CRC · California Residential Code

What fastener patterns and blocking are required for ceiling diaphragms (seismic/diaphragm continuity)?

For a homeowner: the CRC requires that ceiling diaphragms at gable endwalls be made of specific ceiling panels, attached with screws at the code edge/field spacings, and tied into the wall with blocking and a minimum length (from a code table) so the wall is properly braced in wind and earthquake — installers must follow **§ R804.3.7.1** and **§ R804.3.7.2** and document the blocking and fastener pattern.

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

The California Residential Code requires that a ceiling diaphragm at gable endwalls be constructed of either 1/2‑inch gypsum board or 3/8‑inch wood structural panel, be connected to the wall framing per the detail, and be fastened and blocked per § R804.3.7.1 (ceiling diaphragms) and § R804.3.7.2 (roof diaphragm blocking). The code specifies the fastener pattern (edge and field spacings and minimum screw sizes), the blocking type and size, and the minimum diaphragm lengths (Table R804.3.7.1), with permitted multipliers when edges are blocked or fastened at closer spacing. The controlling text is in § R804.3.7.1 and § R804.3.7.2 (see cited code excerpts).

The single most important plain‑English rule: secure the diaphragm to joists/trusses with the required screws at the code edge and field spacings, provide the required blocking at the wall line (or the specified track/flat blocking), and use the table/multipliers in § R804.3.7.1 to determine how far the diaphragm must extend toward the roof to properly tie the gable endwall.

Requirements in detail

Key definitions / thresholds (first mention bolded)

  • Ceiling diaphragm — the horizontal diaphragm formed by ceiling sheathing at the bottom of ceiling joists or truss bottom chords (see § R804.3.7.1).
  • Flat blocking — C‑shaped or track section minimum thickness 33 mils (0.84 mm) when used as the flat blocking specified in the gable‑end details. § R804.3.7.1.
  • Perimeter blocking (gypsum ceilings) — wood blocking not less than 2 in. × 6 in. nominal installed flat over the top plate where required by R702.3.6.
  • Maximum edge fastener spacing: 6 inches o.c. at panel edges (gypsum board ceiling default). Maximum field spacing: 12 inches o.c. in the field. § R804.3.7.1.
  • Minimum screw sizes: No. 8 screws (min.) where framing members have a designation thickness of 54 mils or less; No. 10 screws (min.) where framing members are thicker than 54 mils (this note applies to the gypsum board ceiling diaphragm description tied to Table R804.3.7.1).
  • Aspect ratio limit: maximum diaphragm length/width = 2:1 (limits applicability of the table).

Fastener pattern (what to install)

  • For a gypsum board sheathed ceiling (the typical case in Table R804.3.7.1):
    • Use at minimum 1/2‑inch gypsum board installed perpendicular to framing members.
    • Fasten with screws spaced not more than 6 inches o.c. at panel edges and not more than 12 inches o.c. in the field. § R804.3.7.1.
    • Use No. 8 screws minimum for thinner framing (≤54 mils) or No. 10 screws minimum for heavier framing (>54 mils).
  • For wood structural panel sheathed ceilings: the code gives minimum diaphragm lengths (see next table) and requires sheathing that complies with Section R803; fastening details for wood panel diaphragms follow the applicable sheathing schedules and table guidance referenced in the code.

Blocking (what and where)

  • Flat blocking at gable endwalls: C‑shaped or track section, minimum 33 mils thickness, installed as shown in the gable detail of § R804.3.7.1 (see Figure R804.3.7.1).
  • Perimeter blocking for gypsum ceilings: wood member not less than 2" × 6" nominal installed flat over top plate to provide at least 2 inches of nailing surface for gypsum panels (R702.3.6).
  • The gable‑end detail also illustrates blocking at the first two joist spaces at 48 in. o.c. and 3 No. 8 screws at each stud where shown — follow the figure callouts for placement at gable endwalls.

