Replacing cedar shakes on 96 yr old house – vapor barrier?
Where we were: 96 yr old Seattle (4c climate) house w/ exterior stack consisting of boards nailed to studs with cedar shakes over boards.
Where we are: Two areas of exterior siding ~4ft x 4ft each need replaced (boards & shakes) due to water damage from a leaking interior drain pipe.
Where we’re going: Installed 3/4 OSB where boards were removed. I saw Tom Silva installing a Benjamin Obedyke rain screen on siding prior to replacing cedar shakes on a similar build (https://www.youtube.com/watch?v=q9gaTrPybPg) and I bought a couple rolls. Doesn’t look like he went with any kind of house wrap. Can I/should I forgo adding house wrap? The shakes that I bought are double primed (aka crazy expensive).
Additional info: Due to the leak, the interior room behind the damaged siding is now a gutted bathroom/full 2-da-studs remodel. As the current strategy to let the house soak up water, breathe & dry out has worked for 100 yrs I am reluctant to add any sort of cavity insulation. It’s a very small bathroom, and the walls will be Schluter Kerdi Board as half the bathroom will be a steam shower. Contemplating putting up XPS boards between studs/Kerdi leaving cavities open. Thoughts?
Thanks,
Josh
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Replies
What you want is for the interior wall to be an air barrier and a vapor barrier, the exterior wall to be vapor open, a water barrier and an air barrier. If you get that down then insulating the wall should be no risk.
Thanks, DC!
Looking quickly at the Tom Silva video, it looks like there is a black material under the Slicker Classic. I bet it's #30 felt or tar paper, which is not an air barrier but does make a decent WRB, especially in conjunction with the Slicker Classic.
I agree with DC--you absolutely do not want a vapor retarder on the exterior; your wall should be able to dry to the exterior. Limiting the amount of air and moisture that can get into the wall from the interior is a good idea, though.
Thanks again, Michael.
Follow up question: Enough of the exterior wall cedar shakes have been removed I am inclined to add #30 WRB to the entire wall. The 3/4 OSB the water mitigation crew installed to replace the damaged siding sits 1/4" recessed to the legacy boards. A 1/4" OSB sheet added to the 3/4" OSB gets me flush. Can I simply nail the 1/4" OSB to the 3/4" and then add the WRB/Slicker Classic & shakes? Originally in crisis mode I was going to install the Slicker Classic where the OSB was to get it flush and leave the remaining exposed boards as is and cedar shake over everything. This seems more thorough but I also don't want to over complicate things.
That would probably work, but the more OSB you add, the lower the perm rating, when ideally the perm rating would be similar to the original boards. How much area of OSB do you have? Ideally, I would remove it, furr out the framing and install 1/2" plywood or OSB. Or install new boards similar to the original boards.
3' x 4' OSB on the side that gets rain and 4' x 5' on the side under a staircase awning that is completely sheltered from rain. I know what you mean about the perm rating. I'm thinking it's a small enough section I can probably squeak by. Thanks again, and if you have any other additional thoughts lemme know!~