common mistakes when installing insulation boards on the substrate
Why is your floor heating not heating or cracking? Hidden causes in insulation boards
Imagine a situation that repeats dozens of times a year in our practice at atria.sk: the customer has a floor heating system installed, starts the heating season and realizes that the room temperature does not rise even by one degree. Alternatively, after the first freeze, cracks begin to appear in the concrete. Often the boiler, distribution unit or even the quality of the pipe is blamed. In reality, however, the problem is often hidden deeper – directly in the foundation of the system, i.e. in the laying of the insulation boards.
The insulation board is not just a "padding" between the concrete screed and the base structure. It is a key thermal resistance that determines the direction of heat. If this layer does not work properly, the entire heating system loses efficiency, energy consumption rises to unreasonable levels and the risk of damage to the building increases. As a technician with experience in installation sites, I can tell you that 80% of the problems with the efficiency of floor heating are related to what happens under the pipe, before the concrete is poured. In this article, we will look at the most common installation errors that even experienced craftsmen make, and show you how to avoid them using the right technique and quality materials.
Mistake No. 1: Ignoring the separation between insulation and wall (acoustic bridges)
The most fundamental, yet most often overlooked mistake is not laying the edge strip or laying it insufficiently along the entire perimeter of the room. When you place the insulation boards directly on the concrete base and then pour the screed on top of them, an acoustic and thermal bridge is created between the screed and the masonry walls. When heated, the concrete screed expands. If it has no space for this expansion at the edge, the pressure is released where the weak point is – this often leads to cracking of the screed or detachment of the tiles.
This phenomenon is visible in the diagram below, where we compare the correct section with the incorrect solution:
In practice, I have encountered cases where installers used pieces of foam or cardboard to fill the gap. That is not enough. Always use a specialized edge strip that compensates for thermal expansion. This strip should extend above the level of the final screed so that you have it exactly at the level when tiling or laying floating floor.
Mistake No. 2: Wrong choice of thickness and density of boards for a given type of subfloor
Many customers think that the thicker the board, the better. That is not true. There is an optimal ratio between the thickness of the insulation board and the load-bearing capacity of the subfloor. If you have floor heating in an apartment on the second floor above a neighbor's apartment, your goal is not only thermal insulation, but mainly **footstep insulation**. A thinner board with higher compressive strength is sufficient here, which ensures that steps across the floor are not transmitted to the lower apartment.
On the other hand, in a ground floor house where the subfloor is soil or old concrete, you need a board that can withstand the load from the screed and furniture without rotting or deforming over time. If you use a soft board with low strength on a heavy coating, depressions may form after a few years, which can cause tile cracking. On the other hand, if you use a too hard and thick board in an area where you do not have enough height (e.g. renovation), you may get into problems with doors or stairs.
For standard apartment applications, where protection against footstep noise is important, special footstep insulations are ideal. For example, our Footstep insulation - 1.5m; 6mm - pack 75m is designed to meet noise protection standards while maintaining minimal space loss. For larger areas, where faster laying and high stability are needed, I recommend variants in 1.0 m packaging, such as Footstep insulation - 1.0m; 6mm - pack 50m, which provides an excellent balance between strength and thermal resistance.
Mistake No. 3: Lack of continuity and leakage of joints (thermal bridges)
Another common mistake is not understanding the importance of sealing the joints between the individual boards. If you place the boards next to each other with a gap, even a small one, heat will escape downward instead of upward. This is not just a matter of energy loss, but also of local cooling of the concrete, which can lead to condensation formation and subsequent rotting processes in the structure. The correct technology requires that all joints are glued with a special tape or sealed with adhesive that creates a hermetic seal.
It often happens that installers use ordinary insulating tape, which dries out and peels off over time. In such a case, passive zones are created in the system where heat "leaks". To achieve maximum efficiency, the surface of the insulation must be undisturbed and connected into one whole. This is critical especially in systems where a grid layer is used, because this layer serves as a stabilizing frame for the pipe. If the base under it is uneven or has cracks, the pipe can move, which causes uneven heat distribution.
