Vapor Barrier Calculator — m, rolls, cost
How to use this calculator
Pick the application — crawlspace floor, interior wall, under-slab, or a custom area. Choose PE foil thickness (0.15-0.5 mm) and roll size, then set seam overlap (15-30 cm) and a waste allowance for trimming around piers, ducts, and penetrations.
Rolls drive the order quantity; the area shown with overlap is what actually gets unrolled on site. Seam tape and acoustic sealant are the difference between a working sd-value retarder and a barrier that fails the next time the dew point swings.
Saved Calculations
| Time | Application | Area m² | Rolls | Cost |
|---|
How to Calculate Vapor Barrier
Measure the surface to cover — crawlspace floor, interior wall, or under-slab. For crawlspaces, add the wall run-up height so the PE foil wraps a short distance up the foundation walls and is sealed to them. The estimator converts that area into rolls after accounting for seam overlap losses and a trimming waste allowance. Under-slab membrane works alongside the below-grade waterproofing estimate and the gravel/sand bed beneath the slab.
Formulas
Base area = length × width. Crawlspace total = floor area + perimeter × run-up height. Overlap factor = roll width ÷ (roll width − overlap), since each strip loses its overlap to the adjacent strip. Adjusted area = base area × overlap factor × (1 + waste%). Rolls = ⌈adjusted area ÷ roll coverage⌉. Seam length drives the tape quantity; perimeter drives the acoustic sealant tubes.
Membrane Thickness Guide
0.15 mm — standard PE foil for most crawlspaces and under-slab per EN 13984. 0.25 mm — heavy-duty for high-traffic crawlspaces. 0.38 mm — premium, puncture-resistant. 0.50 mm — commercial grade, reinforced per DIN 4108-3. A PE vapor barrier controls moisture but is not air or thermal insulation — pair it with wall batt or board insulation, an air-sealing spray foam layer, exterior house wrap, and the right attic/roof RSI for the assembly to perform.
FAQ
How much overlap? Minimum 15 cm for floor applications and 30 cm for wall seams per DIN 4108-3; all overlaps are taped. Do I tape the seams? Yes — every seam and any tears or penetrations get approved vapor-barrier tape. Do I need sealant? Apply acoustic sealant at all perimeter edges where the membrane meets foundation walls, piers, columns, and pipe penetrations. Which side faces the conditioned space? In cold climates the barrier goes on the warm-in-winter side; under slabs it sits directly beneath the concrete on the gravel base. For finished floors over a crawlspace, coordinate with the floor covering takeoff.
On install day
Budget €0.80–2.20/m² for 0.15 mm PE foil and €3.20–6.00/m² for 0.25–0.38 mm reinforced membrane in 2025; encapsulated crawl jobs run €30–75/m² installed once tape, mechanical fasteners, and termination strips are added. The single most common takeoff mistake is forgetting that overlap is a loss, not just a detail — a 110 m² crawl with 30 cm overlaps on a 2 m roll actually consumes ~130 m² before waste. For under-slab pours per EN 13984 and DIN 4108-3 always order a reinforced 0.25–0.38 mm membrane — the thin 0.15 mm foil that survives an unheated shed pad will be shredded by rebar chairs and a power trowel on a finished basement. Tape every seam, every penetration, and pre-cut boots for plumbing before the concrete crew arrives.
