Technical analysis
Why a functional membrane can resist liquid water while permitting water vapor diffusion through a roof or wall assembly.
Engineering scope
- Principle
- Liquid water is resisted by pore structure, surface energy and functional layers; vapor transport is driven by vapor-pressure differences.
- Verification
- The membrane works only when external drainage, ventilation, laps and penetrations remain continuous.
- Field control
- Do not use exterior vapor openness as a substitute for interior air and vapor control.
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.