Vapor-open exterior sheathing
In building up a list of vapor open exterior sheathings to recommend for cold climates (with the goal of creating walls that can dry to the outside and can accomplish the recommended 5:1 outside to inside perm ratio), I've found myself a bit stumped by how to measure the permeance of traditional diagonal 1x white pine sheathing.
From ASHRAE the perm of solid white pine varies from 0.029 to 12 perm in depending on relative humidity, but what should the perm be estimated for a typical tongue and groove assembly with unsealed joints and variable thickness at the joints? I would assume it's substantially more permeable than solid pine would be on its own?
Building Science recommends 10 perms for wood siding based on leakage at the joints: http://www.buildingscience.com/documents/information-sheets/3-water-mana...
Anyone know more about more complex assemblies like this?
Other materials by comparison:
Fiberboard: 18-24 perm in
Gypsum Board (don't have number for fiberglass faced like DensGlass): 20-40 perm in
Plywood: 0-6 perm in
Homosote: (same as fiberboard?)
OSB: 0-3 perm in
Posted Fri, 07/30/2010 - 19:44
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