CRC · California Residential Code
Ceiling finishes, gypsum attachment and diaphragm fastening
This page orients you to the CRC sections that set gypsum ceiling finish rules, attachment/fastener requirements, and diaphragm fastening and sizing (see §R805, §R702.3.5.1, §R702.3.6, §R804.3.7).
Last reviewed: July 6, 2026
Overview
This hub summarizes the California Residential Code (CRC) rules that govern ceiling finishes, the attachment requirements for gypsum board, and the fastening and design of horizontal ceiling/roof diaphragms. It points you to the operative sections that specify minimum materials, fastener types and spacing, blocking and diaphragm lengths, and where gypsum may — and may not — be used as a diaphragm or finish. See §R805.1 for ceiling installation provisions.
Gypsum attachment requirements (screw types, penetration, and special limitations for textured finishes) are set out in §R702.3.5.1 and related gypsum construction rules; horizontal gypsum diaphragm criteria (minimum thickness, allowed framing spacing, shear capacities and fastening schedules) are in §R702.3.6 and Table R702.3.6.
Ceiling diaphragm and roof–ceiling connection details (required diaphragm lengths at gable endwalls, edge blocking, and fastener spacing such as panel-edge and field screw spacing) are prescribed in the roof‑ceiling construction chapter, e.g. §R804.3.7 and its figures/tables — these give the fastening schedules (edge screws at 6 in. o.c., field screws at 12 in. o.c. for typical gypsum diaphragms) and when reductions or multipliers apply for blocked or closely‑spaced fasteners.
In this section
Code references
Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:
CRC § 3.5 High relevance — show source text
FIGURE R804.3.5(1)—ROOF OR CEILING OPENING
For SI: 1 foot = 304.8 mm.
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ROOF-CEILING CONSTRUCTION
FIGURE R804.3.5(2)—HEADER TO TRIMMER CONNECTION
MINIMUM 2 IN. × 2 IN. CLIP ANGLE WITH 4 NO. 8 SCREWS THROUGH EACH LEG, BOTH SIDES OF CONNECTION
For SI: 1 inch = 25.4 mm.
R804.3.6 Roof trusses. Cold-formed steel trusses shall be designed and installed in accordance with AISI S230, Section F6. In the absence of specific bracing requirements, trusses shall be braced in accordance with accepted industry practices, such as the SBCA Cold-Formed Steel Building Component Safety Information (CFSBCSI) Guide to Good Practice for Handling, Installing & Bracing of Cold-Formed Steel Trusses. Trusses shall be connected to the top track of the load-bearing wall in accordance with Table R804.3, either with the required number of No. 10 screws applied through the flange of the truss or by using a 54-mil (1.37 mm) clip angle with the required number of No. 10 screws in each leg.
R804.3.7 Ceiling and roof diaphragms. Ceiling and roof diaphragms shall be in accordance with this section. R804.3.7.1 Ceiling diaphragms. At gable endwalls a ceiling diaphragm shall be provided by attaching a minimum [1] / 2 -inch (12.7 mm) gypsum board or a minimum [3] / 8 -inch (9.5 mm) wood structural panel sheathing, that complies with Section R803, to the bottom of ceiling joists or roof trusses and connected to wall framing in accordance with Figures R804.3.7.1(1) and R804.3.7.1(2), unless studs are designed as full height without bracing at the ceiling. Flat blocking shall consist of C-shaped or track section with a minimum thickness of 33 mils (0.84 mm). For a gypsum board sheathed ceiling, the diaphragm length shall be in accordance with Table R804.3.7.1. For a wood structural panel sheathed ceiling, the diaphragm length shall be not less than 12 feet (3658 mm) for building widths less than 36 feet (10 973 mm), or not less than 14 feet (4267 mm) for building widths greater than or equal to 36 feet (10 973 mm).
The ceiling diaphragm shall be secured with screws spaced at a maximum 6 inches (152 mm) o.c. at panel edges and a maximum 12 inches (305 mm) o.c. in the field. The required lengths in Table R804.3.7.1 for gypsum board sheathed ceiling diaphragms shall be permitted to be multiplied by 0.35 if all panel edges are blocked. Multiplying the required lengths in Table R804.3.7.1 for gypsum board sheathed ceiling diaphragms by 0.9 shall be permitted if all panel edges are secured with screws spaced at 4 inches (102 mm) o.c.
