I’m renovating a townhouse, meaning I have a front and back exterior wall but my side walls are shared with my neighbors. Obviously I cannot do the traditional thing and put Zip on all sides.

I was planning to put Zip on the front and back, and have a different type of airtight membrane on the interior walls. However, the question remains, how do I transition between these two?

The easiest answer is to tape the interior air barrier against the back of the Zip sheathing. However, I don’t know whether this counts as a continuous air barrier — is the OSB itself airtight, or just the green layer on the front? If I tape the interior air barrier to the inside of the OSB, is air going to pass through the side of the OSB into the house?