System Board vs. Grid Foil – What’s Better for Your Subfloor?
System board vs. grid film – what is better for your subfloor?
When underfloor heating work begins, one of the first practical questions that every installer and DIY builder asks is: how do I actually secure the pipe? The two most common solutions on the Slovak and Czech markets are the system (foam) board with an integrated grid and a separate grid film combined with fixing elements. Both solutions work – but they differ significantly in terms of which subfloor, project and budget they are more suitable for. In the following text, I will examine both options in detail, including real numbers, practical scenarios and common mistakes I have seen on many projects.
Why the choice of fixing layer matters
The fixing layer is not just some kind of "pipe carrier". It is part of the overall floor construction, which affects thermal resistance, the height of the construction, acoustic properties and the speed and quality of installation. A poorly chosen layer can mean that the pipe floats slightly after being poured into concrete, air pockets form, anhydrite does not flow under the pipes or the insulation unnecessarily thickens by centimeters that no one planned. In an apartment on the 4th floor, every extra centimeter of height is a problem – doors, threshold strips, tiles, furniture, everything has to be adjusted.
At the same time, the choice of fixing layer is related to the choice of insulation below it. If you are interested in how to correctly dimension the insulation board itself, I recommend looking at the article How to choose an insulation board for underfloor heating – thickness, material and requirements, where the Lambda values, required thicknesses and differences between EPS, PIR and mineral wool are discussed in detail.
System (foam) board – principle and advantages
The system board is a laminated or pressed EPS board with characteristic nubs (protrusions) that form an accurate grid pattern. The pipe is simply inserted between the nubs – no screwing, no cutting of strips, no measuring of distances. The nubs are mostly designed for pipe Ø14–20 mm, most commonly 16 and 17 mm. The distance between the nubs corresponds to modules of 50 mm or 75 mm, so the pipe can be laid at distances of 50, 100, 150, 200, 250, 300 mm and so on, always in multiples of the basic module.
In terms of installation, the system board is the fastest option. An experienced pair of installers can handle 100–150 m² in one working day in a system board, including cutting, assembling and laying the pipe. The boards are mostly half-tongued on the edges, so they fit into each other without gaps and no thermal bridges are created.
The thermal insulation value of system boards depends on their thickness – they are typically available in variants of 30 mm (lambda ≈ 0.035–0.040 W/m·K), which corresponds to an insulation resistance of R ≈ 0.75–0.86 m²·K/W, or 50 mm (R ≈ 1.25–1.43 m²·K/W). This is usually not enough for contact floors above unheated spaces, where the EN 1264 standard and our STN require R ≥ 0.75 m²·K/W and sometimes more. On contact floors, an additional layer of rigid thermal insulation must be added under the system board.
Where the system board really shines
From practice, I know that the system board is ideal in these situations:
- Apartment renovation in a panel building – interfloor slabs have a different thermal balance than ground-level floors, the insulation does not have to be thick, so it is possible to get by with a 30 mm system board and save height
- Smaller areas (up to about 80 m²) – the cost of measuring, cutting and fixing the film is not worth it, the system board is more convenient
- Situations where the installer values speed – in the construction of several apartment units, time saving is a real economic argument
- Customers who install themselves – with a system board, it is hard to make a major mistake in the spacing or fixing of the pipe
Grid foil – principle and advantages
The separation grid foil is a thin (usually 0.1 mm) polyethylene foil with a printed or embossed grid pattern in modules of 50 × 50 mm or 50 × 100 mm, which serves as a guide when laying the pipe. The foil itself does not form insulation – it is placed directly on top of rigid thermal insulation (EPS, PIR, PUR boards). The pipe must be fixed to the foil using external fixing elements.
At Atria.sk you can find for example separation foil IVAR with grid – 0.1 × 1030 mm; AL – 50 m², which has an aluminum layer on the surface improving radiation reflection and also serves as a separation layer against moisture from the screed. Foil strips are joined using metallic tape for joining foils – 55 mm × 50 m, which ensures an airtight and mechanically strong bond between the strips.
The pipe is fixed on the foil either by:
- fixing strips – for example pipe fixing strip 16–18 mm; 1 m / 100 pcs, which is mechanically connected to the EPS board under the foil,
- plastic clips – for example pipe fixing clip – 50 mm; straight, which you push through the foil into the EPS,
- PEX fixing arches – for example PEX pipe fixing arch 16–18 mm, suitable especially for arches and pipe direction changes.
