Top floor ceiling — termPIR® AL (section)

Function of the junction

Top floor ceiling insulation from above (from the attic side) = the simplest and cheapest alternative to roof slope insulation. Used when:

• The attic is unused (storage or drying space only) — there is no point in insulating the roof if the space beneath it will not be heated.
• Renovation of an older building — the existing roof covering is preserved without intervention.
• Limited budget — a horizontal ceiling has a smaller area (and cost) than all roof slopes combined.

Build-up:

1. PUR adhesive (item 05) — Ceresit CT 84 or PCI Pecimörtel, full-surface bonding.
2. termPIR® AL board (item 02) — directly onto the reinforced concrete; 12–20 cm thick (for WT 2021 attic ceiling requirement U ≤ 0.15).
3. Aluminium tape (item 03) — on all board joints.
4. OSB (item 04) on top — allows walking on the attic without damaging the termPIR®.

Critical installation aspects

• PUR adhesive (item 05) — Ceresit CT 84 or PCI Pecimörtel — full-surface application (not spot-bonding); bonding to the reinforced concrete surface without prior priming (cleaning + vacuuming only).
• Aluminium tape (item 03) — crucial! Applied after the boards are laid (per original note); minimum width 75 mm, on all joints; maintains the vapour-tightness of the insulation layer.
• OSB (item 04) — minimum 18 mm thick (for a 200 kg/m² load — typical attic load); fixed with screws to timber battens inserted into the AL boards.
• Battens beneath OSB — impregnated timber 50×60 mm, spaced 60 cm; pressed into cut-outs in the AL board; fixed with screws to the substrate through the board (long screw + plate washer + gasket).
• OSB expansion gap — 3 mm between boards; fixed with screws NOT to the AL but to the battens.
• Attic access — usually a hatch with a ladder; the hatch must be insulated (termPIR® AL 50 mm on the lid + EPDM gasket around the perimeter); without this, the air bridge = 5–10% loss in ceiling insulation efficiency.

Documentation

Technical Catalogue termPIR® — Residential Buildings (Gór-Stal 2022), page 63 — Ceilings and floors, top floor ceiling, section through the ceiling. Scale 1:10.

Components in this junction