Mistake No. 4: Ignoring electrical wiring and junction boxes
Floor heating often works in combination with other systems, for example with electric heating or smart home systems. One of the most common mistakes is incorrect placement or installation of junction boxes for electrical wires. These boxes serve to safely connect the wires and connect the thermostatic sensors. If they are placed too close to the heating pipes without sufficient protection, or if they are improperly embedded in the insulation board, short circuits or mechanical damage to the wires during screed pouring can occur.
Most professionals know that junction boxes must be resistant to moisture and heat. However, in practice, I have seen cases where installers used cheap plastic boxes that deformed and shorted the contact when heated. The result was failure of the entire control system. It is also important to maintain a distance from the heating pipes to avoid overheating the insulation around the box. For safe and functional connection, I recommend using quality products such as Junction boxes for electrical wires - 150cm, which are designed for these specific conditions and ensure long-term functionality.
Mistake No. 5: Improper preparation of the subfloor and its cleanliness
Do not forget that the insulation board is laid on an existing subfloor. If this subfloor is dirty, greasy or contains brick and concrete fragments, the insulation board will not lie flat. This leads to the formation of air pockets under the board, which act as thermal insulators and disrupt heat transfer. In addition, sharp fragments can pierce the foil or self-supporting layer over time, leading to water or vapor leakage.
In practice, I have seen installers simply "sweep" the floor with a broom and start laying down the boards. That is not enough. The subfloor must be cleaned, leveled, and if necessary, treated with a primer, especially if it is very porous. The main goal is to achieve a smooth surface on which the insulation boards will lie firmly and evenly. If the subfloor is uneven, you must level it, otherwise you risk the boards shifting during the screed pouring, creating "waves" in the system that can cause uneven heating.
Mistake No. 6: Incorrect Arrangement and Overlapping of Boards
Another technical mistake is the incorrect arrangement of boards. The boards should be laid in such a way that the joints between them do not cross (so-called "cross joints"). If the joints meet at one point, a weakened zone is created there, which can crack under load. The correct technology requires that the joints between the boards overlap in an "alternating" pattern, similar to bricklaying. This ensures even load distribution and increases the stiffness of the entire system.
This principle is clearly visible in the following diagram, which illustrates the difference between a bad and a good arrangement of boards:
This detail is often overlooked, yet it has a crucial impact on the system's longevity. If the joints overlap, a zone is created that is more prone to deformation. Therefore, it is important to ensure the correct arrangement of boards right from the laying process.
Practical example from practice: The "Cold Floor" Case
A case that taught me a lot happened in a family house in a region where the client requested a low price. The installers used cheap insulation boards without edge strips and without gluing the joints. Two weeks after the heating was turned on, cracks appeared in the kitchen floor and the temperature in the living room was 3 degrees lower than in the other rooms. During the inspection, we found that the insulation boards had deformed under the pressure of the screed and air pockets had formed. Heat could not spread evenly and part of the energy was lost downward. The correction required removing the entire floor and reinstalling it with quality boards and the correct laying technology. This case shows that saving money at the beginning can lead to multiple times higher costs later.
System functionality check and maintenance
Even if the system is installed correctly, it is important to regularly check its functionality. This is especially true for systems that have integrated pump modules. If the pump module is incorrectly set or if there is air in the system, the entire heating system may fail. Therefore, it is important to have an understanding of how your system works and how to maintain it in good condition. For example, if you have PUMP MODULE SET - for distribution units - 6/4"x1", it is important to regularly check the pressure and temperature to avoid problems.
Maintenance should include checking the tightness of the joints, checking the functionality of the thermostatic sensors, and possibly refilling the gas in the system. If you have questions about maintenance or need advice, do not hesitate to contact our experts. We are here for you to ensure that your system will function long-term and efficiently.
