Drywall Thickness for the Ceiling

[Beltzington]

Still trudging along with my master bath redo, I am about ready to hang drywall and was planning on using water resistant green-board on both the ceiling and walls. Unfortunately no one locally carries 5/8" thick green-board. This leaves me two options, go with 1/2" green board on the ceiling or standard 5/8" drywall on the ceiling.

Ceiling joists are 24" OC and code does not require type x fire proof drywall however from research I am concerned 1/2" may be on the marginal support side especially with a textured ceiling. Specs for 1/2" green board say it is approve for 24" OC as long as it is perpendicular to the rafters which it is.

Should I be more concerned with moisture damage or drywall sagging?

 

[Raspy]

I'd go with the standard 5/8" in your case. Especially on 24" centers. Sealed and painted it should not have a problem in a humid bathroom.

 

[Cord]

Code will require the use of a moisture resistant drywall in the bathroom.

1/2" likes to sag ever so slightly when it spans 24". If the room is small you won't see the sag. If it's a big or long room with a window at the far end to cast shadows you might see the drywall waves. Generally residential rooms are small enough that you won't see them.

You are correct on not needing a fire core drywall. Fyi, generally, type C is used on ceilings and type x is for walls. If you want to find a unicorn, try searching for moisture resistant type c.

 

[nikdfish]

If sagging is a concern, what about adding joist blocks (maybe w/ just 2x4) for additional support points/grid for the drywall?

 

[dstig1]

If you use the newer high strength 1/2" drywall, it should be fine. My whole house uses that (also 24" OC trusses), except where the 5/8" type X was required around the garage. I think they add some fiberglass fibers to it

 

[downsizingnow48]

In this situation I would use two layers of 1/2" green board. Cost of materials and labor time minimal.

 

[quicksandfarmer]

In New England it's customary to run 1x3's perpendicular to the joists on 16" centers on ceilings. That will solve your span issue. You may want to check if it meets your requirement for fire blocking.

 

[lance429]

You might want to head on over to Amazon and search for "The Gypsum Construction Handbook". There are used copies for less than $2.

I'm not sure where you are looking for advice on spans but after many years in the construction business here's what I've learned.

1/2" MMR wallboard is generally NOT recommended for over a 12" joist spacing as it is more flexible than regular drywall and tends to sag. 5/8" is recommended for no more than 16" span. Adding more layers doesn't stop the sag very well as the sheets aren't bonded and each is free to move on it's own. The added weight of a textured ceiling would aggravate the tendency to sag.

It is worth noting that just as structural framing maximum span tables relate to structural soundness, maximum drywall spans may relate to structural soundness not smoothness for drywall or any feeling of bounce in marginally sized floor joists etc.

If you have another reference with different info please post a link. I'm always willing to learn. And I can't speak to the fiber reinforced drywall mentioned by dstig1. The only fiber reinforced stuff I ever worked with was very high density prefinished wallboard for modular office walls.

Be sure too use galvanized drywall screws and not the usual black oxide screws. Use a vapor barrier under the wall board, especially on exterior walls and ceilings. If you are a "belt AND suspenders" kind of guy hit the finished wallboard with two coats of high quality clear water based urethane. Follow the manufacturers recommendations for time between coats. Then paint with a couple coats of high quality paint.


Lance

 

[EddieWalker]

I do quite a few bathroom remodels every year and I never remove the ceiling sheetrock. I'll cut all sorts of holes in it for new lighting, vent fans and getting wires or plumbing through the top places of a wall, but I leave the sheetrock in place so the insulation doesn't all fall out on my and add more work to the job. Then when I'm done with all my rough in work, I just put another layer of new green sheetrock up over the old stuff with 2 inch screws.

If you have already removed the sheetrock from the ceiling, then you really want the added moisture protection of the green board. While some bathrooms have more moisture/steam to deal with then others, it's just a small increase in cost to use it. Ideally, you want 5/8's for 24 inch spacing because in some cases, 1/2 inch will sag sometimes. Not always, but it does happen. If you are debating the risk, figure out how much weight you will be putting on the sheetrock with insulation. The older stuff was really heavy. New blown in insulation like Attic Cat is super light. Older homes also have a huge amount of dust and debris laying on top of the sheetrock, adding to the tendency to sag. Finally, how long have your joists been in place? Is there any chance of them sagging? The reason for popcorn texture was that some of the joists might sag just a bit, and the popcorn hid that imperfection. Smoother ceiling textures show this more easily in larger rooms. Using flat paint on the ceiling stops the reflection of light, which shows the imperfections. How big is the bathroom? Will you be able to go from wall to wall with a single sheet? or is it one of those huge bathrooms?

The vast majority of homes have half inch sheetrock on their ceilings. It's very very common. Going with half inch is a small gamble, but one that so many people take that the odds of you having any issues is extremely remote.

 

[EddieWalker]

Just to add to my previous comment. I only use exterior paint in bathrooms. It's designed for outdoor use, in all weather conditions, and I feel it's much better at dealing with the humidity and steam created by a shower. Bathroom paints are basically an interior paint with an anti fungal added to it that doesn't work in any of the bathrooms that I've seen it used, especially rentals. Of course, the better the venting, the better off you will be.