Diaphragm length and multipliers (how far the diaphragm must extend)

  • For gypsum‑sheathed ceilings, use Table R804.3.7.1 to determine the minimum diaphragm length required at gable endwalls. Values depend on roof pitch, building endwall width, exposure, and ultimate design wind speed. § R804.3.7.1.
  • For wood structural panel sheathed ceilings, the minimum diaphragm length is not less than 12 feet for building widths < 36 feet, or not less than 14 feet for building widths ≥ 36 feet. § R804.3.7.1.
  • Permitted multipliers for gypsum board diaphragms (Table R804.3.7.1 notes):
    • Multiply required Table lengths by 0.35 if all panel edges are blocked.
    • Multiply required Table lengths by 0.9 if all panel edges are secured with screws at 4 inches o.c. (i.e., closer edge screw spacing).

Decision‑relevant summary table

Item Code value / dimension Code Reference
Ceiling sheathing (gypsum) 1/2 in. gypsum board (min) § R804.3.7.1
Ceiling sheathing (wood panel) 3/8 in. wood structural panel (min) § R804.3.7.1
Edge fastener spacing (gypsum) 6 in. o.c. max at panel edges § R804.3.7.1
Field fastener spacing (gypsum) 12 in. o.c. max in field § R804.3.7.1
Minimum screw sizes No. 8 (≤54 mils framing) / No. 10 (>54 mils framing) Table note to R804.3.7.1
Flat blocking type & thickness C‑shaped or track, min 33 mils § R804.3.7.1
Perimeter blocking (gypsum) Wood member 2"×6" nominal installed flat § R702.3.6
Wood panel diaphragm minimum length 12 ft (<36 ft width) or 14 ft (≥36 ft width) § R804.3.7.1
Gypsum diaphragm lengths See Table R804.3.7.1 (varies by pitch, width, exposure, Vult) § R804.3.7.1
Multipliers for gypsum table lengths ×0.35 if all edges blocked; ×0.9 if edges screwed at 4 in. o.c. Table notes to R804.3.7.1
Aspect ratio limit Max diaphragm length/width = 2:1 Table notes / R804.3.7.1 notes
Roof diaphragm blocking (special cases) Buildings with plan aspect ratio ≥ 3:1 and roof pitch ≥ 9:12 require blocking per figure § R804.3.7.2

Notes on fastener type

  • The code prescribes screws for securing gypsum ceiling diaphragms in the R804.3.7.1 description (edge/field patterns). Use corrosion‑resistant fasteners where required and the screw sizes noted above.
  • For gypsum diaphragm shear capacity and alternative fasteners the R702.3.6 table and notes provide minimum fastener sizing and spacing for diaphragm shear values; consult § R702.3.6 when designing shear capacity.

Exceptions & special cases

  • The code allows reduction of required Table lengths under two conditions: (1) all panel edges are blocked (×0.35), or (2) all panel edges are fastened at 4 in. o.c. (×0.9). Apply these only to the gypsum board values in Table R804.3.7.1. § R804.3.7.1.
  • Wood structural panel ceilings use the fixed minima (12 ft or 14 ft) rather than Table R804.3.7.1 values. § R804.3.7.1.
  • Roof diaphragms and certain plan aspect ratios require additional blocking of rafters and ceiling joists per § R804.3.7.2 (buildings with plan aspect ratio 3:1 or larger and roof rafter slope ≥ 9:12).
  • Special inspection: in seismic design categories C–F some diaphragm fastening operations may require periodic or continuous special inspection per § 1705.13.2, with exceptions where edge spacing is > 4 in. o.c. (see that section).

Common mistakes

  • Assuming nails are acceptable for gypsum diaphragm edge fastening. The gypsum ceiling diaphragm description prescribes screws with specific sizes and spacings — follow § R804.3.7.1 and Table notes.
  • Forgetting to provide the required flat blocking (C‑section / track min 33 mils) at gable endwalls or the 2×6 perimeter blocking for gypsum ceilings. Both are code requirements in the respective sections.
  • Misapplying multipliers: the 0.35 and 0.9 multipliers apply only to the gypsum board values in Table R804.3.7.1, not to the wood‑panel minimums.
  • Ignoring the 2:1 aspect‑ratio limit for using Table values — if the diaphragm geometry exceeds that, the table may not apply.
  • Not verifying whether special inspection is required for diaphragm fastening in higher seismic design categories (see § 1705.13.2).

