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Waterproofing Area Calculator

Work out waterproofing area instantly with clear inputs, formula shown and shareable results.

About Waterproofing Area Calculator

Waterproofing area is the horizontal surface plus the upstand carried up the walls, perimeter times upstand height, which is where most failures actually occur. Liquid systems multiply that area by the number of coats, while sheet membrane needs a 15 percent allowance for laps.

Formulas

Area

Total m² = floor area + perimeter x upstand height

Quantities

Liquid coats = total x coats; membrane rolls = ceil(total x 1.15 / roll area)

Worked example

With the default values below, Waterproofing Area Calculator returns Area to waterproof of 47.80. Change any input above and every figure here is recalculated in your browser.

Inputs used

Floor areaminimum 0.1 m²
40 m²
Perimeterminimum 0 m
26 m
Upstand heightminimum 0 m
0.3 m
Number of coatsminimum 1
2

Results

Area to waterproof
47.80 m²
Upstand area
7.80 m²
Total coated area
95.60 m²
Membrane rolls at 10 m²
6

Step by step

  1. 1Values used
  2. 2Area
  3. 3Quantities
  4. 4Area to waterproof= 47.80 m²
  5. 5Upstand area= 7.80 m²
  6. 6Total coated area= 95.60 m²
  7. 7Membrane rolls at 10 m²= 6

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Waterproofing Area figure worked out?

Total m² = floor area + perimeter x upstand height. Waterproofing area is the horizontal surface plus the upstand carried up the walls, perimeter times upstand height, which is where most failures actually occur.

How high should the upstand be?

At least 150 mm above finished floor level generally, and 1.8 m or more in shower zones. Terminating below the wet zone simply relocates the leak.

What values do I need to enter?

This calculator takes 4 inputs: Floor area, Perimeter, Upstand height, Number of coats. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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