Footstep insulation - what it is and how to install it correctly

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What is step isolation and why it is even discussed around the manifold

Step isolation is a strip of insulating foil (usually made of foamed polyethylene or a similar material with closed cells), which is inserted into the expansion joint around the room perimeter during the installation of floor heating and anhydrite or concrete screed. At first glance, it seems to be a minor detail that many associate exclusively with acoustics — hence the name "step" (dampening footstep noise between floors). In the context of manifolds and heating systems, however, step isolation has a second, equally important function: expansion. Precisely this function is the reason why it is also discussed in the section dedicated to manifolds and their accessories — without properly placed step isolation, damage to the manifold itself, the piping, and the screed may occur due to thermal expansion of the floor.

During floor heating, significant temperature changes occur — anhydrite or concrete screed heats up from room temperature (about 18–20 °C) to operating temperature, which can reach 27–29 °C on the surface and even more in the screed layer near the pipes. This temperature change causes volumetric expansion of the screed — the material literally expands and contracts. If the screed were to adhere directly to the wall, partitions, columns, or the built-in manifold cabinet in the floor or wall, it would transfer stress to the structure, cause cracks in the screed and finishes, and in the worst case, damage the manifold connections.

Two functions of step isolation — acoustic and expansion

In practice, we often encounter the situation where investors and less experienced contractors associate step isolation only with the anti-noise standard (especially in apartment buildings, where footstep noise damping between floors is required according to STN EN ISO 717-2). This is correct, but only half the truth. In floor heating, the strip of step isolation placed around the room perimeter also performs the function of an expansion joint — it allows the screed and floor to "breathe," i.e., to change volume without pressing against walls, doors, thresholds, columns, or the manifold itself.

Why it is important precisely around the manifold

The floor heating manifold is usually installed in a wall cabinet, from which the connections (usually through the bottom or back panel of the cabinet) run directly into the screed. If step isolation is missing or carelessly installed at the point where the screed surrounds the pipe transition from the cabinet to the floor, stress occurs precisely at this sensitive point — where the pipes are most strained by bending and where the risk of mechanical damage to the joint or the pipe itself is greatest. In practice, we have encountered cases where the lack of expansion in the area of the transition caused a micro-crack in the screed right next to the cabinet and a gradual loosening of the manifold's mounting after two heating seasons.

From the diagram, the principle is visible: step isolation creates a flexible gap between the rigid structure (wall, manifold cabinet) and the screed, which expands when heated. Thanks to this gap, the movement of the screed is "absorbed" into the compressible insulation material and does not directly affect the cabinet or the connections.

What step isolation is made of and its parameters

The most common material is cross-linked foamed polyethylene (PE) with a closed-cell structure, which has good damping and expansion properties and is also resistant to moisture — which is important because it comes into contact with wet screed during its installation and remains permanently in the floor structure. Common thicknesses on the market are 3, 5, 6, 8, and 10 mm, with 6–8 mm being most frequently used in residential construction with floor heating. In the product range, you can find, for example, Step Isolation 1.5 m; 6 mm — 75 m pack or a smaller pack of Step Isolation 1.0 m; 6 mm — 12.5 m pack, which differ in the height of the strip (1.5 m vs. 1.0 m) and the total length in the pack.

Why there are different strip heights (1.0 m and 1.5 m)

The height of the step isolation strip is selected according to the total height of the floor construction — i.e., the sum of the thickness of the thermal insulation, the system board, the screed, and the wearing layer. In typical residential renovations, where the floor construction reaches 8–12 cm, a 1.0 m high strip is sufficient, which is easily trimmed and the excess part is cut off after the screed hardens. In new constructions with a thicker thermal insulation layer (e.g., in low-energy or passive houses, where the thickness of polystyrene under the pipes reaches 100–160 mm), a higher 1.5 m strip is more suitable to ensure the insulation reaches from the subfloor up to the level of the future wearing layer with sufficient reserve.

How to properly install step isolation — step by step

Proper installation of step isolation is a simple, yet often underestimated operation. From dozens of implementations we have had the opportunity to observe or consult with customers, it follows that the most frequent errors occur precisely at this seemingly trivial step.

1. Preparation of the subfloor and room perimeter

Before laying the system board or fixing the heating pipes, it is necessary to clean the perimeter walls, corners, door thresholds, columns, pipe shafts, and all vertical structures that will be in contact with the screed. Step isolation is glued or fixed along the entire room perimeter, including around the manifold cabinet, if it is installed at floor level or if the connections run directly into the screed.

