Fixing of underfloor heating pipes - clips, strips and arches
Fixing underfloor heating pipe – clips, strips and arches
When we look at underfloor heating from the customer's perspective, most attention goes to the selection of the right pipe, the spacing of the pipes or the thickness of the insulation. Pipe fixing – that is, the way you physically keep the pipes in place during concrete pouring – often remains an overlooked detail. Yet this decision directly determines whether your final screed layer will be even, whether the pipes will not float in the pour or shift into corners where you don't want them. In practice, I have seen jobs where due to poor or no fixing, the installer had to walk around the entire morning pressing the pipes down, so the concrete crew wouldn't embed them crooked. That is neither fun nor economical.
This article is exclusively about fixing elements – their types, method of use, selection for a specific base and practical details from real jobs. The related topic – the selection of insulation, the comparison of system boards and grid foil, or the actual installation process from insulation to pouring – is covered in separate articles in the Knowledge Center.
Why fixing matters more than it seems
The underfloor heating pipe made of PE-RT or PEX has a standard diameter of 16 or 17 mm (external), sometimes 20 mm. It is a flexible material that has a shape memory – after winding on a reel, it wants to twist back. When you unroll it and lay it on foil or insulation, without fixing, it will rise, shift and change the radius of the bends. When such a loosely laid pipe is approached by a concrete crew, the result is unpredictable: the pipes can shift during walking, the concrete can lift them, or conversely, compress them in places where it will later cause mechanical stress. Even coverage with concrete – ideally at least 30 mm above the top of the pipe – is a condition for proper heat transfer and system longevity.
Fixing therefore has three basic functions:
- Maintain spacing – to keep the pipes in the planned spacing (typically 100–300 mm) and not create densely packed or empty areas
- Maintain height – to keep the pipes at the required depth in the screed and not let them sink onto the insulation or rise to the surface
- Fix the arches – to prevent the turning points of the pipes from spreading and to maintain the minimum bending radius (usually 5× the external diameter)
Depending on the base you have (system board, grid separation foil or bare insulation), there are various fixing solutions available. Let's look at them one by one.
Three basic fixing systems – overview and comparison
Each of these three approaches has its place. In practice, they are combined – for example, strips on straight sections and arches on turns, or clips everywhere if it's a system board with nops. Let's look at each element in more detail.
Fixing clips – clip system for straight sections
Clips (also called clips or clamps) are simple plastic elements that are pressed through the pipe and fastened into the insulation or base. Our Pipe fixing clip – 50 mm; straight is a typical representative of this type. The dimension 50 mm in the name refers to the spacing of the clip tips, which are embedded into the EPS – this defines the point fixing with precise anchoring.
How clips work in practice
The clip has the shape of the letter Ω (omega) at the top, where the pipe is attached, and at the bottom two tips or legs, which are pressed into the soft insulation material (EPS, PIR). No tool is needed for installation – just your hand or a light finger pressure. The clip clicks into place and holds the pipe in an exact vertical position. When the concrete or anhydrite comes, the pipe remains in place.
Spacing of clips on straight sections: standard 300–500 mm (i.e., 2–3 clips per meter of pipe). On arches, the spacing is reduced to 150–200 mm, because here the elastic force of the pipe wants to straighten. For larger pipe diameters (20 mm) or stiffer materials, I recommend 300 mm even on straight sections – in winter, when the EPS is colder, the pipe is stiffer and the force to pop the clip out is greater.
On which base clips work
Clips are primarily intended for soft insulations: EPS (polystyrene) of various densities, mineral wool with sufficient surface strength, or combined bases. Clips are not used on system boards with nops – the pipe is held by the nopped grid itself. On grid foil (without significant depth of nops), clips can work, but the tips must reach into the EPS under the foil, not just into the foil itself.
Example from a job: A family house, base layer 80 mm EPS 100, above it separating grid foil as protection and orientation grid. Pipe PE-RT 16×2 mm, pipe spacing 150 mm. On straight sections we use clips every 350 mm, on arches every 180 mm. Consumption of clips per 100 m² area with 150 mm spacing and a clip every 400 mm on average: approx. 400–500 pcs. With larger pipe spacing (200 mm) and fewer arches: around 300 pcs.
Fixing strips – fast and even fixing on flat surfaces
Pipe fixing strip – 16–18 mm; 1 m/100 is a product sold in packages of 100 pieces (i.e., 100 meters of strip in total). The strip is 1 meter long and corresponds in cross-section to pipes with an outer diameter of 16 and 18 mm.
