W2 roof to ceiling junction (termPIR® AL GK)

Function of the junction

The pitched roof meeting the attic ceiling is the characteristic “corner” in an attic room where the roof slope drops to ceiling level. In the W2 system the corner is formed by:

• termPIR® AL GK board (item 07) — continued from the roof onto the collar tie (i.e. the same material on the wall and ceiling).
• Timber purlin (item 12) supporting the collar tie.
• Acrylic corner finish (item 11) masking the joint between the roof and ceiling boards.

Geometry: two layers of AL GK meet at the purlin (item 12) at an obtuse angle (typically 120–135°). To avoid a visible gap as the timber structure moves (the collar tie and rafter respond differently to humidity changes), the corner is finished with flexible acrylic instead of gypsum filler (which will crack).

Critical installation aspects

• Low-expansion PIR foam (item 10) — fills the 5–10 mm working gap between the AL GK boards on the roof and ceiling; essential, otherwise there will be an air bridge.
• Flexible acrylic (item 11) — paintable/decorator’s acrylic-based sealant, NOT gypsum filler. After light tooling the gap is painted over with the rest of the interior.
• Purlin (item 12) — the timber structure must be securely anchored in the gable wall or on posts; it works in bending under the load of the collar ties.
• Between-rafter insulation (item 06) ends at half the height of the collar tie — going further makes no sense (the attic space is unheated).
• Wind barrier (item 04) terminated at the eaves + with a 10 cm return onto the front of the gutter to drain off any condensation.

Used in the pitched roof — termPIR® under rafters system.

Documentation

Technical Catalogue termPIR® — Residential Buildings (Gór-Stal 2022), page 27 — Pitched roof W II, roof to ceiling junction detail. Scale 1:10.

Components in this junction