Worked example — applying the rule with numbers

Scenario: single‑story house with gable endwall. Ceiling type: 1/2‑inch gypsum board; ceiling height = 8 ft; building endwall width = 28 ft; roof pitch = 4:12 (within 3:12–6:12 row); Exposure B; ultimate design wind speed falls in the column that calls for a minimum diaphragm length = 18 ft in Table R804.3.7.1 (example table entries shown in the code). Use Table R804.3.7.1 to confirm the 18‑ft requirement for these inputs.

Steps:

  1. Provide the gypsum ceiling diaphragm and connect to the bottom of ceiling joists per the gable detail in § R804.3.7.1.
  2. Fasten the gypsum: screws at 6 in. o.c. at panel edges and 12 in. o.c. in the field; use No. 8 screws minimum if framing member thickness ≤ 54 mils (or No. 10 if thicker).
  3. Diaphragm length: the Table value is 18 ft at the gable endwall for this example (confirm with Table R804.3.7.1). That means the gypsum diaphragm must extend a minimum longitudinal distance of 18 ft from the gable wall along the roof/ceiling plane to develop the required load transfer.
  4. If you choose to block all panel edges, you may reduce the Table length by the ×0.35 multiplier: 18 ft × 0.35 = 6.3 ft. That is permitted by the Table note — but you must actually install continuous edge blocking per the code before applying the multiplier. § R804.3.7.1.
  5. If instead you keep edges unblocked but fasten all panel edges at 4 in. o.c., you can multiply the 18 ft by 0.9 → 16.2 ft minimum. § R804.3.7.1.

Round and document these values on the plans; if special inspection is triggered by the project seismic category or other code triggers, arrange for it per § 1705.13.2.

Related provisions

  • R702.3.6 — Horizontal gypsum board diaphragm ceilings (blocking and fastener tables/notes) — § R702.3.6.
  • Table R804.3.7.1 — Required lengths for ceiling diaphragms at gable endwalls (gypsum board sheathed) — § R804.3.7.1 (table and notes).
  • R804.3.7.2 — Roof diaphragm blocking detail (3:1 plan aspect ratio and steep roofs) — § R804.3.7.2.
  • 1705.13.2 — Special inspection requirements for structural wood (diaphragms) in certain seismic design categories — § 1705.13.2.

Important note about the requested controlling section § R804.3.1.4: I searched the provided CRC files but did not find the text for § R804.3.1.4 in the materials made available to me. I therefore grounded the article only on the retrieved sections (§ R804.3.7.1 and § R804.3.7.2) and the related provisions noted above. If you intended a different section number, or can upload the file/section that contains § R804.3.1.4, I will update the article and link its requirements explicitly.

Code references

Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:

  • 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

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    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, g    		 Col2 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 § 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.|

    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

  • CRC § 3.5 High relevance — show source text

    FIGURE R804.3.5(1)—ROOF OR CEILING OPENING

    For SI: 1 foot = 304.8 mm.

    8-40 2025 CALIFORNIA RESIDENTIAL CODE

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    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 § 25.4 High relevance — show source text

    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. 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. 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. 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. 6 Type S or W screws shall be permitted to be substituted for the listed nails.
    d.

  • 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.

    8-42 2025 CALIFORNIA RESIDENTIAL CODE

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    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 § 4.00 High relevance — show source text

