vapor barrier over a shower
I am rehabbing a bathroom under a sloping attic roof. The ceiling is just above head height. Should the ceiling insulation have a vapor barrier or not? I have heard various opinions on this – some say the shower vapors will get trapped between the drywall and the vapor barrier and form mold and rot the drywall. Should this ceiling be made of drywall or cement board?
I would use Water Resistant drywall and paint with high gloss kitchen/bathroom recommended paint.
The key to preventing mold is to move the moist air the hell out of there. Use a proper size of exhaust fan and you should be fine.
I also use a proper vapour barrier under all drywall installations. I don't know your location so it's hard to comment on it.
*Yes to insulation. Yes to vapor barrier. Yes to drywall. Use moisture resistant type ( ie greenboard)This is also a good time to install an exhaust fan.
*And, Shel, do not turn off the fan when you stop the shower. Let it empty the bathroom moisture. Genel.
*and shel..all the above.. except....This is also a good time to install an exhaust fan. nah.... this is the time.. when you absolutely have to install a bath fan..if you're gonna tile.. skip the water resistant drywall and go straight to cement board or hardibacker.. use a fan/light... it will encourage users to turn it on... and leave it on as gene said....
*Use a fan with a humidistat. Automatic on and it shuts off at the right time. Buy the best fan with the lowest sone rating.
*And, since you're gonna need to install that fan/light, make sure the unit is "approved for damp locations". This may also require that it be placed on a GFCI protected circuit. Don't skimp on the fan size or cost (added cost will get you both capacity and quietness). Now is not the time to try to save $50 to $75... think of the long term problems with mildew, etc. which you will minimize. Most bathroom exhaust fans make so much noise that people don't like to use them.The idea of a humidistat is a good one. Another good idea is that of a timer for the fan. It can then run for a while after the party is out of the shower, removing the lingering moist air from the bathroom.Good luck, Steve
*wow - lots of great ideas. No wonder I look forward to my issue of Fine Homebuilding more than my issue of JAMA.....
*I agree with most above but I have to ask all what you think of the greenboard manufacturers specs that say it is not for use on ceilings only on bath walls...Also it is not recommended as a tile under layment in a direct wetted area...near the shower stream reading my drywall handbook,aj
*I think the reason they say not to use it on ceilings is because it tends to sag - but I seem to recall reading that it should be OK if the rafters are 16" o/c and not 24", and if the greenboard is laid lengthwise perpendicular to the rafters, not parallel with the rafters
*I'm with aj. (by the way aj, what does the shower hand book say?) My advise on green board is just say no. If you need the "protection" green board is supposed to offer, you need something else. The green board may not fall apart, but the paint will peel. Use a vapor barrier, tile backer, and tile set with thin set mortar.
*Steve...It says it gets wet in the shower and melts in your hand!near the stream gonna have ta get a waterproof copy,ajGreenboard is a joke...and is not for ceiling use.
*Water-resistant gypsum wallboard is a close cousin to standard drywall. Crushed gypsum is combined with water to make a slurry, then formed between paper layers. Although there are other ingredients, the basic component of the core is gypsum. In water-resistant varieties, wax is added to the core, and the characteristic green-paper face is treated with silicone, Chapman says. Other than the green paper (which is why these panels are often called "green board"), there are no obvious differences between it and standard drywall. It is typically available in thicknesses of 1/2 in. and 5/8 in. Panels are 4 ft. wide and 8 ft., 10 ft. or 12 ft. long. Chapman says MR board is often mistaken for a vapor barrier. But with a perm rating of between 24 and 25, he says, it isn't (building materials need a perm rating of 1 or less to be classified as vapor-diffusion barriers). Builders also have been known to install tile-covered green board over a vapor-diffusion barrier, such as polyethylene sheeting, on exterior walls. Wrong. According to Chapman, a wall of tile and mastic becomes its own vapor barrier. If you put a second barrier behind it, any moisture getting through the wall tile becomes trapped, degrading the core of the drywall. Even kraft-faced fiberglass batts should be avoided on outside walls covered with gypsum board and tile. In addition to walls, green board can be hung on ceilings but never on framing spaced wider than 16 in. o. c.--and that's for 5/8-in. panels. For 1/2-in. board, ceiling framing should be no greater than 12 in. o. c. When hanging a ceiling, always install panels so that the long edge is perpendicular to the framing. Because of the paper plies, drywall is less susceptible to sagging when applied this way. Grain direction doesn't make much difference on walls, Chapman says. ---------------------------------------------------------------------------------- Scott Gibson is a freelance writer in Connecticut. From Fine Homebuilding #133, pgs. 138 and 140.
*this sounds exactly like the article I read, which is what caused me to pose the question in the firts place, especially the part about even avoiding Kraft-faaaced fiberglas batts
*Again I find myself a tad behind, but I must agree with a.j. and steve g. green board is an elaborate hoax. even if the stuff was truly waterproof(which it isn,t) what about the taped joints. ever seen a drywalled shower enclosure with bubbled or peeling joints. I've seen plenty. drywall of anykind has no place in the shower. p.s. humidistats have a habit of been turned off to avoid running all day and night, I like the fan/light combo better.
I am rehabbing a bathroom under a sloping attic roof. The ceiling is just above head height. Should the ceiling insulation have a vapor barrier or not? I have heard various opinions on this - some say the shower vapors will get trapped between the drywall and the vapor barrier and form mold and rot the drywall. Should this ceiling be made of drywall or cement board?