I see various references indicating that standard latex paint on gypsum wallboard is very roughly 6 perms (dry cup). Paints/primers designed to be vapor retarders are typically much lower (< 1 perm). But I also see that wet cup results are much higher - 17 perms in one case and if I understand it correctly, much higher than that here. I don't see wet cup results for the low perm latex paints. Perhaps there are paints out there that are "close enough" to smart membranes. Say ~1 perm when dry and ~10 perms when wet.

There currently aren't any paints with smart-vapor retarder type characteristics.

If there were you can bet kraft facers and expensive membrane type vapor retarders would soon be history.

If you look at the reference paper carefully you'll see that the vapor permeance of the latex only doubles going from about 25% RH to about 75% RH. To be an effective smart vapor retarder it would have to be something like a 5x permeance change (like OSB) or 10x (like plywood) over that relative humidity span to really make the difference, the way OSB and plywood behave:

http://buildingscience.com/sites/default/files/migrate/jpg/BSI087_Figure_03_sheathing_perms_web.jpg

So, while latex paint trends in the right direction with relative humidity, it's not the order of magnitude change that would make it really useful.

See figure 10 below for documentation of paint and gypsum acting as a fairly smart vapor retarder (~4 to 40 perms):

https://buildingscience.com/documents/building-science-insights/bsi-099-its-all-relative

Thanks for sharing. That Lstiburek guy is great. Love his seminars. Wish I could thank him personally for all his work and helping of others.

Currently building a ICF house with pool in basement open to the whole house, not in a room but will be covered almost all of the time. Exterior walls being ICF are low perm, so my only options for passive moisture control is at the ceiling.

The current state is drywall (not painted yet) and insulated with spray foam for air sealing (about 1/4 surface area) and to also help support drywall. Just put some blown in fiberglass at R20 to start. Plan to go above R60 as funds become available. I still have options of what paint to help control moisture. I also have a geo unit to dehumidify (I have calculated the moisture that will be coming off the pool and tested the geo at 50% humidity and it can pull the same amount of moisture out of the air, so don't think I will need a dehumidifier at this time)

Any comments are appreciated. The house is a ranch 3700 sqft on each floor with a 400 sqft opening between floors so very open concept. Pool is in basement. Located in Ann Arbor MI.

Went with fiberglass because I didn't like the idea of having 6000 lbs of cellulose in the ceiling.

You might blow some cellulose over the attic fiberglass - it will help with radiant and convection issues with fiberglass (ie, be more effective than just the added R value would suggest).

Yes Jonr, I like that idea but would like to hear from someone that has done it. Also wonder how thick you would need the cellulose.

Its a pretty good idea no doubt.

We did end up doing Vapor Barrier paint from Sherwin Williams. It worked out good and it has been 2 years with no problems.

We spray foamed the attic trusses to the back side of the drywall for sealing in and added strength. House achieved a ACH of .79 We didn't put a whole lot of foam in, just enough to do what I said. We then added R80 fiberglass. Cellulose is way to heavy in my opinion.