If heat comes from a floor, it warms the whole room evenly and less energy is needed to get the desired temperature. If you are about to install underfloor heating (UFH), whether it is a new build or an existing home, you need to think of a screed mix that will cover it. In this article, we will talk about what needs to be taken into consideration, what preparation is required, and how to get as much of your UFH as possible when choosing the best screed possible.
The most common type of UFH is warm water underfloor heating, which is based on a warm water circulating in steel, copper or PVC pipes. These are laid evenly across the room floor. You can also meet with an electric UFH which is used pretty often too but because of the much higher energy needed it is used usually only in small spaces – such as a bathroom.
Starting from a bottom, the subfloor is either a concrete slab or a beam & block which is insulated by a waterproof membrane. The membrane is then covered with either a thermal insulation layer of polystyrene or mineral wool (f.e. Kingspan. Xtratherm etc.). If needed, another vapor insulation will be fitted over it and then the fitting of the pipes can begin. These are usually laid on a floor evenly and fitted to the underlay by clips (picture below). Only after everything is prepared actual ready mix screed is placed. When the screed is dried, the flooring of your choice will be fitted.
It is very important to keep the recommended thickness of a screed, which covers the pipe. The thickness will have a significant impact on how the actual UFH will distribute the heat. The ideal thickness when the traditional sand cement screed is used is somewhere between 65 to 75 mm. If the screed with additives is used (fibre which allows for a screed to be stronger) a minimum of 50 mm might be used. The same rule applies to ground and upper-level floors.
There are two main types of screed used. Dry screeds and Self-levelling screeds. While dry screeds are more traditional, cheaper and used in smaller areas, self-levelling screeds offer an advantage when used in vast industrial or commercial areas while being more expensive. Dry screed mix ratio is 1:3-5 = cement and sand. This is mixed with water and fibre additives to avoid cracking. Also, other additives can be added to ensure fast drying. Self-levelling screeds also known as liquid screeds (or flowing screed), made of calcium sulphate, sand, water and other chemicals, is simply poured or pumped on the area and it spreads and achieves the desired level by itself.
When the underlay and the UFH were installed properly and while keeping certain conditions, any flooring can be placed over the UFH. In terms of high thermal conductivity, the best flooring to use in ceramic and natural stone tiles, PVC and textile flooring. Least preferred is wood. However, if you still want to use a wooden floor, it can be implemented as a floating floor. Classic separation pad, which could reduce the thermal conductivity, is necessary to replace with a special board or flooring needs to be glued directly on the substrate with a polyurethane adhesive. Anyways, always follow the instructions of a producer.
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