Is it a code requirement or even necessary to use mold and moisture resistant drywall imediately over or on the ceiling of a one piece fiberglass shower enclosure? It does not appear to be common practice with production home builders large or small in southern California, although I have seen one home builder that uses it on the walls just over and along the sides of the enclosure. I’ve also noticed drywall does not extend over the screw flange as recomended by the manufacturer’s installation instructions. I have read many post’s that say stoping the “rock” at the flange and filling the void with a setting type compound is a commom and even preferred method? I asked my local building inspector and gave him the choise between the two methods and his opinion was that the factory method in his mind would be less prone to cracking over time due to the factory instruction’s of using silicone sealant in a maximum 1/4 gap between the rock and shower enclosure.
Thank you 🙂
Replies
jzr
As far as code requirement, not under the one I work on in NW Oh.
The old moisture resistant drywall I felt, decomposed even quicker than reg. board. The new is a bit sturdier and maybe better suited to it's application. The mold proof current product, might be better, I have no proof either way. Properly installed and maintained, regular board does just fine.
I would rather fur out around the flange to bring the plane of the frame out beyond it and it's fasteners. To me, this makes a nicer install. Holding it up and filling in keeps solid contact of compound right down on the ledge of the enclosure. Hollowing out the backside takes away half of what holds the gypsum together. If moisture gets at it, it can go quick.
I hold the board slightly away from the plastic, caulk that joint flush with the board-it's there for seal, not for looks-but don't slop it on, you're going to flat tape over that. When done mudding, I take a utility knife or sharp blade and score the bottom of that joint, then do a nice finish bead of caulk around the entire perimeter.
On peiced enclosures, I'll caulk a damn at the tub level joint to keep the water from traveling along that crack and behind the board.
Drywall type over shower stall
Calvin,thank you for the reply.
Just one of my concerns was having a butted seam near where the highest moisture levels would be both in terms of durability and astetics, if I were to only use the moisture resistant drywall immediately over the shower stall. Also, after having installed Kraft faced fiberglass insulation in the entire ceiling, I learned from my code book that a vapor retarder should not be used under moisture resistant drywall. some where I read doing this forms a double vapor barrier,and moisture may become traped between the two. Funny thing is during all this I asked a building inspector and he said it was OK to use these materials together. So after all the confusion I'm favoring just going with regular 5/8' drywall according to what I have heard up to this point on this forum and what I have actually seen in new construction. The vapor barrier was a whole other issue on to itself trying to determine if I actually need one. I've researched the California title 24 literature the IRC ,IBC and the Department of energy web site just to name a few.Any additional thoughts or details would be greatly appreciated
Thanks again
jzr
The only additional thought, get a good quiet exhaust fan and put it on a timer.
Then, use it.
Standard MR drywall does not create a vapor barrier. (Don't know about some of the newer stuff, but I doubt that they do either.)