Heated floor on ground (termPIR® AL + reflector)

Junction function

Underfloor heating = standard for modern single-family homes with a heat pump (low supply temperature 30-40°C, ideally matched to underfloor heating). Requires additional layers vs standard floor (p. 66):

1. Aluminium reflector (item 04) above termPIR® — key element of efficiency; redirects thermal radiation upwards instead of into the insulation. Increases heating efficiency by 8-12%.
2. Heating screed (item 02) — with embedded PE-X / PE-RT pipes; thickness min. 6 cm above pipes (for proper heat distribution).
3. Heating pipes — typically PE-X 16/2 mm at 10-20 cm spacing; layout per project with the manufacturer.

Critical installation aspects

• Aluminium reflector (item 04) — NOT ordinary PE foil; special aluminium foil 300–450 g/m²; “grid” pattern for fixing pipes (e.g. Pure Layfix / Schluter Ditra-Heat system); key for underfloor heating efficiency.
• Without aluminium reflector — ~12% of heat goes downwards (into the insulation); with reflector >95% of heat goes upwards into the room.
• Heating screed (item 02) — min. 6 cm above pipes for even heat distribution; reinforced with polypropylene fibres; no steel reinforcement (extensive cracking during heating).
• Heating pipes — embedded in the screed; spacing 10 cm along the edge zone (at windows, in the bathroom), 15-20 cm in the room field. “Snail” or “meander” spiral patterns.
• termPIR® AL (item 03) — typically 15-20 cm thick (vs 10-15 for standard floor); underfloor heating requires better downward insulation (screed is 30-40°C, ground 10°C → large temperature difference = greater losses without insulation).
• Perimeter expansion strip — 10 mm polystyrene around the entire perimeter; for underfloor heating, double the thickness to 20 mm due to greater thermal expansion of the screed.
• Floor finish (item 01) — ceramic tiles are best (high thermal conductivity λ ≈ 1.2); wooden panels acceptable but with a “for underfloor heating” certificate; solid parquet = not recommended (will crack over time from cyclic heating/cooling).

Documentation

Technical Catalogue termPIR® — Residential Buildings (Gór-Stal 2022), page 65 — Floors and slabs, detail of slab insulation and heated floor on ground. Scale 1:10.

Components in this junction