Principle of the fixing strip
Unlike a fixing clip, which fixes the pipe at a single point, the strip holds the pipe along its entire length in regular supports. It is a flat plastic profile with protrusions (holders or grips) at regular intervals – typically every 50 mm. These protrusions snap around the pipe after it is inserted. The result is that the entire 1 m of pipe is fixed with one element.
The strips are laid perpendicular to the direction of the pipe and are anchored to the base (EPS or system board) – either with clips, screws, or by pushing in. Spacing of the strips on the surface: typically 500–600 mm. This means that each pipe touches each strip, which with a pipe spacing of 150 mm and a strip spacing of 500 mm results in almost an ideal grid fixing.
When strips are more advantageous than clips
Strips are faster to install on large flat areas – when laying 200 m² of parallel meanders, you don’t want to mark and push in a thousand individual clips. Instead, you lay a row of strips and simply press the pipes into them. Another advantage is that the strip directly determines the pipe spacing – if the supports are every 50 mm, you can lay the pipes at 50, 100, 150, 200 mm, etc., without having to measure.
A disadvantage of strips is curves – they cannot be used directly there. Curved sections must be solved with clips or curved elements. A combined approach (strips on straight sections, clips on curves) is very common and efficient in practice.
Example from a job: New construction, 3 rooms with areas of 18, 14 and 9 m². Projected spacing of 200 mm. The installer laid strips every 500 mm perpendicular to the pipe direction, and pressed all the pipes into each strip at once. On one side of each room, there were curves, where clips were used. The total fixing time (excluding pipe laying) was under 2 hours for all three rooms. The same result with clips would have taken 3.5–4 hours.
Fixing curves – fixing the turning points of meanders
A curve is a special fixing element designed exclusively for the turning points of the pipe. PEX pipe fixing curve – 16–18 mm forms a pre-shaped semicircle with a precise radius, into which the pipe is inserted and snapped. The result is a U-bend with a controlled, uniform radius without the risk of pipe breakage.
Why the bending radius is critical
A PEX or PE-RT pipe has a minimum allowed bending radius – for a diameter of 16 mm, it is usually 80–100 mm (5× outer diameter). If the pipe is bent too sharply, the cross-section deforms (flattens), which increases hydraulic resistance and can damage the material structure in the long term. In everyday practice, when an installer manually shapes a bend without a curve, the risk of an overly sharp bend is high – especially in colder weather or with a stiffer type of pipe.
The curve eliminates this problem: the radius is determined by the element's design and the pipe cannot exceed it. At the same time, the curve holds the pipe in position – without it, the bend would open after laying and the pipes would separate.
Practical use of curves
Curves are installed at the edge of each meander. The number of curves depends on the area and the pipe spacing. For a room of 4×5 m with a spacing of 150 mm, you will have approximately 26–28 U-bends, i.e., 26–28 curves. Important: curves fix the pipe, but they are not anchored to the base themselves. Therefore, it is necessary to additionally install 1–2 clips just before the entry into the curve, so that the entire bend does not push sideways.
Bends are supplied for specific pipe diameters – do not insert a 16 mm pipe into a 20 mm bend, as it would slide freely inside. The bend type available from Atria is designed for 16–18 mm pipes, covering the most commonly used diameters in apartment and house installations.
Separation foil and metal tape – the basis for fixing
Before starting the pipe laying and fixing, the subfloor must be properly prepared. In the case of a dimpled foil system, the first step is to unroll and join the foil strips. Separation dimpled foil – 0.1×1030 mm; AL – 50 m² serves simultaneously as a separation layer (prevents grout from penetrating into the insulation), as a reflector (the aluminum surface reflects thermal radiation upwards), and as a guiding grid (the dimpling helps maintain the pipe spacing).
The foil strips are laid with an overlap of 50–100 mm and joined with metallic tape – 55 mm × 50 m. This connection is not just aesthetic – it ensures that during the concrete pouring, the grout does not penetrate between the strips and wet the insulation. The metallic tape has an aluminum surface, so it holds even in environments with mild humidity. A width of 55 mm is sufficient to cover the joint solidly and adhere on both sides.
Warning: the foil itself does not secure the pipes. It serves only as a base layer. Fixing elements (clips, strips) must pass through the foil and grip the EPS underneath. This is why the clip tips must be sufficiently long – at least 30–40 mm – to reliably embed into the EPS beneath the 0.1 mm thick foil.
Combination of fixing elements in a real project – practical procedure
The following example shows how fixing is implemented across the entire floor area of a family house. Floor plan: 3 rooms + bathroom + corridor. Total area approx. 95 m². Pipe spacing 150 mm (rooms), 100 mm (bathroom – higher required thermal density). Pipe PE-RT 16×2 mm. Subfloor: EPS 100S thickness 80 mm + dimpled separation foil.
