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EPDM Roof Calculator — Membrane, Adhesive & Trims
Calculate EPDM rubber membrane sizing with 150mm upstand allowance per BS 6229:2025. Includes bonding adhesive, perimeter trim and water check quantities.
Length of the flat roof
Width of the flat roof
Minimum 150mm upstand at abutments per BS 6229:2025 (75mm only at accessible door thresholds with drainage)
Water-based deck adhesive ~3–4 m²/L (PermaRoof / Elevate RubberCover); check your datasheet
Extra for corners and overlaps
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How We Calculate This
This calculator sizes your EPDM membrane by adding upstand allowances to your roof dimensions, then calculates adhesive, trims and accessories.
The formula
Membrane size = (Roof length + 2 × Upstand) × (Roof width + 2 × Upstand)
Bonding adhesive (L) = Membrane area ÷ Coverage rate (m²/L)
Default coverage 3.5 m²/L is mid-range for water-based deck adhesive (PermaRoof quotes 3–4 m²/L; Elevate RubberCover up to 4.5 m²/L over timber). Contact adhesive for the 150mm perimeter strip and upstands is a separate, two-sided product (~3.5–4 m²/L) — always confirm on your datasheet.
Perimeter trim = 2 × (Length + Width) + 10% extra
Frequently Asked Questions
Measure your roof length and width, then add 150mm (minimum upstand at abutments per BS 6229:2025) on each side. EPDM is ideally installed as a single sheet with no joints. Common UK suppliers (Firestone, ClassicBond) offer sheets up to 15m wide.
EPDM uses two adhesives. The field is bonded to the deck with water-based deck/bonding adhesive — roughly 3–4 m² per litre one-sided (PermaRoof; Elevate RubberCover quotes up to 4.5 m²/L over timber), so this calculator divides the membrane area by 3.5 m²/L by default. The 150mm perimeter strip and upstands are bonded with two-sided contact adhesive at about 3.5–4 m² per litre. Always confirm the exact rate on your product datasheet.
The upstand is the membrane turned up vertically at walls, parapets and edges. BS 6229:2025 requires a minimum 150mm upstand above the finished roof surface to prevent water ingress. The upstand is secured with perimeter trim and sealed with water check tape. A reduced 75mm is only permitted at accessible door thresholds with specific drainage preconditions.
Quality EPDM rubber roofing has a life expectancy of 40–50 years. Firestone RubberCover carries a 20-year manufacturer’s warranty. It’s UV stable and remains flexible in cold weather.
EPDM is one of the most DIY-friendly flat roof systems. It involves applying contact adhesive, positioning the membrane, and rolling out air bubbles. Perimeter trims are screwed in place. Always work on a clean, dry deck. For comparing membrane options, see our Flat Roof Membrane Calculator. For GRP as an alternative, try our GRP Flat Roof Calculator.
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Last updated: March 2026
Verified against UK standards · estimates only, confirm with your supplier.