2. Laying the isolation strip

The strip is laid vertically, with the lower edge directly on the thermal insulation (system board) or on the waterproofing, resting against the wall so that it covers the entire future height of the screed and extends beyond the planned wearing layer — ideally 1–2 cm higher than the final floor. This overhang is cut off with a sharp knife or plane just below the level of the tiles or floor covering after the screed has hardened.

3. Joining and corners

In room corners, the strip is overlapped or cut at an angle to avoid gaps through which cement or anhydrite mix could seep to the wall. A common rule from practice: in a corner, it is better to have a slight overlap of two strips than a gap — excess material can be cut, but a gap would cause direct contact between the screed and the wall and loss of the expansion function precisely at the most critical location (corners are most stressed during thermal expansion).

4. Fixing

The strip is fixed either with double-sided adhesive tape to the base rail of the system board or simply held in place by its own flexibility and the pressure of the screed. In some system boards, there is a groove or rail on the lower part of the board into which the strip is inserted, mechanically securing it against shifting during the pouring of the screed.

5. Pouring the floor screed

During pouring, it is important to check whether the strip has slipped, broken, or turned inward, as such damaged insulation loses its function. Construction workers should be careful when pouring and spreading the screed to avoid pulling the strip with a trowel or float.

6. Trimming after hardening

After the screed has sufficiently hardened (with anhydrite, it is usually possible to walk on the surface after 24–48 hours, but full hardening takes weeks), the protruding part of the strip is cut precisely at the level just below the future wearing layer. This cut is then covered with a skirting board or filled with a permanently flexible sealant — in no case should it be filled with a rigid material (for example, a patching compound based on the same material as the tiles), as this would again eliminate the expansion function.

Expansion joint insulation in the context of a distribution box enclosure

A specific situation arises with distribution box enclosures that are embedded in the wall or mounted so that the bottom edge of the enclosure is at the level of the screed or just above it. These are typically products such as Wall-mounted distribution box enclosure N-MAX 1 - 450 mm, Wall-mounted distribution box enclosure N-MAX 5 - 1200 mm, or Wall-mounted distribution box enclosure N-KLASIK 2 - 535 mm. When installing these enclosures, it is important to consider that the connections either pass through the bottom panel directly into the screed or through the side/back panel into the wall and then descend into the floor near the wall.

In both cases, the same rule applies — where the screed meets the vertical structure (the wall on which the enclosure is mounted or the body of the embedded enclosure itself), the expansion joint insulation must be continuous. If the enclosure is embedded in the wall so that its bottom edge protrudes partially into the future screed area, we recommend also insulating this bottom edge of the enclosure, not just the wall next to it — otherwise, a "hard point" will form, which will cause similar problems during screed expansion as missing insulation next to the wall.

Practical example from implementation

In a standard project involving a family house, where the distribution box is installed in a technical room and the enclosure is mounted on the wall approximately 30 cm above the floor level, it is sufficient to run the expansion joint insulation in the usual way around the perimeter of the room, including the section of the wall under the enclosure — there is no need for any special solution, as the enclosure is not in direct contact with the screed. A different situation arises if the enclosure is mounted in a niche or partition so that its bottom edge is at the level of the future floor (for example, in a solution where the distribution box is located in a partition between the hallway and the bathroom) — in this case, the expansion joint insulation must also be run around the bottom edge of the cut-out for the enclosure to prevent direct contact between the screed and the metal or plastic frame of the enclosure.

Consequences of improperly placed or omitted expansion joint insulation

From consultations with implementation companies and from warranty cases, we can summarize the most common problems that arise from neglecting this seemingly insignificant part of the floor construction:

Cracks in the screed at walls and corners — the most common and visible problem, which appears already after the first heating season.
Cracks in the tiles or damage to the floating floor along the perimeter walls, since the tension from the screed is also transferred to the wearing layer.
Mechanical stress on connections at the transition into the distribution box enclosure — in extreme cases, even microcracks in the joints between the pipe and the fitting, which may result in minor water leakage, detectable only when the system pressure drops.
Transfer of noise and vibrations between floors, which is a problem especially in apartment buildings, where it may lead to non-compliance with acoustic standards at the time of handover.
Enhanced thermal bridges at the room edges, since the screed in direct contact with the wall transfers heat more efficiently into the structure than desired.

Repairs to these problems after the floor has been completed are usually significantly more expensive and complicated than properly placing the insulation strip for a few crowns during implementation — often the only solution is to cut a groove along the entire perimeter of the already finished floor and additionally fill it with flexible sealant, which is not always aesthetically or technically trouble-free with high-quality tiles or wooden flooring.

