Waterproofing Membrane Calculator — m, m², cost
How to use this calculator
Pick a surface — a foundation wall takes perimeter × below-grade depth, slabs and decks use length × width, or enter a measured area in m². Choose a membrane: liquid at 1.5 mm DFT, self-adhesive sheet, drain board or dimple mat. The output is what you actually order: litres, rolls or sheets with primer and seam tape, sized for one delivery.
Liquid applied — ~1.5 m²/L at 1.5 mm DFT in two coats.
Sheet membrane — 1 m wide rolls, 150 mm side and end laps.
Drain board — 1.2 m × 20 m sheets (24 m²).
Dimple mat — 1.5 m × 20 m rolls (30 m²).
Saved Calculations
| Time | Surface | Area m² | Type | Qty | Cost |
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How to Calculate Waterproofing Membrane (Metric)
Choose the surface — a foundation wall takes area as perimeter × below-grade depth, slabs and decks use length × width, or enter a measured area in m². Apply 5% waste for simple rectangular walls, 10% for a typical job, and up to 15% where penetrations, steps, and corners increase cutting and detailing. Liquid is rounded up to whole litres and sheet products to whole rolls or sheets, since part-tins and roll ends are rarely reusable on site.
Below grade the membrane works as a system: the waterproofing coat on the wall, a drainage/protection layer, and free-draining backfill to a perimeter drain. Combine this with a house wrap calculator for the above-grade weather barrier and a vapour barrier calculator for under-slab and crawlspace film.
Formulas
Liquid applied: litres = (area × (1 + waste)) ÷ coverage, with coverage ≈ 1.5 m²/L to build a 1.5 mm dry film thickness in two coats. Sheet membrane: rolls = area ÷ net roll coverage after the 150 mm side and end laps. Drain board / dimple mat: sheets = area ÷ panel coverage (24 m² for 1.2×20 m, 30 m² for 1.5×20 m). Primer: litres = area ÷ 5 m²/L. Seam tape: linear metres ≈ perimeter plus interior seam runs, divided by 25 m per roll.
Standards
EN 13967 covers flexible plastic and rubber sheets for below-grade tanking; EN 15814 governs polymer-modified bituminous thick coatings (PMBC). Liquid systems target a minimum 1.5 mm DFT applied in two coats over a primed, sound concrete substrate within the manufacturer's temperature window.
FAQ
Primer required? Most systems require primer on concrete substrates; allow about 1 L per 5 m². Drain board vs dimple mat? Drain boards (XPS-based) add a little thermal value; dimple mats are lighter and more economical for drainage protection. How does this fit other trades? See the spray foam calculator for interior foundation insulation, the wall insulation calculator for above-grade R-value, and the carpet calculator when finishing the protected slab.
On install day
Three numbers estimators miss. 2025 EUR ranges — liquid PMBC €15–30/m², self-adhered sheet €25–50/m² installed, drain board €8–15/m² material; double those for finished installed cost with labour on a typical residential basement. The #1 mistake is forgetting the cant fillet at the footing-to-wall cold joint — every site inspector under EN 13967 / EN 15814 looks for it, and most contractors charge an extra 15–30 m of detail tape after backfill to fix it. Temperature window — most manufacturers require 5 °C+ rising for self-adhered sheet and most liquids; cold-weather primer is a separate line. Carry the membrane 150 mm above finished grade, lap the drain board over the footing, and tie into the perimeter drain on a 100 mm vapour barrier if there's a slab inside.