    10
    wood screw|1|24|4.00|0.90|DR|DR|2.85|DR|DR|DR| |Minimum 1x
    Wood Furringd|Minimum 2x
    Wood Stud|1/4" lag screw|11/2|12|4.00|2.65|1.50|0.90|4.00|1.65|0.80|DR| |Minimum 1x
    Wood Furringd|Minimum 2x
    Wood Stud|1/4" lag screw|11/2|16|4.00|1.95|0.95|0.50|4.00|1.10|DR|DR| |Minimum 1x
    Wood Furringd|Minimum 2x
    Wood Stud|1/4" lag screw|11/2|24|4.00|1.10|DR|DR|3.25|0.50|DR|DR| |For SI: 1 inch = 25.4 mm, 1 pound per square foot (psf) = 0.0479 kPa, 1 pound per square inch = 0.00689 MPa.
    DR = Design Required, o.c. = on center.
    a. Wood framing and furring shall be spruce-pine-fir or any wood species with a specific gravity of 0.42 or greater in accordance with ANSI/AWC NDS.
    b. Nail fasteners shall comply with ASTM F1667, except nail length shall be permitted to exceed ASTM F1667 standard lengths.
    c. The thickness of wood structural panels complying with the specific gravity requirements of Note a shall be permitted to be included in satisfying the minimum required
    penetration into framing.
    d. Where the required cladding fastener penetration into wood material exceeds3/4 inch and is not more than 11/2 inches, a minimum 2-inch nominal wood furring or an
    approved design shall be used.
    e. Foam sheathing shall have a minimum compressive strength of 15 psi in accordance with ASTM C578 or ASTM C1289.
    f. Furring shall be spaced not greater than 24 inches on center in a vertical or horizontal orientation. In a vertical orientation, furring shall be located over wall studs and attached with
    the required fastener spacing. In a horizontal orientation, the indicated 8-inch and 12-inch fastener spacing in furring shall be achieved by use of two fasteners into studs at 16 inches
    and 24 inches on center, respectively.|For SI: 1 inch = 25.4 mm, 1 pound per square foot (psf) = 0.0479 kPa, 1 pound per square inch = 0.00689 MPa.
    DR = Design Required, o.c. = on center.
    a. Wood framing and furring shall be spruce-pine-fir or any wood species with a specific gravity of 0.42 or greater in accordance with ANSI/AWC NDS.
    b. Nail fasteners shall comply with ASTM F1667, except nail length shall be permitted to exceed ASTM F1667 standard lengths.
    c. The thickness of wood structural panels complying with the specific gravity requirements of Note a shall be permitted to be included in satisfying the minimum required
    penetration into framing.
    d. Where the required cladding fastener penetration into wood material exceeds3/4 inch and is not more than 11/2 inches, a minimum 2-inch nominal wood furring or an
    approved design shall be used.
    e.

  • CRC § 2306.2 High relevance — show source text
    TABLE 2306.2(1)—ALLOWABLE SHEAR VALUES (POUNDS PER FOOT) FOR WOOD STRUCTURAL PANEL DIAPHRAGMS
    UTILIZING STAPLES WITH FRAMING OF DOUGLAS FIR-LARCH, OR SOUTHERN PINEa FOR WIND OR SEISMIC LOADINGf    		 Col2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 Col11
    PANEL
    GRADE    		 STAPLE
    LENGTH
    AND
    GAGEd    		 MINIMUM
    FASTENER
    PENETRATION
    IN FRAMING
    (inches)    		 MINIMUM
    NOMINAL
    PANEL
    THICKNESS
    (inch)    		 MINIMUM
    NOMINAL WIDTH
    OF FRAMING
    MEMBERS AT
    ADJOINING PANEL
    EDGES AND
    BOUNDARIESe
    (inches)    		 BLOCKED DIAPHRAGMS BLOCKED DIAPHRAGMS BLOCKED DIAPHRAGMS BLOCKED DIAPHRAGMS UNBLOCKED DIAPHRAGMS UNBLOCKED DIAPHRAGMS
    PANEL
    GRADE    		 STAPLE
    LENGTH
    AND
    GAGEd    		 MINIMUM
    FASTENER
    PENETRATION
    IN FRAMING
    (inches)    		 MINIMUM
    NOMINAL
    PANEL
    THICKNESS
    (inch)    		 MINIMUM
    NOMINAL WIDTH
    OF FRAMING
    MEMBERS AT
    ADJOINING PANEL
    EDGES AND
    BOUNDARIESe
    (inches)    		 Fastener spacing (inches) at
    diaphragm boundaries
    (all cases) at continuous
    panel edges parallel to load
    (Cases 3, 4), and at all panel
    edges (Cases 5, 6)b    		 Fastener spacing (inches) at
    diaphragm boundaries
    (all cases) at continuous
    panel edges parallel to load
    (Cases 3, 4), and at all panel
    edges (Cases 5, 6)b    		 Fastener spacing (inches) at
    diaphragm boundaries
    (all cases) at continuous
    panel edges parallel to load
    (Cases 3, 4), and at all panel
    edges (Cases 5, 6)b    		 Fastener spacing (inches) at
    diaphragm boundaries
    (all cases) at continuous
    panel edges parallel to load
    **(Cases 3, 4),
  • CRC § 0.90 High relevance — show source text