- Subfloor preparation: EPS boards are laid tightly next to each other (without gaps), joints are sealed with tape. Dimpled separation foil strips are unrolled with an overlap of 80 mm, joints are sealed with metallic tape along the full length of the joint.
- Strap placement: On flat room areas, fixing straps are laid perpendicular to the planned pipe direction, with a spacing of 500 mm. Straps are pushed through the foil into the EPS (minimum 30 mm length of the tips).
- Pipe laying: The pipe is unrolled from the reel and pressed into the clips of the strap in one movement along the entire row. At the end of the row, the pipe is turned using a fixing bend and continues in the opposite direction.
- Bends at turns: At each end of the row, a fixing bend is installed, and two clips are pushed in just before and after the bend.
- Bathroom: Due to the smaller spacing (100 mm) and irregular shape, the entire bathroom is fixed with clips every 300 mm, without straps.
- Inspection before pouring: The entire circuit is pressurized to 4–6 bar and left under pressure during the concrete pouring. The installer walks over the area once more to check if any clip has come loose (usually 1–2 clips loosen under mechanical load).
Total consumption of fixing elements for this project: approx. 380 clips, 80 straps (= 80 m), 62 bends. Fixing installation time (excluding the actual pipe laying): 2 workers × 3 hours.
Most common fixing errors – what we repeatedly see in practice
In the article Common mistakes in pipe laying for floor heating and how to avoid them in the Knowledge Center, we cover mistakes in the entire installation process. Here we focus only on those directly related to fixing.
Too few fixing elements
The most common mistake – the installer saves on clips and places them every 60–80 cm. This is too few. After the concrete pouring, wavy pipe patterns can be seen in the finished screed, indicating uneven pipe coverage and thus uneven thermal performance. Correct frequency: 300–500 mm on straight sections, 150–200 mm on bends.
Clips only in the foil, not in the EPS
The clip tips must pierce the foil and anchor in the EPS. If the clips are too short or the installer does not press them in sufficiently, they are held only by the foil. At the first mechanical load (installer stepping), the pipe will loosen. Check: try to pull the pipe – a properly installed clip should offer noticeable resistance.
Bends without additional clips
A bend itself carries the pipe's flexibility force in the turn, but it does not hold by itself in the subfloor. Without 1–2 clips right next to the bend, the entire U-turn shifts sideways. During the concrete pouring, this can cause the bends to protrude from the surface or the turns to shift.
Unsealed joints of the separation foil
If the joints of the dimpled foil are not sealed with metallic tape, during the concrete pouring (or anhydrite pumping), the grout may penetrate under the foil and wet the EPS. Hardening in the EPS causes thermal bridges and increases the floor load without a project.
Fixing on too soft insulation
On mineral wool with low surface strength (soft type), clips do not anchor reliably – the tips are pushed sideways. In this case, it is necessary to use either a system board or straps anchored with longer tips or anchor screws. The topic of insulation selection is covered in the article How to choose an insulation board for floor heating – thickness, material and requirements.
Material calculation – how many fixing elements do I need?
Before ordering materials, it is good to make a simple estimate. The following values apply to a standard installation with a meander laying pattern:
| Area [m²] | Pipe spacing [mm] | Clips [pcs] | Strips [m] | Bends [pcs] |
|---|---|---|---|---|
| 20 | 150 | 120–150 | 18–22 | 14–16 |
| 50 | 150 | 280–350 | 40–55 | 32–38 |
| 100 | 200 | 350–450 | 70–90 | 50–60 |
| 100 | 150 | 500–620 | 85–110 | 65–75 |
These numbers are approximate. For more complex floor plans (more corners, recesses, columns), expect an increase of 15–20 %. It is always better to have 10 % more fixing elements on site than to stop work due to a shortage.
Important note about strips: the package fixing strip – 1 m/100 contains 100 pieces = 100 meters. For an area of 100 m² and a spacing of 500 mm between strips and a room width of 5 m, you will need 200 strip segments = 200 m, i.e., 2 packages.
Fixing for spiral laying vs. meander
The way of pipe laying directly affects the requirements for fixing elements. The two basic methods – meander (snake) and spiral (spiral) – differ not only in hydraulics, but also in fixing requirements. We will discuss this topic in more detail in the article "What pipe diameter and spacing do I need for floor heating?", here we just briefly summarize from the perspective of fixing:
- Meander: Regular U-turns at the walls, straight sections inside. Bends can be easily predicted and pre-installed. Strips work well on straight sections. Number of bends: 1 for each U-turn.
