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?
Drywall thickness requirements
drywall
Related Solutions
International Residential Code (IRC) has a table for that.
Chapter 7 - Wall Covering
SECTION R702 INTERIOR COVERING
R702.3 Gypsum board.
R702.3.5 Application. Maximum spacing of supports and the size and spacing of fasteners used to attach gypsum board shall comply with Table R702.3.5. Gypsum sheathing shall be attached to exterior walls in accordance with Table R602.3(1). Gypsum board shall be applied at right angles or parallel to framing members. All edges and ends of gypsum board shall occur on the framing members, except those edges and ends that are perpendicular to the framing members. Interior gypsum board shall not be installed where it is directly exposed to the weather or to water.
For SI: 1 inch = 25.4 mm.
a. For application without adhesive, a pair of nails spaced not less than 2 inches apart or more than 21/2 inches apart may be used with the pair of nails spaced 12 inches on center.
b. Screws shall be in accordance with Section R702.3.6. Screws for attaching gypsum board to structural insulated panels shall penetrate the wood structural panel facing not less than 7/16 inch.
c. Where cold-formed steel framing is used with a clinching design to receive nails by two edges of metal, the nails shall be not less than 5/8 inch longer than the gypsum board thickness and shall have ringed shanks. Where the cold-formed steel framing has a nailing groove formed to receive the nails, the nails shall have barbed shanks or be 5d, 131/2 gage, 15/8 inches long, 15/64-inch head for 1/2-inch gypsum board; and 6d, 13 gage, 17/8 inches long, 15/64-inch head for 5/8-inch gypsum board.
d. Three-eighths-inch-thick single-ply gypsum board shall not be used on a ceiling where a water-based textured finish is to be applied, or where it will be required to support insulation above a ceiling. On ceiling applications to receive a water-based texture material, either hand or spray applied, the gypsum board shall be applied perpendicular to framing. When applying a water-based texture material, the minimum gypsum board thickness shall be increased from 3/8 inch to 1/2 inch for 16-inch on center framing, and from 1/2 inch to 5/8 inch for 24-inch on center framing or 1/2-inch sag-resistant gypsum ceiling board shall be used.
e. Type X gypsum board for garage ceilings beneath habitable rooms shall be installed perpendicular to the ceiling framing and shall be fastened at maximum 6 inches o.c. by minimum 17/8 inches 6d coated nails or equivalent drywall screws.
I'm not aware of anything special for fire rating a joint in drywall, just use the same joint compound and tape you would use on the rest of your walls. Fire rated drywall will cut similar to normal drywall, but it will offer a lot more resistance because of the embedded fiberglass.
When sealing any gaps or cracks, they make special fire rated expanding foam and caulk. They tend to be orange in color. There's also fire rated insulation that can be used for any utility chases/bulkheads that connect to the ceiling.
For junction boxes, we've been required to box our in on common walls (2x4 above and below the junction and a piece of plywood behind everything) to ensure that any shorts in the electrical couldn't travel to another unit, but I doubt this would be a requirement for anyone in a single family home.
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Best Answer
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.)