Ceiling detail — over-rafter roof (termPIR® AL between collar ties)

Junction function

The habitable attic ceiling in the over-rafter system serves a dual purpose: insulation of the horizontal part of the ceiling between collar ties (where the rafters do not reach) + preparation for the interior finish.

The solution according to the Gór-Stal catalogue: termPIR® AL laid between collar ties of the timber ceiling, closed from above with an OSB board (load-bearing sheathing, allowing walking on a non-habitable attic), and from below by a hanger + CD60/UD substructure + plasterboard as a suspended ceiling.

Key point: between the termPIR® boards and the plasterboard substructure, leave a gap of 2–4 cm — for routing electrical installations and to accommodate movement of the timber structure.

Critical installation aspects

• termPIR® AL boards between collar ties — width must be cut individually (the spacing of collar ties never exactly matches the 60 cm module); fill any gaps around the collar ties with assembly foam.
• Aluminium tape (item 05) on ALL board joints — failure to maintain vapour tightness = condensation within the insulation layer on the cold side (on the OSB), eventually leading to moisture build-up and degradation.
• OSB from above — lay with a 3 mm expansion gap between boards, fix with screws to the collar ties (not to termPIR®).
• Hanger (item 06) fixed exclusively to the collar tie (timber) — penetrating the insulation layer would compromise the vapour-tight barrier.
• Plasterboard substructure (item 07) — typically CD60 + UD on the floor + ES hanger; profile spacing according to the plasterboard manufacturer (usually 40 cm).
• Rooms with high humidity beneath the roof — additional PE vapour barrier foil under the termPIR® boards, laid over the 2 cm gap and sealed with tape.

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

Documentation

Technical Catalogue termPIR® — Residential Buildings (Gór-Stal 2022), page 16 — Pitched roof, over-rafter system, ceiling detail. Scale 1:10.

Components in this junction