- Spiral (double snake / spiral): The pipe runs to the center and back, all bends are in corners and at the walls. Bends are quarter-circle (90°), not half-circle. Standard fixing bends are not suitable for this type – here you rely only on clips and a higher number of clips in corners. The advantage is that the straight sections (running to the center) are ideal for strips.
Special cases – stairs, terraces, renovations
Floor heating is not only for flat areas in new buildings. In practice, we also encounter more complicated situations where fixing requires a different approach.
Renovation (thin screed, low structural height)
In renovations, structural height is limited – sometimes to 60–80 mm total including insulation. This means thinner EPS (30–50 mm) and a thinner pipe (e.g. 12×2 mm instead of 16×2 mm). Clips must be shorter (pins 20–25 mm), or special clamps for thin layers are used. Fixing strips may be problematic in such a thin layer – their height must not exceed the top level of the pipe, otherwise they would be embedded in the screed as hard objects and would disturb the quality of the screed.
External terraces and balconies
External floor heating (anti-frost protection) requires materials resistant to UV and frost. Standard plastic clips are usually made of PP or PE, which can withstand temperatures down to –30°C without becoming brittle. Fixing strips are equally suitable. The key difference is the waterproofing – it must be laid under the insulation and fixing elements must not pierce it. Details on waterproofing can be found in the article "Waterproofing film under floor heating – when and how to use it?"
Preparation for floor cooling
If the system is to be used for cooling in summer as well, fixing elements are not different – the same clips, strips, and bends are used. The change is in the floor composition (requirements for vapor barrier, condensation), which we write about in the article "Floor heating and cooling – what must the floor composition meet?"
Frequently asked questions (FAQ)
Can I skip clips if I have a system board with nubs?
On a system board with high nubs (nub height 20–25 mm), the pipe is held by the nub grid itself and clips are not necessary on straight sections. However, I recommend using them on bends as well, because the nubs do not prevent the pipe from rotating or shifting during concrete pouring. If you have a system board with low nubs (up to 10 mm), the pipe is not sufficiently secured and you should use clips or strips.
What is the correct spacing of clips on bends?
I recommend a maximum of 150–180 mm between clips on meander bends, with the first clip no more than 100 mm from the start of the bend. PEX pipe has strong elasticity and without sufficient fixing, the bend may open or shift. If you use fixing bends, it is sufficient to place 1 clip before and 1 after the bend.
What if a few clips fall out after the pipe is laid – do I have to re-fix everything?
A few missing clips before pouring is not a catastrophe, but they should be replaced. It is best to check the day after the pipe laying is completed – the pipe under tension gradually pushes against the clips and some that are poorly placed may fall out within a few hours. Just before the concrete crew arrives, walk the entire area and check that no pipe is protruding from the plane.
Can I use fixing strips for spiral (spiral) laying?
Yes, on straight sections running from the wall to the center of the room, strips work well. On bends in corners for spiral laying (90° bends), strips are not sufficient – use clips every 150 mm there. Overall, spiral laying is more fixing-intensive than meander, expect 20–30 % more clips.
Is it possible to attach fixing strips to a concrete slab (not to EPS)?
In some cases (e.g. renovation without EPS, direct mounting on an existing floor), EPS is not available and clip pins have nothing to grip into. In such a case, the solution is to use reinforcing meshes – the pipes are tied to the mesh with wire or plastic ties, which lies on spacers at the correct height. Strips and clips for standard EPS do not work in this scenario.
What is the effect of temperature during installation on the behavior of the pipe and fixing?
At temperatures below 10°C, PEX/PE-RT pipe is significantly stiffer – the elasticity in bends is stronger and clips may fall out more easily. I recommend increasing the number of clips by 20 % during installation in cold weather and allowing the pipe to acclimatize for at least an hour indoors (not outside) before installation. Fixing strips are more reliable in the cold than individual clips, because they secure the pipe at multiple points simultaneously.
Conclusion – good fixation is invisible, but essential
Fixing elements are often the material where savings are made during project calculation. The total cost of clips, rails and arches for 100 m² is a fraction of the cost of pipe or insulation. Despite this, it is precisely this "detail" that determines whether your floor heating system will function exactly as calculated – with even heat distribution, correct pipe depth in the screed, and long service life without mechanical stress. An experienced installer knows that good fixation = satisfied customer and no complaints after concreting. And this is a value that cannot be added later.
If you are considering the entire installation from the beginning, I recommend also reading other topics in the Knowledge Centre – for example, Floor heating installation step by step – from insulation to pouring, where fixation fits into the context of the entire process, or Maintenance and air venting of the floor heating system, so you know what to expect from your system after it is put into operation.
Do you have a question about this topic?
Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.