Alternative to WRB
I need an alternative to a space that has no WRB.
I am working on converting an existing attached garage into a bedroom and bathroom. The garage has no WRB and we would like to avoid removing all of the siding to install one. The walls are totally exposed from the interior, so we are wondering if there is anyway to install an alternative WRB from the inside to prevent outside moisture/vapor from getting in the walls.
My first thought was to caulk the studs to the inside face of the sheathing and perhaps paint the inside of the stud bay with an elastomeric paint, then later install a vapor barrier after the insulation and beneath the drywall. If I do so, am I preventing the ability for the wall to dry on the exterior side?
For reference, I am located in Portland and the home is 75 years old.
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Replies
The purpose of WRB is to act as a second plane of protection against water intrusion, such as rain, while allowing water vapour to pass through it from inside to out, allowing the wall cavities to dry. It can have secondary functions such as keeping bugs etc. out of walls, and can be detailed as an air barrier.
It will be risky to create a finished conditioned space in your garage with no WRB on the walls. And some of the solutions you propose will be actively reducing the drying potential of the wall cavities.
I would either bite the bullet and install the WRB, or go without and keep your fingers crossed.
CPS,
As plumb_bob said, there is no interior alternative to a WRB which will perform the functions he catalogued, and the absence of one probably means the penetrations like windows and doors are not properly flashed - and some damage to the sheathing is occurring.
If you don't want to remove the siding, you can protect the wall cavities by treating it like a house with no sheathing. This article explains how: https://www.greenbuildingadvisor.com/article/insulating-walls-in-an-old-house-with-no-sheathing