Concrete Vapor Barrier Calculator
Estimate concrete vapor-barrier rolls, purchased membrane area, approximate seam length, surplus and material cost from slab dimensions and roll coverage.
Default project preview
2 rolls
Slab area
1,500 ft²
Order area
1,725 ft²
Coverage per roll
1,500 ft²
Approximate strips
2
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Slab length
Enter this project assumption in ft. The current imperial default is 50 ft.
Slab width
Enter this project assumption in ft. The current imperial default is 30 ft.
Overlap and waste allowance
Enter this project assumption in %. The current imperial default is 15 %. Minimum: 0. Maximum: 50.
Membrane roll width
Enter this project assumption in ft. The current imperial default is 15 ft.
Membrane roll length
Enter this project assumption in ft. The current imperial default is 100 ft.
Price per roll
Enter this project assumption in per roll. The current imperial default is 265 per roll. Minimum: 0.
How to read the outputs
Slab area
length × width. Default preview: 1,500 ft².
Order area
15% overlap and waste. Default preview: 1,725 ft².
Coverage per roll
entered roll dimensions. Default preview: 1,500 ft².
Approximate strips
across the 30 ft slab width. Default preview: 2.
Approximate seams
before perimeter and penetration detailing. Default preview: 50 ft.
Membrane allowance
rolls × entered price. Default preview: $530.00.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Slab area = length × width. Order area = slab area × overlap/waste factor. Rolls = round up (order area ÷ roll area).
Reviewed project guidance
How to use this estimate in a real project
Last reviewed: July 30, 2026
Estimate under-slab vapor-retarder rolls and seam tape from slab area, overlaps, penetrations and perimeter turn-ups.
Calculation steps
- 1Measure slab footprint by placement.
- 2Add required lap and perimeter allowances.
- 3Account for penetrations and grade-beam interruptions.
- 4Round rolls and tape separately.
Worked numerical example
A 40 ft × 60 ft slab is 2,400 ft². Adding 10% for laps and penetrations gives 2,640 ft²; divide by the roll’s net coverage and round upward.
Purchasing and rounding
Use a vapor retarder meeting project puncture, permeance and durability requirements; protect it during reinforcement placement.
Interpret the result
Quantity does not select the membrane class or resolve sub-slab moisture design.
Page-specific assumptions
- Flat slab footprint.
- Net roll coverage accounts for overlaps.
- One membrane system.
Common mistakes
- Using gross roll area.
- Puncturing membrane without repair.
- Leaving penetrations unsealed.
Primary and technical references
BuildMeter provides planning estimates, not engineering, architectural, electrical, mechanical, plumbing, permit or code approval. Review the methodology and verify final decisions with product documentation and qualified professionals.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Concrete Vapor Barrier Calculator questions
Why include overlap and waste?+
Sheet overlaps, perimeter turns, penetrations, cuts and damaged areas increase membrane usage beyond the flat slab area.
Does this calculate seam tape?+
It provides an approximate straight seam length only. Perimeter, penetrations and repair patches require additional tape and accessories.
Can any plastic sheet be used?+
Material selection depends on the project specification and expected service conditions. Confirm the exact membrane product before ordering.