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From what I understand the code usually discusses things like fire rating (not specific thickness) as they relate to required material, and also the fastener pattern and what thickness to use versus stud spacing.

However, I've also heard that 5/8" is specifically mentioned by dimension for use as attached-garage separation from living space.

Yet another person has told me that 5/8" is specifically required for residential ceilings.

I've been unable to confirm the specific thickness requirements in the IBC.

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You need fire rated drywall to separate the garage from the living space, so 5/8's was just short hand for fire rated. –  BMitch Aug 21 '12 at 17:51
    
@BMitch yes, I see that it specifically mentions "5/8 Type-X"... I'm asking if there are specific requirements for thickness which are not related to fire rating or rigidity requirements –  Matthew Aug 21 '12 at 17:52
    
AFAIK, sheetrock is not considered structural and in terms of code, is primarily a form of fire block. I can't think of any situation where code requires a thickness for anything other than fire rating (though I may very well be wrong...) –  DA01 Aug 21 '12 at 17:58
    
(Actually, I take that back, I believe sheetrock can be used for shear force bracing--which I personally find odd--but I guess that is to code in some situations) –  DA01 Aug 21 '12 at 17:59
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@dbracey, it's a pain, but much less so if you use a drywall lift. –  BMitch Aug 21 '12 at 18:31

2 Answers 2

up vote 4 down vote accepted

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.

Table R702.3.5

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.

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I think the answer in all of that was bullet point 'd'. –  BMitch Oct 11 '12 at 17:59

I'm not aware of any specific requirement for the thickness of drywall, only for fire ratings which are provided by 5/8" Type-X.

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