ZIP over Thermoply, bad idea? – GreenBuildingAdvisor

I’m thinking out loud here, and thinking far ahead.  Mostly thinking about sequencing and labor.

I’ve got a CZ3 house with Thermoply, and am starting to plan a small addition combined with other exterior work in the future (windows, siding, etc.).

Not planning on patching up the Thermoply with more Thermoply.  I’m not even sure if anyone sells it around here.  I don’t think it was ever taped or airsealed anyway.

I’m planning on fully sheathing the 4 small walls that are getting modified with ZIP instead.

I’m guessing that it’s really not a great idea to install ZIP over Thermoply, and the Thermoply should be removed first.  Sooo many nails (or staples).

Thermoply is listed as 0.6 perms, so that would be a fairly large area of Class 3 vapor retarder behind (and in contact with) the ZIP, with air leakage paths between the two. Probably fairly risky.

Am I thinking about this correctly?