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Roof and terrace waterproofing calculator

Enter the flat area, the length of walls where the membrane turns up and the height of that upstand, then the roll size, the lap and the number of layers from your product’s data sheet: PRAXAO gives the surface to treat, the membrane area with laps and waste and the number of rolls to buy.

Dimensions

m²

Total length along which the membrane turns up a wall (parapet, kerb). 0 if none.

m
cm

Material

As your waterproofing specification says: one layer, or several.

m
m

From the product data sheet: the width of each strip that is covered by the next.

cm

In litres per m², from the primer’s data sheet: no value is assumed.

L/m²
Advanced options
%

Enter the dimensions to see the drawing.

Calculation results

Fill in the fields to see the result.

Preliminary estimate from the values entered: not a structural validation and not an execution plan. Check the local rules and the manufacturers’ data.

Your last inputs are kept in this browser.

Results are provided for information. Check tax rates and legal requirements that apply to you.

How to use it

  1. Enter the flat area of the roof or terrace.
  2. Enter the length of walls with an upstand and its height (0 if none).
  3. Enter the roll width and length, the side lap and the number of layers from the data sheet.
  4. Read the surface, the membrane area and the rolls to buy.

Examples

40 m² terrace, 26 m of upstand 25 cm high, 1 m × 10 m rolls, 10 cm lap, 10 % waste

Surface to treat: 46.50 m². Membrane with waste: 51.15 m². One roll covers 9.00 m² once the lap is deducted: 6 rolls.

Frequently asked questions

Where do the roll size, the lap and the primer rate come from?

From the data sheet of the product you use. The values shown are only starting points: no product value is built into the tool.

Does it replace a waterproofing specification?

No. It estimates quantities. Drains, corners, joints, slopes and the method depend on the product and on a qualified applicator.

How are the laps counted?

On the width only: each strip loses the side lap. End laps and cuts are covered by the waste percentage, which you can raise for a complex roof.

Guides to go further

BUILNORA

Screed Calculator

Volume of floor screed and the cement bags, sand and water needed for your area and thickness.

BUILNORA

Tile Calculator

Number of tiles and boxes for a floor or wall, with grout joints and a cutting waste margin.

Quote Generator

Prepare a clear quote or estimate for your client, with validity date, taxes and totals, ready as PDF.