Installing Dry Underfloor Heating – Step-by-Step Guide for EPS 300 & Wood Fiber

A drywall underfloor heating system can be installed without wet screed, without weeks of drying times, and even by a single person. This manual shows you step-by-step how to correctly build a drywall system with dry screed – for the two most popular system panels: EPS 300 (expanded polystyrene rigid foam, 300 kPa) and Wood Fiber Acoustic. Both systems follow the same basic principle but differ in material, weight, impact sound behavior, and application area – all differences are clearly highlighted at the appropriate points.

1. System Overview: EPS 300 vs. Wood Fiber Comparison

Both systems work on the same principle: The system panel accommodates the heating pipe, aluminum heat spreader plates distribute the heat evenly across the surface, and a dry screed load distribution layer (gypsum fiber boards) forms the finish.

When to choose EPS 300: If the substrate is level and load-bearing, there are no special sound insulation requirements, and a system that is as lightweight and cost-effective as possible is desired.

When to choose wood fiber: If the timber beam ceiling is loaded, impact sound protection is to be integrated, or ecological building materials are preferred. The wood fiber board regulates moisture and is particularly suitable for old building ceilings.

2. Material Requirements & Tools

Materials (per 1 m² heated area – approximate values)

• System panels EPS 300 or wood fiber, 25 mm: 1.0 m²
• Heat spreader plates Ω-profile 16 mm: approx. 4–5 pieces à 0.75 m (with 150 mm laying spacing)
• Heating pipe PERT-AL-PERT 16×2 mm: approx. 6–8 m (depending on laying spacing)
• Edge insulation strips: Length = room circumference + 10% allowance
• Thermal insulation (mandatory according to DIN EN 1264-4, see step 3): depending on the substrate
• PE film as a slip layer: 1 m² (min. 0.2 mm thick)
• Dry screed panels (gypsum fiber 2×12.5 mm, e.g., Fermacell 2E22): 1.0 m²
• Screed adhesive for tongue-and-groove bonding: approx. 60–70 ml/m²
• Drywall screws 3.9×22 mm: approx. 10 pieces/m²

Tools

• Utility knife or circular saw (with dust extraction) for panel cutting
• Hot cutting device or router for individual pipe routing
• Pipe unroller / uncoiling device
• Pressure gauge for leak testing
• Rubber hammer, angle, straightedge (2 m)
• Screwdriver (for dry screed assembly)
• Glue gun or dosing bottle for screed adhesive
• Tape measure, chalk line

3. Step 1 – Check & Prepare Substrate

A level, dry, and load-bearing substrate is the basic prerequisite for a functional drywall system. Difference from wet screed: While screed compensates for unevenness itself, the EPS or wood fiber board lies directly on top – cavities underneath lead to pressure points and, in the worst case, to cracks in the dry screed.

Requirements according to DIN 18202 (Table 3/4)

The flatness of the substrate must comply with the following deviations according to DIN 18202:

Inspection: Use a 2-m straightedge to check the surface diagonally and across. Wherever the gap is larger than the table values, compensation must be made.

Compensation for unevenness

• Up to 5 mm: compensate for localized unevenness with suitable filler
• 5–20 mm area-wide: apply self-leveling compound (e.g., leveling screed, leveling compound)
• Over 20 mm / height displacement due to pipes: apply leveling screed or bound screed, then level with leveling compound

Specifics per subfloor type

Concrete ceiling / solid ceiling: Sweep the subfloor, remove mortar residues. Check for residual moisture (CM measurement) – if values are >2% CM, plan a PE film as a vapor barrier. Between two heated floors, the PE film should generally be omitted; it is mandatory for ground-contacting floors or residual moisture.

Timber beam ceiling: Firmly screw down all planks and boards – no springiness or creaking is permissible. Close joints and cracks with filler, then sand and vacuum. The subfloor must be ventilated. For wood, a deep primer is recommended before gluing the EPS board to reduce absorbency.

Important: Completely remove loose components, dust, grease, and release agents. Inform subsequent trades about the installed underfloor heating so that no damage occurs. Protect the finished laid surface until handover.

4. Step 2 – Install edge insulation strips

Before any insulation layer or system board is laid, the edge insulation strips are installed. They are not a minor detail – they decouple the entire floor structure from the walls, preventing sound bridges and cracks due to thermal expansion.