    00|0.90|DR|DR|DR| |Minimum
    1× wood
    furringd|Minimum
    2× wood
    stud|No.10
    wood
    screw|1|24|4.00|0.90|DR|DR|DR|2.85|DR|DR|DR|DR| |Minimum
    1× wood
    furringd|Minimum
    2× wood
    stud|1/4″
    lag screw|11/2|12|4.00|2.65|1.90|1.50|0.90|4.00|1.65|1.05|0.80|DR| |Minimum
    1× wood
    furringd|Minimum
    2× wood
    stud|1/4″
    lag screw|11/2|16|4.00|1.95|1.25|0.95|0.50|4.00|1.10|0.65|DR|DR| |Minimum
    1× wood
    furringd|Minimum
    2× wood
    stud|1/4″
    lag screw|11/2|24|4.00|1.10|0.65|DR|DR|3.25|0.50|DR|DR|DR| |For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa, 1 pound per square inch = 6.895 kPa.
    DR = Design Required.
    o.c. = On Center.
    a. Wood framing and furring shall be Spruce-pine-fir or any wood species with a specific gravity of 0.42 or greater in accordance with AWC NDS.
    b. Nail fasteners shall comply with ASTM F1667, except nail length shall be permitted to exceed ASTM F1667 standard lengths.
    c. The thickness of wood structural panels complying with the specific gravity requirements of Note a shall be permitted to be included in satisfying the minimum required pene-
    tration into framing.
    d. Where the required cladding fastener penetration into wood material exceeds3/4 inch and is not more than 11/2 inches, a minimum 2× wood furring or an approved design shall
    be used.
    e. Foam sheathing shall have a minimum compressive strength of 15 psi in accordance with ASTM C578 or ASTM C1289.
    f. Furring shall be spaced not more than 24 inches on center, in a vertical or horizontal orientation. In a vertical orientation, furring shall be located over wall studs and attached
    with the required fastener spacing. In a horizontal orientation, the indicated 8-inch and 12-inch fastener spacing in furring shall be achieved by use of two fasteners into studs
    at 16 inches and 24 inches on center, respectively.
    g. Cladding weight is the maximum weight of cladding materials in pounds per square foot of wall area. The 3 psf category typically applies to panel and lap siding materials; the
    11 psf category typically applies to conventional three-coat stucco of7/8-inch thickness; and 15 psf to 25 psf categories typically apply to adhered masonry veneers.|For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa, 1 pound per square inch = 6.895 kPa.
    DR = Design Required.
    o.c. = On Center.
    a.

  • CRC § 12.11.2.2 High relevance — show source text

    Where new members are added as crossties, they shall be spaced no more than 24 feet (7315 mm) apart. Where existing girders are used as crossties, their actual spacing shall be deemed adequate even where the spacing exceeds 24 feet (7315 mm), as long as the girders are provided with continuity connectors as required.

    Wall anchorage shall not be provided by fastening the edge of plywood sheathing to steel ledgers. Wall anchorage shall not be provided solely by fastening the edge of steel decking to steel ledgers unless analysis demonstrates acceptable capacity. The existing connections shall be subject to field verification and the new connections shall be subject to special inspection.

    New wall anchors shall be provided to resist the full wall anchorage design force independent of existing shear or tension anchors.

    Exception: Existing cast-in-place anchors shall be permitted as part of the wall anchorage system if the tie element can be readily attached to the anchors, and if the anchors are capable of resisting the total vertical and lateral shear load (including dead load) while being acted on by the maximum wall anchorage tension force caused by an earthquake. Acceptable tension values for the existing anchors shall be established by testing in accordance with Section A205.4.

    [BS] A206.3 Development of anchor forces into the diaphragm. Development of the required anchorage forces into roof and floor diaphragms shall comply with the requirements of this section and Section 12.11.2.2 of ASCE 7.

    Lengths of development of anchor loads in wood diaphragms shall be based on existing field nailing of the sheathing unless existing edge nailing is positively identified on the original construction plans or at the site.