2025 CALIFORNIA RESIDENTIAL CODE 8-41
CRC § 2508.4 High relevance — show source text
2508.4 Adhesives. Gypsum panel products secured to framing with adhesives in ceiling assemblies shall be attached using an approved fastening schedule. Expandable foam adhesives for fastening gypsum wallboard shall conform to ASTM D6464. Other adhesives for the installation of gypsum wallboard shall conform to ASTM C557.
2508.5 Joint treatment. Gypsum panel product fire-resistance-rated assemblies shall have joints and fasteners treated.
Exceptions: Joint and fastener treatment need not be provided where any of the following conditions occur:
- Where the gypsum panel product is to receive a decorative finish such as wood paneling, battens, acoustical finishes or any similar application that would be equivalent to joint treatment.
- On single-layer systems where joints occur over wood framing members.
- Square edge or tongue-and-groove edge gypsum board (V-edge), gypsum panel products, gypsum backing board or gypsum sheathing.
- On multilayer systems where the joints of adjacent layers are offset.
- Assemblies tested without joint treatment.
2508.6 Horizontal gypsum panel product diaphragm ceilings. Gypsum panel products shall be permitted to be used on wood joists to create a horizontal diaphragm ceiling in accordance with Table 2508.6.
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GYPSUM PANEL PRODUCTS AND PLASTER
TABLE 2508.6—SHEAR CAPACITY FOR HORIZONTAL WOOD-FRAME GYPSUM PANEL PRODUCT DIAPHRAGM CEILING ASSEMBLIES Col2 Col3 Col4 Col5 MATERIAL THICKNESS OF
MATERIAL
(MINIMUM) (inches)SPACING OF
FRAMING MEMBERS
(inches)SHEAR VALUEa, b
(PLF OF CEILING)MIMIMUM FASTENER SIZE Gypsum panel product 1/2 16 o.c. 90 5d cooler or wallboard nail; 15/8-inch
long; 0.086-inch shank;15/64-inch headcGypsum panel product 1/2 24 o.c. 70 5d cooler or wallboard nail; 15/8-inch
long; 0.086-inch shank;15/64-inch headcFor SI: 1 inch = 25.4 mm, 1 pound per foot = 14.59 N/m.
a. Values are not cumulative with other horizontal diaphragm values and are for short-term wind or seismic loading. Values shall be reduced 25 percent for normal loading.
b. Values shall be reduced 50 percent in Seismic Design Categories D, E and F.
c. 11/4-inch, No. 6 Type S or W screws are permitted to be substituted for the listed nails.For SI: 1 inch = 25.4 mm, 1 pound per foot = 14.59 N/m.
a. Values are not cumulative with other horizontal diaphragm values and are for short-term wind or seismic loading. Values shall be reduced 25 percent for normal loading.
b. Values shall be reduced 50 percent in Seismic Design Categories D, E and F.
c. 11/4-inch, No.CRC § 25.4 High relevance — show source text
Values are not cumulative with other horizontal diaphragm values and are for short-term wind or seismic loading. Values shall be reduced 25 percent for normal loading.
b. Values shall be reduced 50 percent in Seismic Design Categories D, E and F.
c. 11/4-inch, No. 6 Type S or W screws are permitted to be substituted for the listed nails.|For SI: 1 inch = 25.4 mm, 1 pound per foot = 14.59 N/m.
a. Values are not cumulative with other horizontal diaphragm values and are for short-term wind or seismic loading. Values shall be reduced 25 percent for normal loading.
b. Values shall be reduced 50 percent in Seismic Design Categories D, E and F.
c. 11/4-inch, No. 6 Type S or W screws are permitted to be substituted for the listed nails.|2508.6.1 Diaphragm proportions. The maximum allowable diaphragm proportions shall be 1 [1] / 2 :1 between shear resisting elements. Rotation or cantilever conditions shall not be permitted.
2508.6.2 Installation. Gypsum panel products used in a horizontal diaphragm ceiling shall be installed perpendicular to ceiling framing members. End joints of adjacent courses of gypsum board shall not occur on the same joist.