Requirements according to DIN EN 1264-4:

• Minimum thickness: 5 mm (recommended in practice: 8 mm)
• Height: from the load-bearing subfloor to the top edge of the finished floor covering
• Material: Polyethylene foam or mineral wool; for fire protection requirements, the edge insulation strip must consist of mineral wool with a melting point ≥1000 °C

Installation: Glue or staple edge insulation strips along all walls, supports, stairs, door frames, and fixed building components. The film apron faces into the room. Cut off the protruding part only after laying the floor covering – never before.

Expansion joints: For room lengths exceeding 8 m or areas exceeding 40 m², field boundaries with elastic sealant must be planned. This applies in particular to tiled floors. Coordinate the location of the joints with the floor layer.

5. Step 3 – Laying the insulation layer (in accordance with DIN EN 1264-4)

This step is often underestimated – or even completely omitted. This is a mistake: DIN EN 1264-4 mandates minimum thermal resistance (R-values) for the insulation layer. While EPS 300 and wood fiber provide insulation themselves, they are often not sufficient on their own in most situations.

Why additional insulation is necessary

EPS 300 (25 mm): Own R-value (at λ = 0.032) ≈ 0.78 m²K/W — barely meets the minimum requirement of 0.75 m²K/W (heated below).

Wood fiber (25 mm): Own R-value ≈ 0.63 m²K/W — not sufficient for any subfloor type alone. Always plan for additional insulation.

Mandatory values per subfloor type (DIN EN 1264-4, Table 1)

Formula: Required insulation thickness d = R × λ. Example: R = 1.25 m²K/W × λ = 0.035 W/mK = 0.044 m → 44 mm EPS 035.

Execution of the insulation layer

• Lay insulation boards fully and without voids – no gaps or tilting
• Offset joints (staggered laying), never join continuously in one strip
• For 2-layer installation (e.g., for R = 2.00 m²K/W): offset layers by half a board length
• Insulation must be pressure-stable – EPS DEO ≥100 kPa (residential construction), ≥150 kPa for higher loads
• For ground-contacting floors: prefer XPS (more moisture resistant than EPS)

Timber beam ceiling – special feature: Prefer wood fiber as insulation. It also improves impact sound insulation and regulates moisture. For leveling screed in the beam fields: insert a load distribution board (10 mm gypsum fiber, loose) between the screed and the system board.

Wood fiber is vapor-permeable and, depending on the product, can absorb a significant amount of moisture without immediately losing its insulating effect. This creates a capillary-active structure that can tolerate condensation and short-term moisture peaks better than many dense insulation materials.

6. Step 4 – Moisture protection (PE film)

The PE film plays two different roles in the installation – it is important to understand this:

As a vapor barrier (under the insulation): For ground-contacting floors (ground floor without basement, basement floor slab), the waterproofing must be carried out in accordance with DIN 18533. A simple PE film is only sufficient here as a supplementary measure; the actual waterproofing is done with a bitumen membrane, liquid film, or equivalent waterproofing. If there is no external waterproofing: first retrofit, then install underfloor heating.

As a sliding layer / separation layer (over the system board): A PE film is laid as a separation layer between the system board and the dry screed boards. It prevents the dry screed from sticking to the system board and allows for thermal expansion of the structure without tension. Overlap sheets by at least 20 cm (standard requirement min. 8 cm), pull up laterally against the edge insulation strips.

Minimum thickness: 0.2 mm in practice (standard specifies 0.15 mm as minimum).

7. Step 5 – Laying & gluing system boards

This is the core step, which differs slightly for EPS 300 and wood fiber.

Planning before laying

Before the first adhesive: dry-lay the boards and mentally plan the pipe routing. Sketch areas with tight radii (doorways, heating manifold) in advance. Make cuts with a utility knife or circular saw – save offcuts for smaller areas.

Bonding to mineral substrates (concrete, screed)

1. Apply adhesive (suitable flexible adhesive) fully to the subfloor with a notched trowel (8 mm teeth)
2. Place the board with a slight sliding motion and press down with body weight
3. Ensure full contact – no voids under the board

For EPS 300: Standard flexible adhesive is sufficient; EPS boards are dimensionally stable and easy to work with.

For wood fiber: Use water-resistant flexible adhesive – wood fiber is more sensitive to moisture ingress. Notching 6–8 mm.

