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2mnyprjx 08-24-2010 10:10 AM

Moisture barrier on unheated garage?

I'm putting cedar siding on my house and have been putting Tyvek houswrap over the house prior to the siding. Have come to the attached garage. The garage is only attached to the house by a total area of about 7 x 10 feet. Garage is unheated with no insulation, just studs. Don't plan on heating it.

Question: Do I need to continue with the tyvek on the garage? The previous siding I'm taking off is 4 x 8 sheets of what i would call "plywood siding." The wall sheeting under the old siding is 5/8 inch plywood. There was no moisture barrier between the two, just plywood against plywood.

GBR 08-24-2010 06:02 PM

Welcome to the forum!

You may not need a water resistant barrier under lap siding. Check local B.D. How to Choose & Install Housewrap, Tyvek, Typar, HomeWrap, Building Sheathing Wrap - House Wrap - Building Exterior Moisture Barriers

However, the one you picked is problematic because of the cedar siding, unless you back-primed it first:
“Some surfactants, which are chemical
extractives that can leach out of wet
cedar or redwood siding, have the
potential to degrade a plastic housewrap’s
water resistance. However, surfactants
can also degrade asphalt felt.
“There have been problems with cedar
and redwood sidings leaching wood
sugars or surfactants,” says Lstiburek.
“This has occurred with all the plastic
housewraps and the felts. Everything is
affected. But the plastics seem to have
more of a problem than the felts,” he
says. Brad Allshouse from Simplex
agrees that surfactants can affect any
sheathing wrap. “The installer should
back-prime the siding, so the chemicals
can’t leach out,” he says.”

UMass Amherst: Building and Construction Technology Leaky Housewraps

Be safe, Gary

2mnyprjx 08-25-2010 10:22 AM

Thanks for the info Gary. Looks like I'm out of luck for the areas I've done already. Didn't back-prime the siding. I'll start back priming and might as well wrap the garage also.

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