The advantage of the foil solution is the flexibility in choosing the insulation. The investor or designer can choose exactly the thickness and type of insulation that the project prescribes, and the grid foil simply spreads on top regardless of whether it is 20 mm PIR or 150 mm EPS 100 underneath. This is a key argument for projects with demanding thermal insulation requirements.
Where the grid foil excels
- Large areas (100 m² and more) – the price per m² is significantly lower than with a system board; in large halls, commercial spaces or single-family homes with full-floor heating, the difference per m² multiplies
- Floors above unheated spaces and above ground level – the possibility to use thick insulation without compromises
- Combination with PIR insulation – PIR boards have very low lambda (0.022–0.026 W/m·K), but they do not have a surface suitable for directly inserting nops; the foil covers them and fixing elements secure the pipe
- Projects with non-standard pipe spacing – the grid pattern of the foil allows any spacing according to the project (e.g. 75 mm for cooling applications or 250 mm in less exposed zones)
- Combination with wet process (cement screed) – foil with welded strips and an aluminum surface also performs well as a vapor barrier and separation layer
Direct comparison of parameters and price
Let's look at specific numbers. In the Slovak market, these are the approximate values (excluding VAT, for the period 2024–2025):
| Parameter | System nopped board | Grid foil + insulation |
|---|---|---|
| Material cost (layer itself) | 5–12 €/m² | 0.80–1.50 €/m² (foil) + insulation 2–8 €/m² |
| Total layer thickness | 30–65 mm (insulation + nops) | 20–200+ mm (any) |
| Installation speed (100 m²) | 1 day (pair) | 1–1.5 days (pair) |
| Need for external fixation | No (nops fix themselves) | Yes (clips, strips, arches) |
| Flexibility of spacing | Modular (multiples of 50 mm) | Any (according to foil grid) |
| Suitability for thick insulation | Limited (max. 60 mm common) | Unlimited |
| Separation / vapor barrier | Partial (depends on surface) | Yes (AL foil) |
| Typical use | Apartments, renovations, small areas | Homes above ground level, large areas, commerce |
Influence of the base on the choice of solution
This is the core of the whole matter. It is not just a matter of preference – the base literally decides which solution is technically correct.
Intermediate floor slab (concrete, Filigran, Spiroll)
This is the most common case in residential construction and renovations. The floor is essentially flat and achieves sufficient load-bearing capacity. Thermal insulation requirements are modest – an intermediate floor slab does not need to separate a heated space from an unheated one, it only needs to meet acoustic requirements and prevent heat loss downwards. Usually, insulation of 30–50 mm is sufficient. In this case, a 30 mm (or 35 mm with an acoustic layer) system foam board is an ideal choice – it combines insulation, grid and fixing in one element, is quick to install and saves 1–2 cm in the construction height compared to a solution with separate insulation + foil.
Ground floor (foundation slab, basement)
This situation is completely different. Standards and physics require significantly higher thermal insulation – typically a minimum of R ≥ 1.25 m²·K/W, which corresponds to a thickness of 44 mm with EPS 035, but in practice, 60–100 mm or more is designed. A system board with R ≈ 0.75–0.86 m²·K/W at 30 mm is not sufficient here. The solution is either a combination of 60 mm rigid EPS + 30 mm system board (total thickness 90 mm, which is a lot), or a cleaner solution: 80–120 mm EPS 100 + separation foil with a grid + fixing clips. The result is thermally correct and the thickness is smaller.
If groundwater or moisture occurs on the ground, a foil with an aluminum layer also serves as a vapor barrier. More on this can be found in the article Separation foil under floor heating – when and how to use it?
Floor above an unheated space (garage, cellar)
This base is the most thermally demanding, as the temperature difference can be 20–30°C in winter. Standards ENB and STN 730540 prescribe Uf ≤ 0.24–0.15 W/(m²·K) for such constructions, depending on the building's energy class. Achieving these values requires insulation with R ≥ 3.5–5.0 m²·K/W, i.e., EPS thickness in the range of 120–180 mm, or PIR thickness of 80–120 mm. In this case, a grid foil is practically the only reasonable choice – above 60 mm EPS, system boards are exceptional and expensive.