    [BS] A206.4 Anchorage at pilasters. Where pilasters are present, the wall anchorage system shall comply with the requirements of this section and Section 12.11.2.2.7 of ASCE 7. The pilasters or the walls immediately adjacent to the pilasters shall be anchored directly to the roof framing such that the existing vertical anchor bolts at the top of the pilasters are bypassed without permitting tension or shear failure at the top of the pilasters.

    Exception: If existing vertical anchor bolts at the top of the pilasters are used for the anchorage, additional exterior confinement shall be provided as required to resist the total anchorage force.

    [BS] A206.5 Combination of anchor types. New anchors used in combination on a single framing member shall be of compatible behavior and stiffness.

    [BS] A206.6 Anchorage at interior walls. Existing interior reinforced concrete or reinforced masonry walls that extend to the floor above or to the roof diaphragm shall be anchored for out-of-plane forces per Sections A206.1 and A206.3. Walls extending through

    APPENDIX A-22 2025 CALIFORNIA EXISTING BUILDING CODE

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

    the roof diaphragm shall be anchored for out-of-plane forces on both sides, and continuity ties shall be spliced across or continuous through the interior wall to provide diaphragm continuity.

    [BS] A206.7 Collectors. Collectors designed in accordance with this section shall be provided at reentrant corners and at interior shear walls.

  • CRC § 3.1 High relevance — show source text

    [BS] A406.2 Existing construction. The plans shall show existing diaphragm and shear wall sheathing and framing materials; fastener type and spacing; diaphragm and shear wall connections; continuity ties; collector elements; and the portion of the existing materials that needs verification during construction. If the cap allowed by Section A403.3.1 is used to limit the scope of retrofit, the foregoing information shall be shown for each retrofitted story and at least one story above the uppermost retrofitted story. If the cap allowed by Section A403.3.1 is not used, the foregoing information need only be shown for each retrofitted story and for the floor at the top of that story.

    [BS] A406.3 New construction.

    [BS] A406.3.1 Foundation plan elements. The foundation plan shall include the size, type, location and spacing of all anchor bolts with the required depth of embedment, edge and end distance; the location and size of all shear walls and all columns for braced frames or moment frames; referenced details for the connection of shear walls, braced frames or moment-resisting frames to their footing; and referenced sections for any grade beams and footings.

    [BS] A406.3.2 Framing plan elements. The framing plan shall include the length, location and material of shear walls; the location and material of frames; references or details for the column-to-beam connectors, beam-to-wall connections and shear transfers at floor and roof diaphragms; and the required nailing and length for wall top plate splices.

    APPENDIX A-48 2025 CALIFORNIA EXISTING BUILDING CODE

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

    [BS] A406.3.3 Shear wall schedule, notes and details. Shear walls shall have a referenced schedule on the plans that includes the correct shear wall capacity in pounds per foot (N/m); the required fastener type, length, gage and head size; and a complete specification for the sheathing material and its thickness. The schedule shall also show the required location of 3-inch (76 mm) nominal or two 2-inch (51 mm) nominal edge members; the spacing of shear transfer elements such as framing anchors or added sill plate nails; the required hold-down with its bolt, screw or nail sizes; and the dimensions, lumber grade and species of the attached framing member.

    Notes shall show required edge distance for fasteners of structural wood panels and framing members; required flush nailing at the plywood surface; limits of mechanical penetrations; and the sill plate material assumed in the design. The limits of mechanical penetrations shall be detailed showing the maximum notching and drilled hole sizes.

    [BS] A406.3.4 General notes. General notes shall show the requirements for material testing, special inspection and structural observation.

    SECTION A407—QUALITY CONTROL

    [BS] A407.1 Structural observation. Structural observation, in accordance with Section 1704.6 of the California Building Code is required, regardless of seismic design category, height or other conditions. Structural observation shall include visual observation of work for conformance to the approved construction documents and confirmation of existing conditions assumed during design.

    A407.2 Contractor responsibility. Contractor responsibility shall be in accordance with Section 1704.4 of the California Building Code .

