Under-Slab Membrane Calculator
Estimate a stated membrane strip layout for a rectangular slab, then see coverage, cut demand, whole-roll ordering, seam length and optional cost separately.
Part of the Concrete & Masonry calculators — see all tools in this category.
Under-slab membrane
Lay out user-specified membrane strips for a rectangular slab, then distinguish target coverage, cut demand, whole-roll purchases, tape seams, and optional local pricing.
Preparing calculator controls…
| Net target coverage | 26 m² |
|---|---|
| Gross strip-cut area | 27.3 m² |
| Purchased whole-roll area | 44 m² (2 rolls) |
Current result
Purchase 2 whole membrane rolls.
- Net target coverage
- 26 m²
- Gross strip-cut area
- 27.3 m²
- Purchased membrane
- 44 m²
- Selected tape seams
- 6.2 m
Net coverage is the extended slab footprint. Gross cut area includes full-width strips and the entered side lap once; it is not the purchase quantity. Whole-roll stock rounds the strip layout up, so purchased area can exceed cut demand. The tape length follows only the selected seam policy. A blank roll price is an incomplete, unpriced line—not a zero-cost quote. Tape, accessories, labour and every installation scope remain excluded unless separately measured and quoted.
- End joins are disabled; a strip longer than one roll is rejected.
- This is a user-specified quantity layout, not a membrane-system, lap, tape, or suitability specification.
| Material | Net need | Order quantity |
|---|---|---|
| User-specified under-slab membrane roll | 27.3 m² (ordered) | 44 m² (ordered) (2 packs) |
No prices entered
Cost breakdown
No prices entered. This is not a completed zero-cost estimate.
| Line | Purchased quantity / unit / basis | Pricing state | Direct price | Entered line tax |
|---|---|---|---|---|
| Under-slab membrane rolls | 2 count (ordered) | Not priced | — | — |
- Direct priced subtotal
- $0.00
- Selected contingency base
- $0.00
- Contingency rate
- 0%
- Contingency amount
- $0.00
- Before-tax total
- $0.00
- Entered line tax
- $0.00
- Contingency tax (not entered)
- $0.00
- Final total unavailable — enter a price to begin the estimate
- —
Missing price categories: Under-slab membrane rolls.
Cost by category
No entered prices to chart.
| Category | Cost | State |
|---|---|---|
| Under-slab membrane rolls | Not priced | not-priced |
How it works and assumptions
Enter the measured slab, the selected edge extension, actual roll dimensions, stated side lap and strip direction. The calculator expands the target footprint, lays full-width overlapping strips across it, and rounds the resulting strip layout to whole rolls.
This is a quantity worksheet, not a vapor-barrier specification. Continue with the live Mesh & Under-Slab Membrane Layout guide, then manually record compatible whole-roll quantities in the Itemized Slab & Shed Base Estimate guide; neither guide transfers results or creates an exporter.
Worked example
The independent example below uses different dimensions and stock from the default C14 UAT values, so it checks strip and whole-roll rounding without repeating the starting layout.