Substrate
A floor construction consists of several layers that together form the solid base of the floor. The order of these layers may vary, usually depending on the land and the specific situation, but generally speaking they contain comparable elements. When underfloor heating or a new floor finish is placed, it is important to know what is underneath these layers.
Floor construction
Here is a short explanation of the eight general layers of a floor construction;
Layer 1 – Foundation: The foundation may not officially form part of the floor construction, but it is often poured simultaneously with the floor plate. Foundations come in all shapes and sizes, but the most common kind is strip foundation. This consists of channels of about one metre deep into which a layer of concrete rubble or crushed stone is dumped, followed by reinforcement cages that are fixed in the rubble. Besides channels for the foundation, sewer pipes are sometimes also placed in the channels and then filled up with soil.
Layer 2 – Floor plate: The floor plate is an important part of the floor construction and serves as a solid base for the house. It is made of reinforced concrete and typically has a thickness of about 10 centimetres. To protect the reinforcement from corrosion, a damp proof membrane is usually also applied.
The concrete for the floor plate is often poured at the same time as the foundation channels. After the concrete has been poured, it is compacted by vibration to remove any air pockets. This makes the concrete even stronger. In case of renovation or expansion it is essential that the new floor plate is not resting on the old foundation, but rather just barely floats above it by means of edge insulation. The floor plate itself consists of concrete, a mixture of cement, water, sand, gravel and/or crushed stone, and has a rougher finish.
Layer 2A – Crawl space: Houses with a crawl space have a different floor construction. The crawl space is located between the foundation and the floor insulation. Rather than placing the floor insulation directly onto the floor plate, the floor insulation is placed on floor beams that serve as support structure. This create a space between the floor construction and the bottom of the foundation. This space may vary in height, but it is usually high enough for an adult to move on their hands and knees and gain access to e.g. plumbing or for other maintenance works.
Layer 3 – Utility lines: Utility lines for e.g. the supply of water and electricity are placed on top of the concrete plate. Usually the water pipes are placed first, because these are generally bigger and less flexible. In addition, the incline also plays an important role in proper functioning. The electric cables are often placed last, as they tend to be more flexible and do not need a specific incline, so there is more room to manoeuvre.
Layer 4 – Floor insulation: The floor insulation is placed on top of the floor plate and the utility lines. A layer of concrete, also called a fill layer, is poured over the top of the lines to even the floor out for insulation. The type of floor insulation can vary from one country to another. In some countries the insulation is the “peel” of the house and rests under the floor plate.
Floor insulation is often made of pressure-resistant EPS or XPS material that can carry a lot of weight. Another option is sprayed PUR-insulation, which gives more padding. The benefit here is that no separate fill layer is needed and it fits well around the pipes. However, after hardening this PUR layer does have to be sanded down.
In some cases, there is also the option of an insulated screed. This approach combines floor insulation and screed in one layer, which has certain benefits for existing buildings.
- It is important to note that, depending on the country, older houses may not have floor insulation. For example, in the Netherlands houses were subjected to energy efficiency guidelines from 1983, while in Germany most new houses after 1973 were insulated, though this was not mandatory. In England floor insulation was specifically mandated since 1995. Policy with regards to housing insulation was only narrowed down since the 90s, when governments started placing certain prerequisites on roof insulation as a condition for being hooked up to the electricity grid.
- Floor insulation is often seen as less important than other types of house insulation, such as roof and wall insulation, because flooring generally exhibits less heat loss. As explained in this section, a floor construction, even without insulation, consists of multiple layers and is provided with thick materials (such as the floor plate) that are often placed directly on the soil. This is in contract to walls and ceilings which are subjected to much larger differences in temperature.
Layer 5 – Underfloor heating: Traditionally underfloor heating is applied to the insulation layer, with the option of using both wet and dry installation methods. The wet method entails the use of steel nets or tacker panels to apply the heating pipes in a snail shell pattern onto the insulation. With the dry method the insulation layer itself contains grooves into which the heating pipes are placed, after which a heat-conducting plate is placed on top of the pipes before the screed is poured. The JK® system diverges in this step, as the underfloor heating is applied after the screed is placed.
Layer 6 – Screed: The screed is poured on top of the insulation layer, with or without integrated underfloor heating. Usually the screed is a sand-cement mixture, around 5 cm thick, to which fibres are added for additional strength. However, there are also more advanced screeds, such as anhydrite floors. These flow better, have chemical binding properties and other traits that make them suitable for certain applications. The screed ends up with a smooth finish.
Layer 6A – In-ground underfloor heating: In-ground underfloor heating, like the JK® system, is installed after the screed is placed. Contrary to other underfloor heating systems, the JK® system ensures the pipes are much closer to the floor surface and are not covered by a screed. Therefore, the JK® system is installed at a different stage from other methods. Often the JK® system is only installed after the building has been fully constructed and its internal layout is known. This offers the builder the option of a bespoke installation, taking into account specific furnishings such as a kitchen island, windows, or other built-in design features. In-ground underfloor heating offers more flexibility in design and installation, allowing the JK® system to be tailored to the specific requirements of the space and decoration.
Layer 7 – Levelling: Before the floor finish can be placed the floor itself must be levelled. This is especially important in cases where the screed shows irregularities of more than 3 mm deep. A levelling compound is used for this, and its minimal and maximal thickness depends on the product and its composition – it is usually between 0.5 mm and 30 mm. If there are big gaps or irregularities these have to be filled first with a repair compound.
Layer 8 – Floor finish: The floor finish is the last step and it is placed directly on top of the screed, the JK® system, or the levelling compound. The floor finish can be floating or adhesive, depending on the type of finish. It is essential that the floor finish be placed after the screed has cured.
As previously mentioned, the floor construction can vary widely depending on the land and the specific situation. Many especially older buildings can have a simple construction with a pure foundation and a thick concrete layer (Layers 1 and 2) onto which the floor finish is placed. In some cases, this concrete floor is directly on the soil, without additional insulation layers.
The lack of floor insulation with such floors is not a problem for the installation of the JK® system, because in our system the heating pipes are much closer to the floor surface and are not covered by a screed. This way the heat is distributed directly to the floor, which results in efficient and rapid heating of the space. The fact that the pipes are adjacent to the floor surface compensates for the lack of insulation and ensures a good heat distribution. This makes the JK® system ideal for older buildings. JK is proud to report that the JK® system is regularly installed in centuries-old cottages and farmhouses in for example Scotland and the Netherlands, where our system has been successfully applied.
Up next: Screeds
