Vapour pressure
Course Handbook: Level 3 Award in Energy Efficiency Measures for Older and Traditional Buildings, published by Historic England in December 2024, defines vapour pressure as: 'The pressure exerted by molecules of water vapour in gas form. This can exert considerable force — for example, enough to blister paint. Warm, moist air has a higher pressure than cold, dry air. A high moisture content will create a large amount of vapour pressure. Vapour diffuses through building materials at a rate proportional to the vapour pressure difference. If one side of a wall is much dryer than the other, the vapour will diffuse faster.'
See also Saturation vapour pressure
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