Basement window — three-layer basement (termPIR® AL)

Junction function

Basement window in a three-layer wall = basement window from the two-layer wall (page 47) + additional complexities of the 3-layer construction: two lintel layers (item 04) — load-bearing + facing. Geometry as in the three-layer wall window (page 41), but below ground level = more challenging water protection.

Key differences vs above-ground three-layer window (page 41):

1. Bitumen behind the window frame (item 09) — continuation of the waterproofing behind the frame; without this, capillary water enters the basement interior.
2. Sill with 10% slope (vs 5% above ground) — faster water runoff from the recessed geometry.
3. External basement light well (Velux UWB / Aco SF) — recommended for a basement window.

Critical installation aspects

• Bitumen behind the window frame (item 09) — continued BEHIND THE FRAME + over the facing lintel (item 04, external part); waterproofing tightness is the priority.
• Load-bearing + facing lintel — independent, each with its own reinforcement; in a three-layer clinker wall, the facing lintel = prefabricated brick / clinker element with reinforcement.
• termPIR® AL strip above the facing lintel — eliminates the linear thermal bridge; 8–15 cm thick.
• Sill (item 12) with a minimum 10% slope, 30 mm drip edge projecting beyond the facing facade; EPDM 200 mm on mesh beneath the sill.
• Installation foam (item 14) — low-expansion mandatory; greater humidity fluctuations in basements = greater structural movement.
• Basement light well (Velux UWB / Aco SF) — recommended for a basement window with opening level below grade; the drainage grate at the bottom of the well must be connected to the perimeter drainage.

Documentation

Technical Catalogue termPIR® — Residential Buildings (Gór-Stal 2022), page 47 — Three-layer basement wall, basement window detail. Scale 1:10.

Components in this junction