Material quantity — how to calculate consumption

Consumption of expansion joint insulation is calculated simply according to the perimeter of the room (or the total sum of perimeters of all rooms with underfloor heating or screed), with an additional allowance for overlap in corners and for possible errors during cutting — in practice, an allowance of approximately 10–15 % is calculated.

Example calculation: a room with a floor plan of 4 × 5 m has a perimeter of 18 linear meters. With a 10 % allowance, it is necessary to order approximately 20 linear meters of insulation. In an apartment with multiple rooms (for example, a living room, kitchen, hallway, bathroom, two bedrooms) with a total perimeter of around 55–60 linear meters, it is advisable to order a package with sufficient length — for example, Expansion joint insulation 1.5 m; 6 mm in a 75 m package reliably covers a larger apartment or a family house with an allowance, whereas for a smaller apartment or a single room (for example, only a bathroom and a hallway during a partial renovation), a smaller package such as Expansion joint insulation 1.0 m; 6 mm in a 12.5 m package is sufficient.

Type of room/area	Estimated perimeter	Recommended length with allowance	Suitable type
Bathroom (2.5 × 3 m)	11 lm	approx. 12–13 lm	1.0 m height
Living room (5 × 6 m)	22 lm	approx. 24–25 lm	1.0 or 1.5 m height
3-room apartment (total)	~50–60 lm	approx. 60–66 lm	1.5 m height (75 m package)
Family house (entire ground floor)	~90–120 lm	approx. 100–135 lm	1.5 m height, multiple packages

Expansion joint insulation and type of screed — anhydrite vs. cement screed

The principle of placing expansion joint insulation is the same for both types of screed, but the importance and sensitivity to errors differ. Anhydrite (flowable) screed has a higher coefficient of thermal expansion and expands more during heating, so the expansion joint along the perimeter is even more important with anhydrite than with a conventional cement screed. In addition, large areas without further expansion joints in the surface are often realized with anhydrite (unlike cement screed, where internal expansion joints are recommended for larger areas, for example in doorways) — this makes the functionality of the entire system even more dependent on the quality of the properly placed perimeter expansion joint insulation.

Common mistakes during implementation that we have seen in practice

Over the years of supplying components for floor heating, similar mistakes have repeated across various construction companies and DIY projects. It is worth listing them to avoid them:

Too low expansion joint - if the strip does not reach above the level of the future wearing layer, the screed during pouring will "overflow" over the top edge and create direct contact with the wall precisely at the top part, which is most often overlooked.
Gaps in the corners - they occur due to inaccurate cutting, and the screed mixture flows directly to the wall, locally disrupting the expansion function.
Displacement or tilting of the strip during screed pouring - this happens especially when the strip is insufficiently fixed, and workers accidentally shift it with trowels or floats during spreading the mixture.
Omission of insulation around penetrations and embedded elements - typically precisely around embedded manifold cabinets, around columns, around chimney bodies, or around staircase structures.
Additional "pouring" of the expansion joint with rigid material - after laying the tiles, the joint is sometimes filled with ordinary grout for aesthetic reasons instead of flexible silicone or polyurethane sealant, which completely eliminates the expansion function.
Underestimating the thickness of insulation for thicker screeds - for larger areas or for screeds with a higher expected thermal load (e.g., industrial halls, large heated floors in showrooms), it is recommended to consult with the designer on the thickness and possibly also the width of expansion joints beyond the standard 6 mm.

Recommendations for selection and purchase

When selecting expansion joint insulation, it is mainly recommended to follow the overall floor construction and the scope of the implementation. For standard apartments and houses with a typical construction (thermal insulation 30-60 mm, screed 45-65 mm, wearing layer), a thickness of 6 mm is fully sufficient, which is also the most commonly available and cost-effective. When choosing the height of the strip, follow the sum of all layers of the floor construction including a reserve of 1-2 cm - for standard constructions up to 10 cm, a height of 1.0 m is sufficient, while for higher constructions or in case of uncertainty (e.g., the thickness of the wearing layer has not yet been finally decided), it is safer to choose a height of 1.5 m; the excess part can always be cut, but insufficient height cannot be added later.

When ordering the quantity, it is better to count with a slight reserve. The leftover material can be used for another room or for a future renovation, while purchasing a small missing piece due to the lack of two standard meters is in practice an unnecessary complication, especially if the screed pouring is already in progress and the construction cannot wait for delivery.

Frequently asked questions

Is expansion joint insulation necessary in a detached house where there is no neighbor above or below?

Yes. Although the acoustic requirement between floors is not present in a detached house, the expansion function of the expansion joint is always necessary whenever a screed is implemented with floor heating or even without it. It is about protecting the screed and the structure from cracking due to thermal expansion, not just about acoustics.

