Sheathing, exterior insulation, and interior poly in Climate Zone 3A
I’ve got a lovely 1989 house on a moderately encap’d crawlspace, complete with wood lap siding and single-hung aluminum windows (not thermally-broken) . House needs work.
The windows have all had the IGUs replaced….poorly. All windows need to be replaced because they’re leaky, are racked because of bad IGU bonding, and are clear glass with high solar heat gain. That’s a story for my next post.
I’m thinking about replacing the siding along with the windows, for reasons of best practice for WRB and flashing details. Also, the siding has some pretty soft areas that are shedding paint, especially on the South side of the building, and around splash areas.
Now, for the fun part.
Problem number 1: ThermoPly. It’s ripple-y under the siding, which is not a great sign, and none of the penetrations for light fixtures, etc., are flashed or air sealed at all. Standard procedure for the time, I know. Currently I’ve got flat sills and some type of black poly sheet for flashing, which I assume is taped somehow to the ThermoPly.
I can’t think of a great way to flash new windows to existing ThermoPly without removing the siding, and at that point I’d rather replace with decent sheathing and a modest amount of sheet insulation.
Problem number 2: Poly sheeting on the interior side of the wall. Climate Zone 3A. It does not seem to be a issue at the moment (air leakage likely prevents problems), but with a proper WRB, etc., I’m wary of creating a moisture problem in the wall cavity.
What is the solution here? If I replace the sheathing and add a modest amount of exterior insulation, what would be the proper stackup of sheathing/WRB/insulation (insulation to the interior or exterior side of sheathing), and can the poly retarder be left as-is with no other changes depending on that order of stackup? Am I overly concerned with creating a moisture problem?
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