How to flash & air seal retrofit penetrations when a rain screen is present
My intention with this question is to get a general answer that can be used for different penetration types, claddings, and climate zones, because no such answer seems to be available anywhere at present. That said, I will include my specific details, so that we can avoid a “it depends” scenario.
Setup:
climate zone: 2 (hot-humid)
cladding: Hardie fiber cement lap siding
rain screen: Coravent, typical dimensions maybe 3/8″
sheathing: Zip system with liquidflash
insulation: R-15 mineral wool (i.e. 2×4 cavity)
inner wall: drywall
I would like to penetrate this wall with 3″ schedule 80 pvc conduit. The problem is I do not know how to water and air seal this penetration given that access to the sheathing is blocked by the cladding.
In my specific case, the indoor penetration is in a hidden area, so I do have good access from that side. I’ve seen some strategies for air sealing from the inside, but they tend to ignore the possibility of water infiltration by not utilizing any flashing or shingling.
What are the best practices for doing this?
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Replies
I don't know the answer, and curious what others say, but one thought would be to cut out an oversized square, flash yonth sheathing as typical for your WRB system, then simply add a trim block at the cladding level to cover the oversized cut. Would probably need a piece of z flashing at top of block, but just to kick water off the cladding (not back to the sheathing).
Otherwise it seems you'd be ripping off sections of siding then reintegrating.
bhr,
As Tyler said, it's much easier to deal with every exterior penetration (pipes, outlets, light fixtures, duct terminations) in both new construction and retrofits, when they are placed on a mounting block. You can make them yourself or buy pre-made ones.
It's a good high level suggestion, but I struggle with the details. It seems to me that the mounting block would itself prevent you from accessing the WRB/air barrier to properly seal it up. The devil is in the details.
I've watched people install mounting blocks prior to cladding installation, and the methods they used are not compatible with the situation I find myself in. Tyler's suggestion makes sense, but it's a suggestion of using trim; in which case, I find myself wondering how to install z-flashing behind that trim.
bar,
The hole necessary for the mounting block should be big enough that you can get at and seal whatever it is you are running through the sheathing and WRB, install a lapped head-flashing, and slide the block into place. Then all you need to do is caulk the sides and bottom of the block.