Tar Paper on INSIDE of exterior plywood sheathing?
Hey there! First post here as I’m going crazy trying to find an answer to this.
I’m DIY renovating a house built in 1977, located in coastal British Columbia. I’ve removed drywall and insulation to find most of the walls (upstairs and downstairs) have black paper in the wall cavity against the exterior plywood (see photo).
A couple walls have it installed outside the sheathing, as I would expect, but only on the lower floor near the covered car port and entry.
I’ve checked that between the ply and siding (siding is wood based panelling from what I can tell), there is no paper or house wrap of any kind, and no rain screen – unless the area I checked (by removing the dryer vent) is an anomaly.
The house has really good roof overhangs on the front and back, and the sides are adequate, so I haven’t seen rain water hitting the walls at all unless the wind is really really blowing.
My dilemma is: should cut away the paper and eventually replace it with house wrap outside the plywood once I redo the siding, and add a rain screen (probably within 10 years). Or should I leave it? I imagine adding house wrap later will create a weird problem, having two layers of paper with plywood sandwiched in the middle.
I’ll be adding a 6 mil vapour barrier before hanging new drywall, so I’m worried about moisture getting stuck in the walls with so many layers!
Anyone know why they would have installed the paper on the inside, and what I should do going forward? Any help would be very much appreciated!
Sean
Replies
I have dealt with this on 2 houses - one built in 1977 and the other in 1935, but remodeled in 1980. I live in Oregon. It was the thing to do back then I guess.
In both cases, I put addition tar paper over the existing exterior plywood siding (T-1-11), then 1/2" battens for a rainscreen, then new siding. I talked with a couple of builders and an inspector (engineer) and they all recommended this. I did not do any further interior air barrier. Here, the poly vapor barrier on internal walls is considered a bad idea. They stopped it quite a while ago.
I did worry about the "rot sandwich", but using tar paper on the outside isn't going to cause that. It will dry if moisture gets in. I wanted a drainage plane inside the rain screen cavity, and not a whole lot more. Also, I was extremely fussy about the details where siding met trim, windows, doors, etc. I made sure these would not allow water in. One of the houses is on the beach and gets a load of wind and rain.
After a few years on each - no problems to report. My garage has open wall cavities on the inside, and I can't see any moisture at all.
Best of luck to you.