Bonding to wood substrates

Wood substrates absorb adhesive quickly – therefore, apply deep primer beforehand and allow it to penetrate. Use water-resistant, flexible adhesive (e.g., MS polymer adhesive). Notching 6 mm. Wood fiber boards are the better choice on wood – they are vapor-permeable and moisture-regulating; EPS is vapor-tight.

Laying direction & joint offset

Lay boards in a staggered pattern (joint offset at least half a board length). Align the first row with a chalk line. Keep joints between boards as tight as possible – no adhesive in the pipe routing channels. Offcuts can be reused, provided the pipe routings are correct.

Caution: The MC Therm dry construction system boards are not intended as a statically load-bearing layer. Load transfer, thermal and impact sound insulation, and moisture protection must be ensured by the substructure.

8. Step 6 – Insert heat spreader plates

The heat distribution plates made of galvanized sheet steel or aluminum are the core of heat transfer in the dry construction system. They hold the heating pipe in their Ω-shaped recess and distribute the heat laterally into the system plate – and from there into the dry screed and the floor covering.

Installation: Press the heat distribution plate into the guide groove of the system plate until it clicks into place. Ensure an even spacing between the plates – a gap of 5 mm between adjacent plates is recommended. Do not insert any plates at an angle or with a gap.

Deflection areas: In the bends of the pipe run (180° deflection), additional heat distribution plates can be placed as a cover to ensure even heat distribution there and to create a walkable surface.

If the pipe run needs to be changed: Cut and fold back the aluminum cover, then create a new pipe guide with a hot cutting device (approx. 17 mm deep). The pipe may protrude a maximum of 1 mm above the plate surface.

9. Step 7 – Laying & Connecting the Heating Pipe

Heating Pipe Selection

A PERT-AL-PERT composite pipe (polyethylene-aluminum composite pipe) is recommended. It is absolutely oxygen-tight, dimensionally stable, retains its shape, and is approved for drinking water installations. For 16-mm systems: 16×2 mm.

Alternatively: PERT/EVOH/PERT – particularly flexible and good for tight radii.

Laying Process

• Ideally, lay the pipe from a dispenser to avoid tension and kinks.
• Guide the pipe from the manifold towards the heated area and press it into the heat distribution plates.
• In the 180° bends, do not exceed the bending radius (observe manufacturer's specifications – typically ≥5× pipe diameter).
• For 180° bends or if the pipe jumps out of its guide: Cut out the EPS plate locally, fix the pipe with a mounting clip, fill the recess with flexible adhesive.

Heating Circuit Lengths & Manifold Connection

• Recommended maximum heating circuit length: 90-100 m per heating circuit (for 16-mm pipe), correspondingly shorter for 14-mm pipe.
• Connection to the heating circuit manifold via Eurocone screw connections.
• Set flow rates using the flow meters on the manifold.
• Label and document heating circuits (room assignment, length).

Important Notes

Inform subsequent trades about the location of the heating pipes. Protect the area until the floor covering is installed – especially from screws or sharp objects.

10. Step 8 – Leak Test

Before covering with the PE film and dry screed boards, a leak test must be carried out. It is a prerequisite for warranty claims and protects against hidden leaks.

Procedure:

1. Fill the heating pipe with water and bleed it.
2. Increase test pressure to 1.3 times the operating pressure (min. 6 bar).
3. Maintain pressure for 24 hours.
4. Document pressure drop and visual inspection.

If the pressure remains stable and no wet spots are visible: test passed. Keep the protocol (for warranty and as proof to the heating installer).

The system remains under operating pressure throughout the entire subsequent installation – this way, damage from subsequent work is immediately detected.

11. Step 9 – Laying PE separating foil & dry screed

PE separating foil

The separating foil (min. 0.2 mm) is laid completely over the system plates and heating pipes. Overlap the sheets by at least 20 cm, pulling them up at the sides to the edge insulation strip. The foil serves as a sliding layer – it thermally decouples the dry screed and prevents it from sticking to the system plates.

Dry Screed – Selection

Gypsum fiber screed elements (e.g., Fermacell 2E22) are recommended: two 12.5 mm gypsum fiber boards glued together with a stepped rebate. Dimensions: 1500×500 mm. Other options: 2×10 mm (lower construction height) or cement-bound boards for wet rooms.

