Tar paper under (shiplap) sheathing and under siding. – GreenBuildingAdvisor

Morning all.

I have been renovating a 1970s addition on my house from the inside. Zone 4 with damp winters.

Current assembly is cedar siding, tar paper (probably #15), horizontal shiplap, tar paper (again), 2×4 studs with R7, vapour barrier, drywall.

From the inside, I’m replacing the r7 with r14, adding 1.5″ EPS (on stud faces) with taped seams and joined to adjacent poly vapour barriers. No doors or windows on this wall, and minimal electrical so it’s straightforward.

What I’m curious about is whether I should cut out the interior tar paper between the studs. I suspect the shiplap was the original siding and then they added tar paper and cedar on top. Now the shiplap is sandwiched between two layers of tar paper. As per local code and custom, the vapour barrier will be continuous and the first layer behind the drywall. Are the two layers of tar paper encasing the shiplap of any concern?

Thanks in advance.