Work out waterproofing area instantly with clear inputs, formula shown and shareable results.
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.
Area
Total m² = floor area + perimeter x upstand height
Quantities
Liquid coats = total x coats; membrane rolls = ceil(total x 1.15 / roll area)
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.
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.
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.