Installation

1. Lay elements in a staggered pattern – minimum joint offset of 200 mm.
2. Joints of the dry screed boards must not coincide with joints of the system boards.
3. In the stepped rebate area, apply screed adhesive (e.g., Fermacell greenline) evenly with the enclosed dosing nozzle.
4. Push boards together quickly and press down.
5. Screw with quick-build screws 3.9×22 mm (approx. 10 pieces/m²) – screws must not hit heating pipes; mark pipe position beforehand.
6. Remove any excess adhesive immediately.

Caution when screwing: Mark the heating pipe position on the plate surface before screwing. Never place screws in the area of the pipe guides.

Walkability

After complete curing of the adhesive (24–36 hours at 20 °C, 50% relative humidity), the dry screed is walkable. Full load-bearing capacity is reached after approx. 72 hours.

Edge areas & expansion joints

• Never lay dry screed boards right up to the wall – the edge insulation strip must remain free.
• For room lengths over 8 m or areas over 40 m²: Provide field boundaries with elastic sealant.
• Always execute connection joints to walls, pipe penetrations, and door frames elastically.

12. Step 10 – Laying Floor Covering

The dry construction system can be combined with almost all floor coverings – provided that the covering is approved for use with underfloor heating (check manufacturer's specifications).

Initial Start-up

The initial start-up should be carried out gradually – no shock heating:

1. Set flow temperature to 25 °C, hold for 3 days.
2. Then increase by +5 °C per day until operating temperature is reached.
3. Maximum recommended flow temperature: 55 °C
4. Document heating protocol according to DIN EN 1264 (mandatory for warranty).

13. Construction Heights & System Weights at a Glance

EPS 300 – Apartment Partition Ceiling Construction (heated room below)

Wood Fibre – Timber Beam Ceiling Construction (heated room below)

For comparison: A wet screed system uses 5–10 cm of screed alone, with a weight of 100–120 kg/m². The dry construction system is thus 3–5 times lighter – a crucial advantage for wooden beam ceilings and old building ceilings with limited load-bearing capacity.

14. Common mistakes & how to avoid them {#14-häufige-fehler}

Mistake 1: Insulation layer omitted or too thin The most common cause of inefficient operation. Without sufficient insulation, heat flows downwards instead of into the room. Always check DIN EN 1264-4 table 1 and adhere to the target R-value for each substrate.

Mistake 2: Unevenness in the subfloor not compensated EPS and wood fiber boards do not compensate for unevenness. Voids under the board lead to cracks in the dry screed under load. Measure the subfloor with a straightedge and level it before installation.

Mistake 3: Heat conducting plates forgotten or incorrectly used Without heat conducting plates, the heating pipe only distributes heat pointwise – warm-cold stripes appear in the floor, which can be felt. Each pipe must be completely seated in an Ω-plate.

Mistake 4: Screws put through heating pipes Happens when screwing the dry screed. Always mark the pipe position on the board surface before screwing.

Mistake 5: No leak test before covering Leaks discovered only after the dry screed has been laid mean complete removal. A leak test is mandatory – even if the pipes are still accessible visually.

Mistake 6: Cutting edge insulation strips too early The strip must remain until after the floor covering has been laid. If it is removed beforehand, sound bridges and cracks at the wall connections will occur.

Mistake 7: Shock heating during initial commissioning Leads to stress cracks in the dry screed. Always heat gradually (25 °C, +5 °C/day).

15. Conclusion

A dry construction underfloor heating with dry screed is not rocket science – if you follow the right steps in the right order. The most common mistake is omitting the insulation layer or an insufficiently prepared subfloor. Both omissions only become apparent during operation: as inefficient heating, cold zones, or cracks in the covering.

EPS 300 is the all-purpose, lightweight standard system for most applications. Wood fiber is the ecological system with integrated impact sound insulation – ideal for wooden beam ceilings and old buildings. Both systems can be installed without wet screed and without long waiting times – and are perfectly coordinated in conjunction with the MC Therm dry construction complete set .

All information corresponds to the state of the art and refers to DIN EN 1264-4:2021, DIN 18202, DIN 18560, and the current manufacturer specifications of the products used. For planning-relevant decisions (insulation thicknesses, heating load, hydraulic balancing), we recommend involving a specialist planner.

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