2508.6.3 Blocking of perimeter edges. Perimeter edges shall be blocked using a wood member not less than 2-inch by 6-inch (51 mm by 152 mm) nominal dimension. Blocking material shall be installed flat over the top plate of the wall to provide a nailing surface not less than 2 inches (51 mm) in width for the attachment of the gypsum panel product.
2508.6.4 Fasteners. Fasteners used for the attachment of gypsum panel products to a horizontal diaphragm ceiling shall be as defined in Table 2508.6. Fasteners shall be spaced not more than 7 inches (178 mm) on center at all supports, including perimeter blocking, and not more than [3] / 8 inch (9.5 mm) from the edges and ends of the gypsum panel product.
2508.6.5 Lateral force restrictions. Gypsum panel products shall not be used in diaphragm ceilings to resist lateral forces imposed by masonry or concrete construction.
2508.6.6 Diaphragm ceiling connection to partitions. [DSA-SS & DSA-SS/CC and OSHPD 1, 1R, 2, 4 & 5] Gypsum board shall not be used in diaphragm ceilings to resist lateral forces imposed by partitions. Connection of diaphragm ceiling to the vertical lateral force resisting elements shall be designed and detailed to transfer lateral forces.
Exception: [OSHPD 2] Single-story Type V skilled nursing or intermediate care facilities utilizing wood-frame or light-steel-frame construction.
SECTION 2509—SHOWERS AND WATER CLOSETS
2509.1 Wet areas. Showers and public toilet walls shall conform to Section 1210.2.
CRC § 0.35 High relevance — show source text
Ceiling diaphragm is composed of1/2-inch gypsum board (min. thickness) secured with screws spaced at 6 inches o.c. at panel edges and 12 inches o.c. infield. Use No. 8
screws (min.) where framing members have a designation thickness of 54 mils or less and No. 10 screws (min.) where framing members have a designation thickness greater
than 54 mils.
b. Maximum aspect ratio (length/width) of diaphragms is 2:1.
c. Building width is in the direction of horizontal framing members supported by the wall studs.
d. Required diaphragm lengths are to be provided at each end of the structure.
e. Multiplying required diaphragm lengths by 0.35 is permitted if all panel edges are blocked.
f. Multiplying required diaphragm lengths by 0.9 is permitted if all panel edges are secured with screws spaced at 4 inches o.c.
g. To determine the minimum diaphragm length for buildings with ceiling heights of 9 feet or 10 feet values in this table shall be multiplied by 1.15.|FIGURE R804.3.7.1(1)—CEILING DIAPHRAGM TO GABLE ENDWALL DETAIL
CEILING JOISTS
FLAT STUD OR TRACK BLOCKING AT 48 IN. O.C. AT FIRST TWO JOIST SPACES
3 NO. 8 SCREWS AT EACH STUD
STUD BLOCKING AT CEILING ELEVATION
GABLE
ENDWALL
STUDS
For SI: 1 inch = 25.4 mm.
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FIGURE R804.3.7.1(2)—CEILING DIAPHRAGM TO SIDEWALL DETAIL
ROOF-CEILING CONSTRUCTION
ROOF RAFTER (OR TRUSS TOP CHORD)
CEILING JOIST (OR TRUSS BOTTOM CHORD)
WOOD STRUCTURAL
PANEL OR GYPSUM
BOARD DIAPHRAGM
350T125-33 TRACK
ROOF SHEATHING
ROOF BLOCKING
NO. 8 SCREWS AT 6 IN. O.C.
STRUCTURAL WALL
For SI: 1 inch = 25.4 mm.
R804.3.7.2 Roof diaphragm. A roof diaphragm shall be provided by attaching not less than [3] / 8 -inch (9.5 mm) wood structural panel that complies with Section R803 to roof rafters or truss top chords in accordance with Table R804.3. Buildings with 3:1 or larger plan aspect ratio and with roof rafter slope (pitch) of 9:12 or larger shall have the roof rafters and ceiling joists blocked in accordance with Figure R804.3.7.2.
FIGURE R804.3.7.2—ROOF BLOCKING DETAIL
BE ATTACHED TO OUTSIDE FACE OF SHEATHING OR PREFERABLY DIRECTLY TO TRACK FLANGE PRIOR TO SHEATHING PLACEMENT AS SHOWN
For SI: 1 mil = 0.0254 mm, 1 inch = 25.4 mm, 1 foot = 304.8 mm.
