ARCC 3202 Chapter Notes - Chapter 8-12: Vapor Barrier, Vapor Pressure, Air Barrier
16 Jan 2016
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Vapour barriers: need vents in eifs drainage plane. Not to aid in draining but to stop solar driven water vapour. Permeability of houswrap let slar heat push moisture into wallsystem. Must vent at both top and bottom. Can decrease moisture by 20: wall systems aren"t designed for modern home operaion, vb is stabled to interior face of stud wall. Airconditioning causes moisture to condense on the back of the polyethylene: increases probability and severity of cond. Condensation causes peeling paint, mould, rotting framing and sheathing. Poly eliminates ability of a wall to dry inwards. Straube suggests getting rid of poly and just using a vapour. Lets in 100x the vapour but that"s okay: controls wintertime diffusion and lets enough vapour past in the summer to stop condensation. Diffusion is low in winter: am is to stop condensation. Use xps if you cant install drainage layer= has outboard resistance. Housewraps lose waterproof nater when exposed to surfectants.
