Where is a waterproof breathable membrane installed?

It is generally installed outside insulation or structural sheathing as a secondary water and wind control layer that permits outward drying.

How is a vapour barrier different?

A vapour barrier controls indoor vapour and air entry, usually on the warm side or another position confirmed by hygrothermal design.

Can a breathable membrane replace the primary roof waterproofing?

No. Roof panels, primary waterproofing, flashings and drainage still follow the project roof design.

Is one overlap width suitable for every project?

No. Slope, drainage direction, wind pressure, substrate, restraint and product instructions all affect the required lap.

Does EN 13501 Class E apply to a complete roof or wall?

No. The classification applies to the tested sample and stated field of application, not automatically to every product batch or complete assembly.

What should be checked at delivery?

Check product identity, dimensions, quantity, batch labels, packaging, appearance, reports and retained samples, then map the batch to the installed area.