We are going to hang a drywall ceiling in a bathroom remodel. It has trusses on 24" centers. I have been given advice by a professional drywall hanger who says I should use 5/8" green board. Other professionals have said I can use 1/2" regular drywall. I have used 1/2" regular drywall on 16" centers for over 30 years (even in basement bathrooms with a shower) with no problem. I am doing this for my daughter and want to do it right. Please let me know what you think.

 

IRC R702.3.7 covers drywall thicknesses, and 1/2" is generally allowable by code. However experience has shown that 1/2" gypsum can sag if ceiling will also be holding insulation. If it is, I would recommend you use 5/8" rock. If no insulation, 1/2" is okay.

The footnote to the table 702.3.5 indicates that if the ceiling will be textured, 1/2" gypsum is no longer acceptable for a ceiling that is 24" OC. It must either be 5/8" or sag-resistant 1/2".

IRC R702.3.8.1 says not to use moisture resistant gypsum in areas subject to continuous high humidity. A bathroom ceiling would typically not have "continuous" high humidity... unless you have 12 girls using the same bathroom.

If your hanger and finisher recommends 5/8" I would go with his recommendation. If you are doing the work, it's your dime, your call.

 

IRC R702.3.8.1 says not to use moisture resistant gypsum in areas subject to continuous high humidity. A bathroom ceiling would typically not have "continuous" high humidity... unless you have 12 girls using the same bathroom.

The standards seem counter intuitive since you would think moisture resistant gypsum should be used in a high moisture area. What would be recommended?

 

The key word is "continuous". A bathroom is an area with occasional high humidity, so moisture resistant gypsum is a good idea, provided it is not in an area that will receive wall tile. Wall tile requires a cement backer board.

I would also caution you that the occasional higher humidity in a bathroom would be an additional reason to be cautious about choosing 1/2" gypsum for the 24" OC ceiling. Code allows it. But as some people fondly point out, the code is just a minimum requirement.

 

I'm not crazy about green board, the formulation that helps it resist moisture also makes it harder for the primer to adhere. Once the drywall is primed and painted with a latex enamel it will have all the moisture resistance it needs. While flat latex paint would allow the drywall to absorb moisture, enamel repels the moisture. I'd use 5/8" drywall on the ceiling.