How to repair vapor barrier on older home, CZ5A? – GreenBuildingAdvisor

Greetings,

We are having some electrical work done, and the electrician cut some pretty big holes into the interior side of an exterior wall.

This is a late 1970s home in north IL, but the area where the work is being performed is an addition, maybe from the 90s. 

This is CZ5A, so I was surprised to see a poly plastic sheet used on the interior (I’m used to seeing Kraft faced batts).  Exterior wall assembly as I understand it, is [interior] drywall, poly vapor barrier, 2×4 wood stud with fiberglass batt, plywood sheathing, wood siding [exterior]

I could use some advice on the following  3 things:

1. How to best integrate the new electrical boxes into the air/vapor barrier?  I’d typically default to using the proper air/vapor boxes, but what about all the other existing electrical boxes where work isn’t being performed?  So my initial thought was to tape/seal the vapor barrier at the typical metallic box face/edge and caulk the plate for a better air seal. I checked the sheathing near the existing electrical boxes and it looked to be in good shape (photo attached).

2. What to do about the large holes in the vapor barrier the electrician made?  I figured I’d carefully cut back more drywall around the holes already made and then stitch in new vapor barrier with an overlap and tape the seams. But what vapor product type to use?  Similar poly to match existing or something like intello plus?

3. Theoretically speaking, how bad is it to leave up poly on the interior in CZ5A? I know it’s not typically used anymore, and a Type II vapor retarder is more common in mixed humid climates and this assembly. The backside of the sheathing does look really good around the electrical boxes, so I’m inclined to not worry.

Some photos attached for reference:

1. Example of the large holes electrician made in the drywall

2 and 3. Sheathing near an existing electrical box

4. How the poly was cut around an existing electrical box in a different area we have opened up, but the vapor barrier wasn’t disturbed. 

Many thanks! Scott