Lesson 3.3.1
Vapour diffusion and permeance
Vapour diffusion: moisture in vapour form moves through airspaces (rooms, wall cavities, material gaps) and through materials depending on their permeability. Driven by vapour pressure differences.
High permeance, allows vapour flow
- Gypsum board
- Fibrous insulation
- Latex paint
Low permeance, resists vapour flow
- Oil-based paint
- Plastic vapour barriers
- Foil-faced insulation