Installing vapor barrier from the backside of the wall

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Jons999

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I live in a 1940s cape cod so there is a small attic area on each side of the upstairs bedrooms. The upstairs is obviously poorly insulated, gets very hot in the summer and cold in the winter. What I found is that the walls between bedroom and attic appear to have been insulated from the back after the drywall was up. The insulation (very thin, low r value) is stapled to the studs on the attic side leaving a 3” airgap between the drywall and the vapor barrier. What is the best way to correct this to have a good working vapor barrier? Spray foam?
 

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Was doing some more research and it seems that drywall (especially mine with popcorn finish) with multiple coats of paint on it is not very permeable to moisture. I’m thinking seal any possible air leakage between the interior walls and stud bay (outlets, baseboard area, etc) and not worry about vapor barrier? It is common for old house like mine to not have vapor barrier above the ceilings anyways.
 
I would say it is likely a lot caused by gaps and air leaks and wouldn’t be real concerned with the vapor barrier. Do you know what is in the sloped ceiling areas of the room for insulation and how the area is vented to the ridge?

We don’t have a cape cod but have a upstairs bathroom that was always cold/hot and it had a ceiling attached to rafters like that. I lowered the ceiling a little by adding 2” foam board and then covering that and it made a huge difference. I put the foam up with screws with giant plastic washers and then used can foam in all the seams and cracks.
 
Yeah I can see up to the ridge, has 2 layers of original old insulation with a black backing on it. Not up to todays standards but still fully intact. Attic is nicely vented. I pulled off some of the insulation on the walls and despite it being poorly insulated with basically non functional vapor barrier for 20 years or more the wood and drywall is still in brand new condition. No moisture damage or mold. So I’m not gonna worry about the vapor barrier and seal up any air gaps I find and put some Rockwool insulation in there.
 
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