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In a two storey house, is 5/8" drywall required on the ceiling of both the first floor ceiling and the upstairs ceiling? Or is it only required between the second floor ceiling and attic space as a fire separation?

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    Hello, and welcome to Stack Exchange. Where are you located? – Daniel Griscom Dec 18 '16 at 2:30
  • Is your stud and joist spacing 16" or 24"? – Jim Stewart Dec 18 '16 at 13:40
  • Would your preference for 1/2" hold if you were upstairs and there was a fire downstairs? You can exceed code minimum requirements, and the cost for doing so is not all that large, generally. One advantage on the upper floor is that it supports modern levels of attic insulation better and with less tendency to sag. – Ecnerwal Dec 19 '16 at 3:21
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Thickness of gypsum board has nothing to do with upstairs or downstairs. It has to do with spacing of supports: ceilings = 1/2" on 16" on center and 5/8" on 24" on center. (A 1/2" board will sag over time from support to support if it spans too far.)

Likewise thickness of gypsum board has nothing to do with "party walls". The Building Code requires fire wall SYSTEMS. There are many systems that use 1/2" Type X and some that use 5/8" Type X. It has to do with spacing of supports, nailing pattern, and use of insulation.

By the way, the Building Code also requires a minimum sound rating rating in "party walls" too. Often we'll use the sound wall SYSTEM criteria as the governing criteria, and just specify that the board be fire rated (Type X) and kill two bird with one stone.

Now, if the space is in a moist environment, (porch, steam bath area, etc.) we'll bump up the thickness for ceiling gypsum board, (I.e.: 1/2" to 5/8" thick on supports at 16" on center.)

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I am Contractor in Massachusetts, learned my trade in Vermont from old timers. I have been thought to build things like you mean it, though. Gentleman that took me and thought me how to renovate older homes never believed in 3/8 - 1/2 drywall for interior walls or 1/2 inch drywall for ceilings and exterior walls. I have been on my own since 2001 and I have been always using 5/8 on the ceiling and all of the exterior walls as well. Interior walls I use 1/2 inch. Bathrooms roxul insulation and then quateboard. Inspectors were more then satisfied.

Don’t be afraid to go above minimum code use 5/8 drywall or blue board insulate your bathrooms, buy quality doors and be happy.

  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know how better to contribute here. – Daniel Griscom Jun 13 at 16:29
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That I am aware of, 5/8" is required only in garages or perhaps other areas where there are flame spread issues. Only on walls and ceilings that neighbor living spaces.

I am only guessing but condos and apartment buildings will require it on ceiling between floors of living spaces. In single family homes, I have never seen it applied like your question asks. It can be used for firestopping in concealed places required by code.

  • Some construction practices specify and maybe new codes require 5/8" drywall when the stud and joist spacing is 24" rather than the traditional 16" spacing. A type of modern construction that is supposed to be especially energy efficient uses 2 x 6 exterior studs spaced at 24". This is said to allow better insulation, less thermal bridging, and less weight of wood while maintaining structural integrity. – Jim Stewart Dec 18 '16 at 13:19
  • Fire codes aside, I would definitely use 5/8" drywall if the studs are 24". Otherwise your walls are going to flex a lot more than you would like and probably sound a lot more hollow than you would like when you bump them. – Craig Dec 19 '16 at 2:18
  • May I humbly add folks, I built my personal home in 1989 from the ground up, used 2X6 for the walls at 24" on center so I could maximize the insulation. Now it is a code thing to do the same, in 1989 it wasn't. The span of the plywood sheathing on the outside became more of a concern since the inspector wanted the plywood standing up the 8' tall way, even though the whole wall was sheathed in plywood. The drywall on the inside did very well. I never really ever had an issue with bumping the walls, yes I got close, but never an issue for the 25 years I lived there. – Jack Dec 19 '16 at 15:17

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