Ceiling Detail — Under-Rafter Roof W2 (termPIR® AL GK Under Collar Ties)

Junction function

Attic ceiling in W2 = a simplified version of the W1 ceiling (page 24). Instead of a termPIR® AL layer between collar ties + a separate AL board under the ties + a separate plasterboard, we use:

1. termPIR® AL between collar ties (item 04) — unchanged vs W1.
2. termPIR® AL GK under collar ties (item 05) — a single composite layer = insulation + plasterboard facing.

Key advantage: fewer layers, fewer joints, less room for installation error.

This junction is used when the attic is to be finished in white / colour and treated as a usable storage attic (e.g. lumber room, laundry). For a fully habitable attic (bedroom), revert to W1 with thicker insulation.

Critical installation aspects

• termPIR® AL GK board (item 05) — dimensions 1200×2400 mm, shorter edge parallel to the collar ties; fastened through the substructure battens (item 03) to the collar ties.
• Screws (item 06) — long self-drilling, through batten + AL GK board → embedment in timber min. 60 mm.
• Joints filled with tape and gypsum compound directly on the factory plasterboard facing of the AL GK — no priming required.
• OSB (item 01) — from above, on the collar ties; with a 3 mm expansion gap between boards.
• No PE vapour barrier — in W2 the AL GK board already has a vapour-tight aluminium facing on the cold side. For humid rooms (bathroom under sloped ceilings) → add a PE foil as in W1.
• No technological gap between insulation and plasterboard — the composite eliminates this void; saving 2–4 cm of room height.

Used in the pitched roof — termPIR® under-rafter system.

Documentation

Technical Catalogue termPIR® — Residential Buildings (Gór-Stal 2022), page 28 — Pitched roof W II, ceiling detail. Scale 1:10.

Components in this junction