Vent through foam?
agpalof
| Posted in Energy Efficiency and Durability on
If you are building a frame wall sheathed with OSB or plywood and then covered with foam on the exterior could the wall be “vented” to allow drying by using a hole saw to drill several 2″ holes in every stud bay thru the sheathing and foam? (the holes would have tyvek stapled over them prior to blowing in the celluose) With this method all framing would remain covered to prevent thermal bridging but there would be an exit path for moisture to escape
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
All I can see are headaches waiting to happen. How do you vent w/ out conducting heat through the vent material? Aren't you kind of killing your air sealing? EPS foam and plywood are already somewhat breathable, right? Maybe this is over-thinking? I do that all the time. "Leave well enough alone"??
Andy,
It seems that you fundamentally misunderstand the purpose of exterior foam. The foam is there to keep the wall sheathing warm. You want the OSB to be above the dew point so that it stays dry; if you drill 2-inch-diameter holes in the foam, you are creating cold spots that will be subject to condensation or moisture accumulation.
Warm = dry; cold = wet. You want the foam to be continuous. Swiss cheese won't work!
There is absolutely no reason to provide "an exit path for moisture to escape." During the winter, interior conditions (temperature and RH) will be different from exterior conditions. You want a good thermal barrier to keep these two conditions separate. You certainly don't want to provide paths that encourage the flow of moisture through your wall assembly -- that's a recipe for disaster.