How to Calculate Waterproof Sheet Quantity
Waterproof sheet quantity depends not only on the installation area but also on overlap width and waste factor. Getting these right prevents costly shortfalls on site.
Formula
Effective Width = Sheet Width − Overlap / Area per Roll = Effective Width × Roll Length / Required Area = Installation Area × (1 + Waste Factor) / Rolls = ⌈Required Area ÷ Area per Roll⌉
A standard 10 cm overlap is typical for most waterproofing applications. Add 10% waste for regular shapes and 15–20% for irregular or sloped surfaces. Ordering one or two extra rolls provides a safety buffer for unexpected field conditions.
Frequently Asked Questions
Most manufacturers recommend a minimum 10 cm lap, with 15 cm or more for critical areas like roofs and basements.
Standard rolls come in 1.0 m, 1.2 m, 1.5 m, and 2.0 m widths. Choosing the right width for your layout reduces cut waste.