2025 CALIFORNIA RESIDENTIAL CODE 8-43
CRC § 1.15. High relevance — show source text
To determine the minimum diaphragm length for buildings with ceiling heights of 9 feet or 10 feet values in this table shall be multiplied by 1.15.|For SI: 1 inch = 25.4 mm, 1 mile per hour = 0.447 m/s, 1 foot = 304.8 mm, 1 mil = 0.0254 mm.
a. Ceiling diaphragm is composed of1/2-inch gypsum board (min. thickness) secured with screws spaced at 6 inches o.c. at panel edges and 12 inches o.c. infield. Use No. 8
screws (min.) where framing members have a designation thickness of 54 mils or less and No. 10 screws (min.) where framing members have a designation thickness greater
than 54 mils.
b. Maximum aspect ratio (length/width) of diaphragms is 2:1.
c. Building width is in the direction of horizontal framing members supported by the wall studs.
d. Required diaphragm lengths are to be provided at each end of the structure.
e. Multiplying required diaphragm lengths by 0.35 is permitted if all panel edges are blocked.
f. Multiplying required diaphragm lengths by 0.9 is permitted if all panel edges are secured with screws spaced at 4 inches o.c.
g. To determine the minimum diaphragm length for buildings with ceiling heights of 9 feet or 10 feet values in this table shall be multiplied by 1.15.|For SI: 1 inch = 25.4 mm, 1 mile per hour = 0.447 m/s, 1 foot = 304.8 mm, 1 mil = 0.0254 mm.
a. Ceiling diaphragm is composed of1/2-inch gypsum board (min. thickness) secured with screws spaced at 6 inches o.c. at panel edges and 12 inches o.c. infield. Use No. 8
screws (min.) where framing members have a designation thickness of 54 mils or less and No. 10 screws (min.) where framing members have a designation thickness greater
than 54 mils.
b. Maximum aspect ratio (length/width) of diaphragms is 2:1.
c. Building width is in the direction of horizontal framing members supported by the wall studs.
d. Required diaphragm lengths are to be provided at each end of the structure.
e. Multiplying required diaphragm lengths by 0.35 is permitted if all panel edges are blocked.
f. Multiplying required diaphragm lengths by 0.9 is permitted if all panel edges are secured with screws spaced at 4 inches o.c.
g. To determine the minimum diaphragm length for buildings with ceiling heights of 9 feet or 10 feet values in this table shall be multiplied by 1.15.|For SI: 1 inch = 25.4 mm, 1 mile per hour = 0.447 m/s, 1 foot = 304.8 mm, 1 mil = 0.0254 mm.
a. Ceiling diaphragm is composed of1/2-inch gypsum board (min. thickness) secured with screws spaced at 6 inches o.c. at panel edges and 12 inches o.c. infield. Use No. 8
screws (min.) where framing members have a designation thickness of 54 mils or less and No. 10 screws (min.)CRC § 2508.6.3 High relevance — show source text
2508.6.3 Blocking of perimeter edges. Perimeter edges shall be blocked using a wood member not less than 2-inch by 6-inch (51 mm by 152 mm) nominal dimension. Blocking material shall be installed flat over the top plate of the wall to provide a nailing surface not less than 2 inches (51 mm) in width for the attachment of the gypsum panel product.
2508.6.4 Fasteners. Fasteners used for the attachment of gypsum panel products to a horizontal diaphragm ceiling shall be as defined in Table 2508.6. Fasteners shall be spaced not more than 7 inches (178 mm) on center at all supports, including perimeter blocking, and not more than [3] / 8 inch (9.5 mm) from the edges and ends of the gypsum panel product.
2508.6.5 Lateral force restrictions. Gypsum panel products shall not be used in diaphragm ceilings to resist lateral forces imposed by masonry or concrete construction.
2508.6.6 Diaphragm ceiling connection to partitions. [DSA-SS & DSA-SS/CC and OSHPD 1, 1R, 2, 4 & 5] Gypsum board shall not be used in diaphragm ceilings to resist lateral forces imposed by partitions. Connection of diaphragm ceiling to the vertical lateral force resisting elements shall be designed and detailed to transfer lateral forces.
Exception: [OSHPD 2] Single-story Type V skilled nursing or intermediate care facilities utilizing wood-frame or light-steel-frame construction.