Mistake No. 7: Incorrect placement of thermal bridges at structural elements
A critical point that is often overlooked is the penetration of heat through load-bearing structures, such as columns or load-bearing walls, which extend into the concrete screed. If these elements are not insulated separately from the floor system, local thermal bridges are created, which "pull" the heat toward the colder parts of the building and reduce the heating efficiency in their vicinity.
This detail is crucial especially in modern apartment buildings, where we often encounter monolithic structures. If the insulation board is laid only on the surface without surrounding the column, heat from the pipe will escape directly into the massive column, which acts as a cooler. The result is uneven heating of the room and increased energy consumption. Therefore, it is essential to cut out space around all load-bearing elements and fill it with the same insulation board, which will have the same thickness as the rest of the subfloor.
Mistake No. 8: Ignoring expansion joints on large areas
Another common mistake is ignoring the need for expansion joints when laying insulation boards on large areas. When the concrete screed heats up, it expands. If the entire area is one solid piece without the possibility of expansion, internal stress is created, which leads to cracks. This applies not only to the screed, but also to the insulation board layer itself, if it is laid on a large area without expansion joints.
According to standards, it is recommended to divide areas larger than 40 m² or exceeding 6 meters in length using expansion joints. These joints should be filled with a soft material that compensates for the expansion. If this step is skipped, the screed may start to crack after the first heating period, which can lead to damage to the floor and disruption of the entire system's functionality.
Below is a schematic showing how to properly divide a large area into smaller sections:
This approach is the basis for long-term floor stability. When dealing with large areas such as living rooms or storage spaces, it is essential to follow the rule of dividing them into smaller sections. This ensures that thermal expansion is compensated and prevents damage to the structure. Always make sure that expansion joints are filled with suitable material that allows movement without damaging the insulation boards.
FAQ: Frequently asked questions about insulation board installation
Do I need to glue the insulation boards together?
Yes, it is essential. Joining the boards with adhesive or special tape prevents heat loss and ensures the system functions as a single unit. Without this step, heat will be lost and the heating efficiency will significantly decrease.
What thickness of insulation board is suitable for an apartment and a house?
For apartments, a thickness of 2 to 3 cm is usually recommended, with pressure resistance also being important. For ground-floor rooms in houses, a thickness of 4 to 6 cm is recommended to ensure sufficient thermal separation from the ground. The exact thickness should always be determined based on the type of subfloor and thermal insulation requirements.
Why does the connection box fail and how to fix it?
Failure of the connection box is often caused by poor-quality material or incorrect placement. If the box deforms or the contacts loosen, a short circuit may occur. Repair requires removing the screed and replacing the box with a higher-quality model. Before installation, it is important to check that the wires are properly connected and that the box is protected from moisture.
What is the difference between the 6/4x1 pump module and other types?
The difference lies in the pipe diameters and the pump performance. The 6/4x1 module is intended for smaller systems with 6/4 mm pipes, while other types may be designed for larger diameters. Choosing the correct module depends on the size of the system and the water flow requirements.
Is it necessary to install an edge strip?
Yes, an edge strip is essential to compensate for the thermal expansion of the screed. Without it, the screed may crack and the tiles may detach. The strip should be installed around the entire room and should extend above the level of the screed.
How often should the function of safety thermostats be checked?
Inspection should be carried out at least once a year, preferably before the start of the heating season. The inspection includes verifying the correct temperature and pressure settings, as well as checking the functionality of the thermostat itself. If you notice any problems, address them immediately.
Conclusion: Investing in quality pays off
Installing underfloor heating is a complex process where every detail matters. Insulation boards are not just a passive element but a key component of the system that determines its efficiency and lifespan. To avoid problems such as cracks, high energy costs, or system failure, it is essential to follow the correct installation technology and use high-quality materials. Do not neglect the preparation of the subfloor, gluing of joints, or installation of connection boxes. These small details are what distinguish a professional system from an amateur solution.
We hope this article helps you understand the importance of proper insulation board installation and avoid common mistakes. If you have more questions or need advice when choosing materials, do not hesitate to contact us. Our team of experts is here for you so you can enjoy the comfort and efficiency of underfloor heating without worries.
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