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RE: Ventilate stud spaces in earthquake retrofits?[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Ventilate stud spaces in earthquake retrofits?
- From: "Thor Matteson" <thor(--nospam--at)yosemite.net>
- Date: Mon, 16 Feb 2009 11:54:00 -0800
I'm not sure I understand which walls you are talking about--the common wall between the house and the garage, or the exterior garage walls?
For exterior *garage* walls, I would not worry about ventilating stud spaces or providing a vapor retarder at all. First, there is very little vapor generation in a garage (unless your clients have their laundry facilities there and use prodigious amounts of hot water). Second, garages are fairly 'leaky', and you would get some air exchange with the outside (especially when the garage door is opened) that would let moisture dissipate. Third, and perhaps most important, is that the garage temperature is usually going to be quite close to the exterior temperature--in that case even if there is vapor in the air it will not condense in the wall cavity because there is little temperature change through the wall thickness.
If you are talking about the common wall between the house and the garage, it is unclear as to why you can't insulate the stud spaces (with vapor retarder facing the warm side of the wall). Another alternative is to use a vapor retarding paint on the interior (living space) side of the wall. (Glidden used to make "Insul-Aid" for this purpose--I have no idea if it's still available.)
Do building departments in your area require sheet-rock on *all* garage walls? CBC only requires fire-resistive construction between the garage and living area, not on all exterior garage walls. Umm, unless they sneaked something into the 2007 CBC that I'm not aware of.
Thor Matteson, SE
("the other Thor")
Subject: Ventilate stud spaces in earthquake retrofits?
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I'm faced with a quandary concerning ventilation of the stud spaces when
installing plywood sheathing on the interior side of wood stud exterior walls of
garages to improve their earthquake strength/safety.
I'm not talking about the exterior walls of crawl spaces, where it is
standard practice (around here) to provide holes in the plywood sheathing near the
top and bottom of each space, to allow for air circulation within the stud space
and thus prevent possible buildup of moisture which could damage the wood
framing. I understand that such moisture buildup may occur in sealed spaces due
to temperature cycling, etc., and thus would occur only in exterior walls.
I see this situation as a smaller version of the need to ventilate crawl
spaces to prevent moisture buildup for the same reason.
I'm talking here about the exterior walls of garages integral with a
residence, which must have drywall for fire protection and cannot have holes in the
drywall and plywood sheathing. These spaces are not conditioned and normally
their exterior walls would not be insulated.
My usual practice is to specify ventilation holes in the new plywood
sheathing of all exterior walls, "unless the wall is insulated and has a vapor
barrier" (on the interior side). I have encountered little resistance to this
because it usually involves only one wall, costs little, and improves the "climate"
in the garage to some degree.
But now I have a situation where we'd *really* like to know whether this is
necessary, or even desirable. I know little of the physics of this
nonstructural condition, basing my recommendations for this aspect on "hearsay" over the
years, and a couple of more formal recommendations. I image it depends
quite a bit on the local climate. Here in the (San Francisco) Bay Area we have a
very mild climate, but a very large earthquake threat, so retrofitting walls
with plywood, etc., is very common, and highly recommended for practically all
TIA for any advice/guidance anyone can provide. I'm counting on y'all! ;)
Ralph Hueston Kratz, S.E.
Richmond CA USA
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