SECTION 2509—SHOWERS AND WATER CLOSETS
2509.1 Wet areas. Showers and public toilet walls shall conform to Section 1210.2.
2509.2 Base for tile. Materials used as a base for wall tile in tub and shower areas and wall and ceiling panels in shower areas shall be of materials listed in Table 2509.2 and installed in accordance with the manufacturer’s recommendations. Water-resistant gypsum backing board shall be used as a base for tile in water closet compartment walls when installed in accordance with GA-216 or ASTM C840 and the manufacturer’s recommendations. Regular gypsum wallboard is permitted under tile or wall panels in other wall and ceiling areas when installed in accordance with GA 216 or ASTM C840.
TABLE 2509.2—BACKERBOARD MATERIALS Col2 MATERIAL STANDARD Glass mat gypsum backing panel ASTM C1178 Nonasbestos fiber-cement backer board ASTM C1288 or ISO 8336, Category C Fiber-mat reinforced cementitious backer unit ASTM C1325 2509.3 Limitations. Water-resistant gypsum backing board shall not be used in the following locations:
- Over a vapor retarder in shower or bathtub compartments.
- Where there will be direct exposure to water or in areas subject to continuous high humidity.
SECTION 2510—LATHING AND FURRING FOR CEMENT PLASTER (STUCCO)
2510.1 General. Exterior and interior cement plaster and lathing shall be done with the appropriate materials listed in Table 2507.2 and Chapter 35.
2510.2 Weather protection. Materials shall be stored in such a manner as to protect them from the weather.
2510.3 Installation. Installation of these materials shall be in compliance with ASTM C926 and ASTM C1063.
CRC § 2508.1 High relevance — show source text
SECTION 2508—GYPSUM CONSTRUCTION
2508.1 General. Gypsum panel products and gypsum plaster construction shall be of the materials listed in Tables 2506.2 and 2507.2. These materials shall be assembled and installed in compliance with the appropriate standards listed in Tables 2508.1 and 2511.1.1 and Chapter 35.
TABLE 2508.1—INSTALLATION OF GYPSUM CONSTRUCTION Col2 MATERIAL STANDARD Gypsum panel products GA-216; ASTM C840 Gypsum sheathing and gypsum panel products ASTM C1280; GA-253 Gypsum veneer base ASTM C844 Interior lathing and furring ASTM C841 Steel framing for gypsum panel products ASTM C754; C1007 2508.2 Limitations. Gypsum wallboard or gypsum plaster shall not be used in any exterior surface where such gypsum construction will be exposed directly to the weather. Gypsum wallboard shall not be used where there will be direct exposure to water or continuous high humidity conditions. Gypsum sheathing shall be installed on exterior surfaces in accordance with ASTM C1280 or GA-253.
2508.2.1 Weather protection. Gypsum wallboard, gypsum lath or gypsum plaster shall not be installed until weather protection for the installation is provided.
2508.3 Single-ply application. Edges and ends of gypsum panel products shall occur on the framing members, except those edges and ends that are perpendicular to the framing members. Edges and ends of gypsum panel products shall be in moderate contact except in concealed spaces where fire-resistance-rated construction, shear resistance or diaphragm action is not required.
2508.3.1 Floating angles. Fasteners at the top and bottom plates of vertical assemblies, or the edges and ends of horizontal assemblies perpendicular to supports, and at the wall line are permitted to be omitted except on shear resisting elements or fireresistance-rated assemblies. Fasteners shall be applied in such a manner as not to fracture the face paper with the fastener head.
2508.4 Adhesives. Gypsum panel products secured to framing with adhesives in ceiling assemblies shall be attached using an approved fastening schedule. Expandable foam adhesives for fastening gypsum wallboard shall conform to ASTM D6464. Other adhesives for the installation of gypsum wallboard shall conform to ASTM C557.
2508.5 Joint treatment. Gypsum panel product fire-resistance-rated assemblies shall have joints and fasteners treated.
Exceptions: Joint and fastener treatment need not be provided where any of the following conditions occur:
- Where the gypsum panel product is to receive a decorative finish such as wood paneling, battens, acoustical finishes or any similar application that would be equivalent to joint treatment.
- On single-layer systems where joints occur over wood framing members.
