Technical analysis
Selecting an exterior membrane by assembly drying needs, rain exposure, mechanical demands and detailing quality.
Engineering scope
- Principle
- Higher vapour permeance is not automatically better if rain control and joints are inadequate.
- Verification
- Higher water resistance does not justify trapping construction moisture behind vapour-closed layers.
- Field control
- Compare a complete set of test data and confirm internal vapour control, exterior ventilation and details together.
System decision
Start with the actual roof or wall build-up, climate, indoor condition and risk at the relevant interface. Product data must be connected to a defined layer and detail.
Documentation and acceptance
Keep design details, approved product data, delivery labels, batch records, mock-ups, concealed-work photographs and repairs traceable to the installed area.