Flat roof calculator — PIR boards, fasteners and adhesive
Calculate the number of PIR boards for a flat roof with pack count, volume and an indicative U-value referenced to the limit for your indoor temperature (0.15 / 0.30 / 0.70 W/(m²·K)). The calculator also selects telescopic fasteners (sleeve length, screw per deck type) or PU adhesive consumption with edge-band surcharge. Single or double layer with separate thickness choice per layer. Instant result — no registration.
Deduct openings larger than 1 m².
5% simple plan · 10% many openings
Roof plan — board layout
0 full 0 cut
Full board Cut board Edge zone — densified fixing per design
Edge band = 1/8 of the shorter side (indicative). Layout is illustrative — joints staggered min. 250 mm on site.
Frequently asked questions
How many PIR boards for a 100 m² flat roof?
With 1200×2400 mm boards (2.88 m²) — about 35 boards + 5% reserve ≈ 37 pcs. The calculator includes deductions and manufacturer packing.
What PIR thickness for a flat roof?
Depends on indoor temperature: heated (≥16°C) → U ≤ 0.15 ≈ 150 mm; halls 8–16°C → U ≤ 0.30 (≈70–80 mm); buildings <8°C → U ≤ 0.70.
One or two insulation layers?
A single layer with profiled edges (LAP/TAG) is fully valid. Two FIT layers with joints staggered by half a board side, min. 250 mm reduce joint bridging at high thicknesses. In two-layer systems the bottom layer gets 1 preliminary fastener/board, the top layer the full count through both layers.
How many telescopic fasteners?
Manufacturer base scheme (Gór-Stal): 8 pcs per 1200×2400 board, 2–4 pcs per 1200×600. Final quantity per EN 1991-1-4 wind design — edge/corner zones typically 8–12 pcs/m². Sleeve length ≈ insulation thickness minus 15 mm.
Glue or mechanically fix PIR on a flat roof?
Mechanical — any deck (standard on steel decks). PU roofing adhesive — concrete, old felt, even steel deck crowns, at ≥ +5°C on a clean, dry substrate (board format and adhesive pattern per design); consumption min. 150 g/m² in beads, +50% at edges, double at corners.
What about roofs over 1000 m²?
Coverings > 1000 m² must be Broof(t1) with combustible insulation separated from the interior by min. RE 15 (Polish regulations). Classification applies to specific build-ups — see our article on 8 tested Broof(t1) configurations.