- Square edge or tongue-and-groove edge gypsum board (V-edge), gypsum panel products, gypsum backing board or gypsum sheathing.
- On multilayer systems where the joints of adjacent layers are offset.
- Assemblies tested without joint treatment.
2508.6 Horizontal gypsum panel product diaphragm ceilings. Gypsum panel products shall be permitted to be used on wood joists to create a horizontal diaphragm ceiling in accordance with Table 2508.6.
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CRC § 0.35 High relevance — show source text
Required diaphragm lengths are to be provided at each end of the structure.
e. Multiplying required diaphragm lengths by 0.35 is permitted if all panel edges are blocked.
f. Multiplying required diaphragm lengths by 0.9 is permitted if all panel edges are secured with screws spaced at 4 inches o.c.
g. To determine the minimum diaphragm length for buildings with ceiling heights of 9 feet or 10 feet values in this table shall be multiplied by 1.15.|For SI: 1 inch = 25.4 mm, 1 mile per hour = 0.447 m/s, 1 foot = 304.8 mm, 1 mil = 0.0254 mm.
a. Ceiling diaphragm is composed of1/2-inch gypsum board (min. thickness) secured with screws spaced at 6 inches o.c. at panel edges and 12 inches o.c. infield. Use No. 8
screws (min.) where framing members have a designation thickness of 54 mils or less and No. 10 screws (min.) where framing members have a designation thickness greater
than 54 mils.
b. Maximum aspect ratio (length/width) of diaphragms is 2:1.
c. Building width is in the direction of horizontal framing members supported by the wall studs.
d. Required diaphragm lengths are to be provided at each end of the structure.
e. Multiplying required diaphragm lengths by 0.35 is permitted if all panel edges are blocked.
f. Multiplying required diaphragm lengths by 0.9 is permitted if all panel edges are secured with screws spaced at 4 inches o.c.
g. To determine the minimum diaphragm length for buildings with ceiling heights of 9 feet or 10 feet values in this table shall be multiplied by 1.15.|For SI: 1 inch = 25.4 mm, 1 mile per hour = 0.447 m/s, 1 foot = 304.8 mm, 1 mil = 0.0254 mm.
a. Ceiling diaphragm is composed of1/2-inch gypsum board (min. thickness) secured with screws spaced at 6 inches o.c. at panel edges and 12 inches o.c. infield. Use No. 8
screws (min.) where framing members have a designation thickness of 54 mils or less and No. 10 screws (min.) where framing members have a designation thickness greater
than 54 mils.
b. Maximum aspect ratio (length/width) of diaphragms is 2:1.
c. Building width is in the direction of horizontal framing members supported by the wall studs.
d. Required diaphragm lengths are to be provided at each end of the structure.
e. Multiplying required diaphragm lengths by 0.35 is permitted if all panel edges are blocked.
f. Multiplying required diaphragm lengths by 0.9 is permitted if all panel edges are secured with screws spaced at 4 inches o.c.
g. To determine the minimum diaphragm length for buildings with ceiling heights of 9 feet or 10 feet values in this table shall be multiplied by 1.15.|For SI: 1 inch = 25.4 mm, 1 mile per hour = 0.447 m/s, 1 foot = 304.8 mm, 1 mil = 0.0254 mm.
a.CRC § 3.6 High relevance — show source text
R702.3.6 Horizontal gypsum board diaphragm ceilings. Gypsum board and gypsum panel products shall be permitted on wood joists to create a horizontal diaphragm in accordance with Table R702.3.6. Gypsum board and gypsum panel products shall be
7-6 2025 CALIFORNIA RESIDENTIAL CODE
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WALL COVERING
installed perpendicular to ceiling framing members. End joints of adjacent courses of board and panels shall not occur on the same joist. The maximum allowable diaphragm proportions shall be 1 [1] / 2 :1 between shear resisting elements. Rotation or cantilever conditions shall not be permitted. Gypsum board or gypsum panel products shall not be used in diaphragm ceilings to resist lateral forces imposed by masonry or concrete construction. Perimeter edges shall be blocked using wood members not less than 2-inch by 6-inch (51 mm by 152 mm) nominal dimension. Blocking material shall be installed flat over the top plate of the wall to provide a nailing surface not less than 2 inches (51 mm) in width for the attachment of the gypsum board or gypsum panel product.
