Hello DIY'ers quick question i could use some help with, I Live in California my home is a 1 story home, im remodeling the home, when i removed the ceiling drywall there is no vapot barrior between the insulation and the drywall. Im replacing the insuraltion with R-30 Bats Unfaced. Once finish the whole home im going to put blow in insulation over that. Do i need to install a Vapor Barrior between my drywall and bats insulation. My Attic has good ventalation, ive installed a few attic fans previously.
Next, it is very unlikely that you need a vapor retarder level of any sort in this case. While doing the remodel, the best bet would be to air seal all the top plates, penetrations, and other air barrier breaches in the attic floor/ceiling.
Google air sealing and you will find a bunch of results.
Once you let us know where in CA you are, the final answer on the vapor retarder can be given.
The fact that you have very good ventilation and will insulate sufficiently eliminates the necessity for a vapor barrier in large part.
I would prefer to see passive ventilation but that is another discussion altogether.
as mentioned, the attic fans.... don't turn them on. they create a lesser pressure in the attic and encourage air to flow to it from the conditioned space. just let it vent naturally, with about 150 to 300 to 1 ratio of attic space to vent area. see a local authority for your number, where to place the soffit vents, etc.