WRB-- House wrap(s) and Fanfold

Generally speaking–On some inspections you can see inside the walls due to drywall repairs being made, or from windows being installed during the time of inspection. My question to you guys is about going TOO FAR with housewrap/fanfold.
Owner was present/working on walls/installing windows/building materials visible in the wall during early spring 2022 inspection. House had been extensively remodeled on the inside in 2014 and had original 3/4" tongue and groove wood siding from 1920. The siding is the exterior wall, there is no substrate behind the siding.
There were some rot holes, nail holes etc, so the owner installed tyvek type house wrap (woven kind, not the typar kind) against the exterior wall from inside. Then insulation, drywall. A few years later, owner installed Typar brand (non-woven) house wrap on the home’s exterior, then vinyl siding.
I suggested to the owner and buyer that the two layers of housewrap (one inside/against the exterior wall, and the second installed from outside) may trap moisture within the building envelope. And to throw a curve ball into this, the contractor friend of the buyer said, “Yeah, should have put up fan fold insulation instead”, which is frankly stupid because fanfold is closed cell foam (100% No permeation) and would definitely have condensation on the side against the house! I told the contractor what I thought and he said, “Just don’t tape the joints and it’ll breathe.” Wrong, I say.
I really don’t know if the double house-wrapped (1 tyvek, 1 typar) house is a problem or not, or if fan-fold would have made it worse. So if anyone has any experience or thoughts on how to approach these in the future, let me know. I look behind siding and try to figure out the building envelope on all inspections, so I’ll see this happen again I bet. This inspection is over, further evaluation has been suggested in the report.

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It depends on the permeance of the house wrap.

For instance, Lowe’s had (has) one that is perm of 16, that I was aware of back in the day, and one that has a perm of 12 and probably others now.

Google is your friend.

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Think consequence. If its an old home, how is it performing? I see many homes from the 80’s and 90’s with vinyl siding and no house wrap. I always inform my client that the lack of house wrap may cause the home to be susceptible to moisture damage if water gets behind the siding. But due to limitations, I cannot determine if this condition exists. I typically make no recommendation for correction in this scenario unless I see damage or obvious water intrusion points.


Good points.

I just saw a different situation last week.

Drywall, blown-in Fiberglass (no paper on it, no vapor barrier at all), then exterior sheathing 3/4" plywood, then 2" foam insulation sheets, then vinyl siding.
I suggested further evaluation by a licensed contractor because I think the moisture will go through the drywall, into the insulation, slowly through the plywood and then dead-stop on back side of 2" foam. I’d say in the long run, that plywood will be enduring a lot of water.