| Scenario | Inputs | Expected output (approx.) |
|---|---|---|
| Floor sheet membrane |
Floor: 12 m × 8 m (96 m²) Lap: 10% • Waste: 5% Roll: 20 m × 1 m (20 m²) |
Gross sheet area ≈ 110.9 m² Rolls needed ≈ 6 rolls |
| Wall DPC strip |
Perimeter: 40 m DPC width: 150 mm (0.15 m) Lap: 10% • Waste: 5% |
Net strip area = 6.0 m² Gross strip area ≈ 6.93 m² |
| Liquid wall coating |
Perimeter: 40 m • Height: 2.8 m (112 m²) Waste: 5% • Coats: 2 Coverage: 3 m²/L/coat |
Gross area ≈ 117.6 m² Liters ≈ 78.4 L |
- Floor area (net): Floor length × Floor width
- Wall strip area (net): Perimeter × (DPC width in meters)
- Sheet area (gross): Sheet net area × (1 + lap%) × (1 + waste%)
- Rolls needed: CEIL(Sheet gross area ÷ (Roll length × Roll width))
- Liquid area (gross): Liquid net area × (1 + waste%)
- Liquid liters: (Liquid gross area × coats) ÷ coverage
- Primer liters: Liquid gross area ÷ primer coverage
- Costs: Quantity × unit cost; totals are summed.
- Select the scope: floor sheet, wall strip, liquid coating, or any mix.
- Enter geometry: floor dimensions for floors, perimeter for walls, height for liquid coating.
- Set allowances: lap percentage for sheets and wastage for all materials.
- Enter product data: roll size and unit cost, then coating coverage and coats.
- Press Calculate. Results appear above the form.
- Use Download CSV or Download PDF to save outputs.
Material takeoff for floor membranes
This calculator converts floor length and width into net area, then applies lap and wastage allowances to produce a practical membrane takeoff. For example, a 12 m by 8 m slab is 96 m² net. With 10% laps and 5% waste, the gross planning area becomes about 110.9 m², helping avoid shortfalls during detailing and perimeter upturns.
DPC strip quantities from perimeter
For wall strips, the tool multiplies the wall perimeter by the selected DPC width. A 40 m perimeter with a 150 mm strip equals 6.0 m² net. The same lap and waste factors are then applied, producing roughly 6.93 m² gross for ordering. This approach fits foundations, cavity trays, and horizontal barrier lines where strip width is consistent.
Roll-based ordering and rounding control
Sheet membranes are purchased in rolls, so the calculator divides gross sheet area by roll area and rounds up to the next whole roll. With a 20 m × 1 m roll (20 m²), a gross requirement of 110.9 m² becomes 6 rolls, providing 120 m² total. The surplus is shown as rounding excess, which you can redeploy for repairs, overlaps, or phases.
Liquid coating consumption by coats and coverage
When liquid wall coating is selected, the calculator uses perimeter × height to get wall area, adds wastage, then converts to liters using coats and manufacturer coverage. A 40 m perimeter at 2.8 m height is 112 m² net; at 5% waste it is 117.6 m² gross. With 2 coats at 3 m²/L/coat, consumption is about 78.4 L, plus optional primer based on primer coverage.
Cost visibility for procurement and planning
Unit costs are applied to rolls, coating liters, primer liters, and an optional labor rate per m² on net treated area. This structure separates material cost from installation effort and supports scenario testing, such as changing roll sizes, increasing coats in wet zones, or adding wastage for penetrations. The CSV and PDF exports preserve the calculated breakdown for quotes.
FAQs
1) What is the difference between DPM and DPC in this calculator?
DPM is modeled as a sheet membrane over floors (area-based). DPC is modeled as a strip along walls (perimeter × strip width). Both can share roll-based ordering if you choose a roll size.
2) Why do laps and wastage increase the sheet quantity?
Laps account for overlaps at joints, corners, and junctions. Wastage covers cutting losses, detailing around penetrations, and damage allowances. The calculator multiplies net area by both factors for safer ordering.
3) How do I choose a realistic waste percentage?
Simple rectangular slabs may use 3–5%. Complex layouts, many penetrations, or tight sequencing often need 7–12%. If you are unsure, start at 5% and adjust after checking the installation method.
4) How are liquid coating liters calculated?
Liters = (gross wall area × coats) ÷ coverage per liter per coat. Coverage should come from the product data sheet and can vary with substrate texture, moisture condition, and application method.
5) Should I always include primer?
Not always. Some coatings require primer on porous or dusty substrates, while others are self-priming. Use the primer option if your specification or product guidance includes it, and enter the stated primer coverage.
6) Why does the calculator round rolls up?
Rolls are sold as whole units, so partial rolls cannot be purchased. Rounding up avoids shortages. The tool also shows the rounding surplus so you can plan for overlaps, repairs, or spares.