Old wooden beam-supported floor (during renovation)
This is a specific case where neither solution is completely ideal in a wet process. Beam ceilings have limited load-bearing capacity (usually 200–300 kg/m²) and cement screed alone weighs 100–130 kg/m² at a thickness of 60 mm. A system board made of light EPS can help here – pipe fixing does not require drilling or screwing into the wooden structure. Alternatively, a dry installation (without screed) is used in such cases, where a foil solution is not suitable. More about this scenario can be found in the article Installation of floor heating step by step – from insulation to pouring.
Combination of both solutions – when it makes sense
In practice, a hybrid solution is occasionally the most optimal. For example, in a family house where the ground floor is above an unheated garage and the upper floor is an intermediate floor slab: thick insulation + grid foil is used on the ground floor, and a system board on the upper floor. Material logistics are a bit more complex, but each floor gets the correct technical solution without compromises.
Another practical case: the investor wanted a 75 mm pipe spacing (cooling) in the living room and 100 mm (heating) in the bathroom. A system board with a 50 mm module allows 50, 100, 150 mm – but not 75 mm. The solution was a separation foil with a 50 mm grid, where the installer simply inserted the pipe every 1.5 cells. This is a typical flexibility that a system board cannot offer. More on pipe spacing sizing can be found in the article What pipe diameter and spacing do I need for floor heating?
Installation details that are often forgotten
System board – critical details
The system board must be laid with the correct orientation of the foam cells – if you want the pipe in a certain direction, the cells must be aligned with the planned spacing. If the board is incorrectly rotated, unnecessary gaps are created where the pipe does not hold. Boards must be precisely cut at building edges and partitions – the remaining EPS under the plaster or tile without a screed above can slide under load.
The edge expansion strip must be placed around the entire room perimeter before laying the boards, not after. If this is forgotten and the board is placed against the wall, the screed expansion will have nowhere to go and cracks will form. This type of error is among the most common – more in the article Common mistakes in pipe laying for floor heating and how to avoid them.
Mesh foil – critical details
Stripes of foil must overlap at least 50–100 mm and be joined with a metallic tape along the entire length of the joint – not just with local pieces. Insufficient joining of foils will allow moisture from anhydrite or cement to penetrate through the gaps into the insulation, which reduces its thermal insulation properties. With aluminum foils, the adhesion of the metallic tape is crucial – the tape must be specially designed for the AL surface, ordinary mounting tape will not remain stuck for a long time.
Fixing clips must be driven through the foil into the EPS sufficiently deep – at least 25–30 mm. A clip that only lightly perforates the foil will hold during pipe laying, but when the system is filled with pipes and pressure tested, the pipe may loosen and float upwards during anhydrite pouring. It is excellent to alternate clips every meter of pipe or according to the manufacturer's instructions for fixing elements.
For curves and changes in direction, special fixing curves are recommended (e.g., PEX pipe fixing curve for 16–18 mm), which give the pipe the correct curved shape without unnecessary tension. Direct clips in a curve are not sufficient – the pipe will try to straighten under water pressure and the curve may shift.
Cooling – special requirements for the fixing layer
If the system is to serve also for cooling (reversible heat pump), additional requirements arise for the entire construction during cooling. The pipe is cold, and moisture from the concrete or surroundings condenses on the floor surface. In this case, a foil with an aluminum surface performs the function of a vapor barrier, preventing moisture from the soft insulation from moving upwards to the condensing pipe. A system board usually does not fulfill this function – its EPS is diffusion open and during cooling, moisture can enter from above and below. Therefore, a foil solution is advantageous in cooling projects. Further details can be found in the article Floor heating and cooling – what must the floor composition meet?
Economic calculation for a typical family house (150 m²)
To be specific, I will show an approximate calculation for a family house with 150 m² of heated area above an unheated garage (required thickness of EPS 100S insulation: 100 mm):
| Item | System board (30 mm EPS + 30 mm foam) | Foil + EPS 100 mm |
|---|---|---|
| Insulation (material) | 30 mm EPS: ~1.50 €/m² × 150 = 225 € | 100 mm EPS: ~5.00 €/m² × 150 = 750 € |
| Fixing layer | Foam board 30 mm: ~8 €/m² × 150 = 1 200 € | Foil: ~1.20 €/m² × 150 = 180 € |
| Fixing clips/straps | — | ~0.50 €/m² × 150 = 75 € |
| Sealing tape | — | ~30 € |
| TOTAL | 1 425 € | 1 035 € |
| Thickness of the entire composition | ~90 mm (insufficient insulation!) | ~105 mm (correct insulation) |
| Thermal insulation resistance R | ~1.7 m²·K/W (only 0.75 without additional insulation) | ~2.8 m²·K/W |
From the calculation, it is clear that for a floor above a garage, the foil solution is cheaper and technically more correct. A system board would have to be combined with additional insulation, which would increase the cost and thickness even further.