TABLE R702.3.6—SHEAR CAPACITY FOR HORIZONTAL WOOD-FRAMED GYPSUM BOARD DIAPHRAGM CEILING ASSEMBLIES Col2 Col3 Col4 Col5 ** MATERIAL** ** THICKNESS OF**
MATERIAL (min.) (inch)** SPACING OF FRAMING**
MEMBERS (max.) (inch)** SHEAR VALUEa, b
(plf of ceiling)**** MINIMUM FASTENER SIZEc, d** Gypsum board or gypsum
panel product1/2 16 o.c. 90 5d cooler or wallboard nail;
15/8-inch long; 0.086-inch shank;
15/64-inch headGypsum board or gypsum
panel product1/2 24 o.c. 70 5d cooler or wallboard nail;
15/8-inch long; 0.086-inch shank;
15/64-inch headFor SI: 1 inch = 25.4 mm, 1 pound per linear foot = 1.488 kg/m.
a. Values are not cumulative with other horizontal diaphragm values and are for short-term loading caused by wind or seismic loading. Values shall be reduced 25 percent for
normal loading.
b. Values shall be reduced 50 percent in Seismic Design Categories D0, D1, D2 and E.
c. 11/4-inch, No. 6 Type S or W screws shall be permitted to be substituted for the listed nails.
d. Fasteners shall be spaced not more than 7 inches on center at all supports, including perimeter blocking, and not less than3/8 inch from the edges and ends of the gypsum
board.For SI: 1 inch = 25.4 mm, 1 pound per linear foot = 1.488 kg/m.
a. Values are not cumulative with other horizontal diaphragm values and are for short-term loading caused by wind or seismic loading. Values shall be reduced 25 percent for
normal loading.
b. Values shall be reduced 50 percent in Seismic Design Categories D0, D1, D2 and E.
c. 11/4-inch, No.CRC § 0.84 High relevance — show source text
Flat blocking shall consist of C-shaped or track section with a minimum thickness of 33 mils (0.84 mm). For a gypsum board sheathed ceiling, the diaphragm length shall be in accordance with Table R804.3.7.1. For a wood structural panel sheathed ceiling, the diaphragm length shall be not less than 12 feet (3658 mm) for building widths less than 36 feet (10 973 mm), or not less than 14 feet (4267 mm) for building widths greater than or equal to 36 feet (10 973 mm).
The ceiling diaphragm shall be secured with screws spaced at a maximum 6 inches (152 mm) o.c. at panel edges and a maximum 12 inches (305 mm) o.c. in the field. The required lengths in Table R804.3.7.1 for gypsum board sheathed ceiling diaphragms shall be permitted to be multiplied by 0.35 if all panel edges are blocked. Multiplying the required lengths in Table R804.3.7.1 for gypsum board sheathed ceiling diaphragms by 0.9 shall be permitted if all panel edges are secured with screws spaced at 4 inches (102 mm) o.c.
2025 CALIFORNIA RESIDENTIAL CODE 8-41
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ROOF-CEILING CONSTRUCTION
TABLE R804.3.7.1—REQUIRED LENGTHS FOR CEILING DIAPHRAGMS AT
GABLE ENDWALLS GYPSUM BOARD SHEATHED, CEILING HEIGHT = 8 FEETa, b, c, d, e, f, gCol2 Col3 Col4 Col5 Col6 Col7 Col8 ** EXPOSURE CATEGORY** ** EXPOSURE CATEGORY** ** ULTIMATE DESIGN WIND SPEED (mph)** ** ULTIMATE DESIGN WIND SPEED (mph)** ** ULTIMATE DESIGN WIND SPEED (mph)** ** ULTIMATE DESIGN WIND SPEED (mph)** ** ULTIMATE DESIGN WIND SPEED (mph)** ** ULTIMATE DESIGN WIND SPEED (mph)** ** B** ** B** ** 115** ** 120** ** 130** ** < 140** ** —** ** —** ** C** ** C** ** —** ** —** ** 115** ** 120** ** 130** ** < 140** ** Roof pitch** ** Building endwall width**
(feet)** Minimum diaphragm length**
(feet)** Minimum diaphragm length**
(feet)** Minimum diaphragm length**
(feet)** Minimum diaphragm length**
(feet)3:12 to 6:12 24–28 16 18 24 26 30 34 3:12 to 6:12 > 28–32 20 20 26 32 34 40 3:12 to 6:12 > 32–36 24 26 30 36 42 46 3:12 to 6:12 > 36–40 26 28 36 40 48 52 6:12 to 9:12 > CRC § 3.5.1 High relevance — show source text
Three-eighths-inch-thick single-ply gypsum board or gypsum panel product 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 or gypsum panel
