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Why no "ridge vents" for walls?

I've been thinking about wall insulation vs. attic insulation. Why is it that ventilation is not needed in wall assemblies using fiberglass or cellulose insulation in the same way that it is needed for roof assemblies. I certainly know this is true, but discover I'm not clear on the science behind it. For old 2x4 walls, I think it might be because the insulation is thin enough so the dew point isn't reached within the assembly. But what about double stud walls and other higher insulation assemblies?

Asked by Hallie Bowie
Posted Jan 10, 2013 4:37 PM ET
Edited Jan 10, 2013 4:59 PM ET

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Hallie,
The short answer to your question: if you are building a double-stud wall, you should definitely include ventilation. The ventilated air gap between the siding and the wall sheathing is usually called a rainscreen gap.

I have been recommending the practice for thick walls for some time; for example, see How Risky Is Cold OSB Wall Sheathing?

Answered by Martin Holladay, GBA Advisor
Posted Jan 10, 2013 4:58 PM ET

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