Most frequently asked questions (FAQ)
Can I use a system board directly on a bare concrete slab without additional insulation?
Technically yes, but thermally only if calculations of the thermal balance confirm it. A 30 mm system board with lambda 0.038 W/m·K provides R ≈ 0.79 m²·K/W. This may be sufficient for interfloor slabs between two heated floors, but it is not enough for floors over ground or unheated spaces. Never proceed without assessment by a project designer or technical advisor.
Can a separating mesh foil be used without fixing clips, for example, if I am in a time crunch?
Not recommended. The foil alone does not hold the pipe – it is only 0.1 mm thick. Without clips, the pipe will float up during anhydrite pouring and the spacing and routing will be ruined. A pressure test before tiling will only reveal tightness, not the position of the pipe. Clips and strips are cheap and their installation takes minutes per meter – skipping them is a gamble with the entire system.
What is the lifespan of a system EPS board in a floor composition? Won't it be damaged over time?
EPS is a long-term stable material. When properly placed, without direct contact with solvents and without long-term wetting, EPS boards will last the same decades as the entire building. Problems arise only under bad conditions: when water penetrates from above (pipe leak, poor screed) or from below (groundwater). Therefore, waterproofing and proper sealing of the foil with metallic tape are important. More in the article Waterproof foil under floor heating – when and how to use it?
System board or foil – which is better for anhydrite vs. cement screed?
Both fixing systems are compatible with anhydrite and cement screed. The difference is that anhydrite is more fluid and can get under the pipe without air pockets, which reduces the requirements for fixing – clips spaced 50 cm apart are sufficient. With cement screed, which is denser and manually applied, a firmer fixing of the pipe is needed, otherwise it will shift during troweling. A system board is more advantageous here, as the feet physically block the pipe.
Can I combine a system board from one manufacturer and a foil from another?
Yes, they are not system-bound products. A mesh foil is a standardized aid, fixing clips are standardized dimensions for Ø16 and Ø20 mm. There is no mandatory system binding. It is important to ensure compatibility of clip diameter with pipe diameter and proper joining of foils with the appropriate metallic tape.
What if I have an uneven base? Can I level it with a system board or foil?
Neither solution is intended for leveling the base. A system EPS board flows under load – if the unevenness is greater than 5 mm over a 2 m straightedge, the base must first be leveled with self-leveling screed or dry underlayment. Foil is even less tolerant – on an uneven base, the insulation under it breaks at the corners and the pipe does not stand evenly. The rule for base flatness: maximum deviation ±5 mm over 2 m. Checking with a Rot-matic or 2 m straightedge is mandatory before starting work.
Conclusion – what to take away from this comparison
A system foam board is an elegant, fast, and easy-to-install solution for apartments, reconstruction of interfloor slabs, and smaller areas where insulation does not need to be thick. It makes sense when you value speed and simplicity, the pipe spacing corresponds to 50 mm modules, and the overall insulation thickness of up to 50–60 mm is sufficient.
Separating foil with a grid combined with rigid insulation and external fixing elements (trims, clips, arches) is a technically more appropriate choice for floors above unheated spaces, above ground level, in cooling projects, and for large areas where the price difference per m² multiplies into significant sums. Moreover, it gives the designer and installer full freedom in choosing the insulation – thickness, material and thermal performance.
In both cases, the common denominator is the quality of installation: correct expansion joints, secure pipe fixing, sealed foil joints, and inspection before covering. Technical details and a step-by-step procedure can be found in the article Underfloor heating installation step by step – from insulation to pouring and in the article Fixing underfloor heating pipes – clips, trims and arches, where it is in detail discussed when to use which fixing element and how to properly install them.
Do you have a question on this topic?
Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.