Can expansion joint insulation be replaced with another material, for example, a mineral wool strip?

Technically, it is possible to use other flexible, water-resistant materials, but the standard practice and proven solution is precisely closed-cell polyethylene foam, which has the right combination of compressibility, resistance to moisture during screed pouring, and long-term durability in the floor structure. Mineral wool is not suitable, as it absorbs moisture when in contact with wet screed and loses its properties.

What happens if the expansion joint insulation sinks or slips lower during screed pouring?

If the strip shifts during pouring so that its top edge drops below the planned level of the wearing layer, the screed will come into direct contact with the wall at the top. In this case, it is necessary to cut the joint additionally after the screed has hardened (e.g., with an angle grinder with a thin disc or a special saw) all the way to the perimeter structure and fill it with flexible sealant to restore the expansion function.

Is it necessary to address expansion joint insulation around a wall-mounted cabinet above floor level?

If the cabinet is mounted higher above the floor and is not in direct contact with the screed, it is sufficient to run the expansion joint insulation standardly around the entire perimeter of the room, including the wall section under the cabinet. Special measures (e.g., sealing the bottom edge of the cabinet) are necessary only if the cabinet is embedded so that its frame or bottom edge is at the level of the future screed.

What is the difference between expansion joint insulation with a height of 1.0 m and 1.5 m apart from the price?

The difference is exclusively in the height of the strip, i.e., in the thickness of the floor construction that it can cover without the need for stacking or supplementation. A higher strip (1.5 m) is more universal and safer in case of uncertainty regarding the final floor construction, while a lower strip (1.0 m) is more economical for standard, well-known constructions up to about 10 cm.

Must the expansion joint insulation be cut immediately after the screed dries, or can it wait?

Cutting the protruding part is usually done just before laying the wearing layer (tiles, floating floor), not immediately after the screed hardens. There is no need to rush, it is important only not to forget this step before the final installation of the floor covering and baseboards.

Expansion joints in the screed area - when the perimeter expansion joint insulation is not enough

For larger areas or more complex floor plans, it is not sufficient to address expansion only around the perimeter of the room using expansion joint insulation - it is necessary to divide the screed area into smaller expansion units using internal (area) expansion joints. These joints are most often inserted at doorways, at the change of direction of heating circuits, at the transition between rooms with different pipe laying orientations, or at areas exceeding the recommended maximum dimensions (for cement screed, usually an area over 40 m² or a side length over 8 m; for anhydrite, larger integral areas are also acceptable due to the lower internal tension of the material, approximately up to 300-400 m² without the need for further joints, always according to the technical data sheet of the specific screed manufacturer).

A crucial technical detail that is often underestimated in practice: a heating pipe must not be run through an area expansion joint without protection. If a circuit must pass through a joint location (e.g., when connecting two rooms with one circuit through a doorway), the pipe must be protected with a protective sleeve (cladding) of at least 20-30 cm on each side of the joint, so that the pipe can freely move within the sleeve when the two parts of the screed move relative to each other, avoiding bending or cracking at the joint location.

The layout of expansion joints should be part of the underfloor heating project documentation already in the phase of designing distributors and circuits - this is precisely why it is worth aligning the position of the joints with the routing of individual circuits so that as few pipes as possible cross them and it is easy to apply protection without unnecessarily complicating the installation. A combination of properly placed perimeter expansion strip insulation and functionally designed expansion joints is the basis of a floor that can withstand repeated thermal cycles of the heating season without cracks and without unnecessary stress on the distributor and its connections.

Summary

Expansion strip insulation is a simple, inexpensive, yet key element of the floor construction with underfloor heating, which ensures two important effects - acoustic damping and, above all, the expansion function protecting the screed, floor covering and connection to the distributor from damage due to thermal expansion. Proper placement means an uninterrupted strip around the entire perimeter of the room, including corners, transitions and recessed elements, with sufficient height exceeding the level of the future walking surface, without gaps and without later filling with rigid materials. When planning the implementation, it is worth allowing for an appropriate amount of material and choosing the appropriate thickness and height of the strip according to the overall floor construction - for standard implementations, a thickness of 6 mm is sufficient, and the choice between height 1.0 m or height 1.5 m according to the total thickness of the construction. In combination with a properly selected distributor and suitable distributor cabinet, a system is thus created that will reliably and trouble-free serve many heating seasons without the risk of cracks, leaks or mechanical damage caused precisely by neglected expansion.

Do you have a question about this topic?

Not sure or dealing with a specific situation in your home? Write to us - we are happy to advise.