product shall be applied perpendicular to framing. Where applying a water-based texture material, the minimum gypsum board thickness shall be increased from3/8 inch to1/2 inch
for 16-inch on center framing, and from1/2 inch to5/8 inch for 24-inch on center framing or1/2-inch sag-resistant gypsum ceiling board shall be used.|R702.3.5.1 Screw fastening. Screws for attaching gypsum board and gypsum panel products to wood framing shall be Type W or Type S in accordance with ASTM C1002 and shall penetrate the wood not less than [5] / 8 inch (15.9 mm). Gypsum board and gypsum panel products shall be attached to cold-formed steel framing with minimum No. 6 screws. Screws for attaching gypsum board and gypsum panel products to cold-formed steel framing less than 0.033 inch (1 mm) thick shall be Type S in accordance with ASTM C1002 or bugle head style in accordance with ASTM C1513 and shall penetrate the steel not less than [3] / 8 inch (9.5 mm). Screws for attaching gypsum board and gypsum panel products to cold-formed steel framing 0.033 inch to 0.112 inch (1 mm to 3 mm) thick shall be in accordance with ASTM C954 or bugle head style in accordance with ASTM C1513. Screws for attaching gypsum board and gypsum panel products to structural insulated panels shall penetrate the wood structural panel facing not less than [7] / 16 inch (11.1 mm).
R702.3.6 Horizontal gypsum board diaphragm ceilings. Gypsum board and gypsum panel products shall be permitted on wood joists to create a horizontal diaphragm in accordance with Table R702.3.6. Gypsum board and gypsum panel products shall be
7-6 2025 CALIFORNIA RESIDENTIAL CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
WALL COVERING
installed perpendicular to ceiling framing members. End joints of adjacent courses of board and panels shall not occur on the same joist. The maximum allowable diaphragm proportions shall be 1 [1] / 2 :1 between shear resisting elements. Rotation or cantilever conditions shall not be permitted. Gypsum board or gypsum panel products shall not be used in diaphragm ceilings to resist lateral forces imposed by masonry or concrete construction. Perimeter edges shall be blocked using wood members not less than 2-inch by 6-inch (51 mm by 152 mm) nominal dimension. Blocking material shall be installed flat over the top plate of the wall to provide a nailing surface not less than 2 inches (51 mm) in width for the attachment of the gypsum board or gypsum panel product.
TABLE R702.3.6—SHEAR CAPACITY FOR HORIZONTAL WOOD-FRAMED GYPSUM BOARD DIAPHRAGM CEILING ASSEMBLIES Col2 Col3 Col4 Col5 ** MATERIAL** ** THICKNESS OF**
MATERIAL (min.) (inch)** SPACING OF FRAMING**
**MEMBERS (max.)
Frequently asked questions
What minimum gypsum thickness is required to use gypsum as a horizontal ceiling diaphragm?
Gypsum board used as a horizontal diaphragm must meet the minimum material thickness in Table R702.3.6 (typically 1/2 in. for the standard diaphragm entries) and be installed perpendicular to framing with blocked perimeter edges as required by §R702.3.6.
What fastener type and spacing does the CRC require for gypsum ceiling diaphragms?
The CRC requires approved screw/nail types and penetration per §R702.3.5.1 for attachment; ceiling diaphragms are secured with screws spaced a maximum 6 inches o.c. at panel edges and 12 inches o.c. in the field (with No. 8 or No. 10 screws as specified by framing thickness) per the roof/ceiling diaphragm provisions.
Can 3/8‑inch gypsum board be used on ceilings?
Single‑ply 3/8‑inch gypsum board is not permitted on ceilings where water‑based textured finishes will be applied or where it must support insulation — the code requires increased thickness or sag‑resistant ceiling board in those cases (see the gypsum fastening and texture limitations in §R702.3.5.1).
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