problems regarding flooring materials and under floor heating, there are certain standards and procedures that have to be followed so that floor heating system may function perfectly.
Screed layer (cement layer or estrich) has to be made according to proper construction standards; the screed surface has to be flat, smooth and firm and screed itself compact and dry. Hot water pipes have to be laid at least 3 cm beneath the screed surface in order to prevent uneven heating throughout the whole floor surface. Areas with thinner screed layer will cause wood to lose more of its natural humidity which can result in cracks and other deformities in wood. Maximum screed humidity for wooden floors must not exceed 1.5%.
To obtain optimal results, screed has to rest for 3 to 5 weeks before installing the parquet floor, depending on the thickness of the screed layer (approximately 10 days for each cm of screed thickness).
The next step is to try out the under floor heating system. The heating starts with the water temperature of 25°C. Every next day water temperature has to be increased by 5°C until water temperature reaches 55°C (the temperature is not to be changed during night). Water temperature has to be kept on maximum for as many days as screed layer is thick in centimetres (1 cm = 1 day of maximum heating). The heating system than has to be cooled down in the same pace as it was heated. When this process is over, measured screed humidity must be within standard levels (under 1.5 % for cement screed). If the screed humidity exceeds 1, 5% the floor has to be heated again to 40°C until required screed humidity values for wood flooring are obtained. Only then the floor can be covered with parquet. Wood parquets require minimum floor temperature of 18°C measured on the surface of screed with relative air humidity under 60%.
Floor primer and glue used in parqueting should be of good quality and appropriate for floors with under floor heating. Having laid the parquet, under floor heating system can be activated. Floor temperature has to be kept under 25°C!
The thermal resistance for floor coverings on floor heating systems should not exceed 0.15m²K/W. During the making of the main plan, it is necessary to know the type of flooring which will be used, because that will also decide the type and way of installing the pipes. If the floor is covered in layers of different materials, the total thermal resistance is calculated by adding up thermal resistances of each material.
As wood reacts to changes of the surrounding climate, floor heating can cause increased drying during the heating period. This can result in deformations and cracks in the parquet. To avoid this problem room temperature should be kept at 18 to 21°C with air humidity of 50 to 55% which will allow parquet to keep its natural humidity. It is important to know that between two heating seasons certain small cracks can appear in the wood which is normal. If they have a more or less proper scheme on the surface, this process should be considered as normal.
In order to avoid cracks in the parquet it is recommended not to cover it with carpets or other thermo insulating materials. Maximum allowed wood humidity in multilayer parquets is 5-9% according to EN 13226, 13227, 13488, 13489, 13629 standards.