  • 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:

    1. Over a vapor retarder in shower or bathtub compartments.
    2. 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 § 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

    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.) (inch)    		 ** SHEAR VALUEa, b
    (plf of ceiling)**    		 ** MINIMUM FASTENER SIZEc, d**
    Gypsum board or 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 head
    Gypsum board or gypsum
    panel product    		 1/2 24 o.c. 70 5d cooler or wallboard nail;
    15/8-inch long; 0.086-inch shank;
    15/64-inch head
    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. 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 § 0-60 High relevance — show source text

    ****Vasd**
    f (mph)|Mean roof
    height (feet)|All roof slopes|All roof slopes|All roof slopes| |85|0-60|One fastener per tile.|One fastener per tile.|One fastener per tile.| |100|0-40|One fastener per tile.|One fastener per tile.|One fastener per tile.| |100|> 40-60|The head of all tiles shall be nailed. The nose of all eave tiles shall be fastened with approved clips. Rake tiles
    shall be nailed with two nails. The nose of all ridge, hip and rake tiles shall be set in a bead of roofer’s mastic.|The head of all tiles shall be nailed. The nose of all eave tiles shall be fastened with approved clips. Rake tiles
    shall be nailed with two nails. The nose of all ridge, hip and rake tiles shall be set in a bead of roofer’s mastic.|The head of all tiles shall be nailed. The nose of all eave tiles shall be fastened with approved clips. Rake tiles
    shall be nailed with two nails. The nose of all ridge, hip and rake tiles shall be set in a bead of roofer’s mastic.| |110|0-60|The fastening system shall resist the wind forces in Section 1609.6.3.1.|The fastening system shall resist the wind forces in Section 1609.6.3.1.|The fastening system shall resist the wind forces in Section 1609.6.3.1.| |120|0-60|The fastening system shall resist the wind forces in Section 1609.6.3.1.|The fastening system shall resist the wind forces in Section 1609.6.3.1.|The fastening system shall resist the wind forces in Section 1609.6.3.1.| |130|0-60|The fastening system shall resist the wind forces in Section 1609.6.3.1.|The fastening system shall resist the wind forces in Section 1609.6.3.1.|The fastening system shall resist the wind forces in Section 1609.6.3.1.| |All|> 60|The fastening system shall resist the wind forces in Section 1609.6.3.1.|The fastening system shall resist the wind forces in Section 1609.6.3.1.|The fastening system shall resist the wind forces in Section 1609.6.3.1.| |For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s, 1 pound per square foot = 4.882 kg/m2.
    a. Minimum fastener size. Corrosion-resistant nails not less than No. 11 gage with5/16-inch head. Fasteners shall be long enough to penetrate into the sheathing3/4 inch or
    through the thickness of the sheathing, whichever is less. Attaching wire for clay and concrete tile shall not be smaller than 0.083 inch.
    b. Snow areas. Not fewer than two fasteners per tile are required or battens and one fastener.
    c. Roof slopes greater than 24:12. The nose of all tiles shall be securely fastened.
    d. Horizontal battens.

  • CRC § 0.42 High relevance — show source text

    Spacing of fasteners not included in this table shall be based on Table R602.3(2).
    f. For wood structural panel roof sheathing attached to gable end roof framing and to intermediate supports within 48 inches of roof edges and ridges, nails shall be spaced at 4
    inches on center where the ultimate design wind speed is greater than 130 mph in Exposure B or greater than 110 mph in Exposure C. Fastener spacing applies where roof
    framing specific gravity is 0.42 or larger. Where roof framing specific gravity is greater than or equal to 0.35 but less than 0.42 in accordance with AWC NDS, fastening of roof
    sheathing shall be with RSRS-03 (21/2″ × 0.131″ × 0.281″ head) nails.
    g. Gypsum sheathing shall conform to ASTM C1396 and shall be installed in accordance with ASTM C1280 or GA 253 . Fiberboard sheathing shall conform to ASTM C208.
    h. Spacing of fasteners on floor sheathing panel edges applies to panel edges supported by framing members and required blocking and at floor perimeters only. Spacing of fasteners
    on roof sheathing panel edges applies to panel edges supported by framing members and required blocking. Blocking of roof or floor sheathing panel edges perpendicular to the
    framing members need not be provided except as required by other provisions of this code. Floor perimeter shall be supported by framing members or solid blocking.
    i. Where a rafter is fastened to an adjacent parallel ceiling joist in accordance with this schedule, provide two toe nails on one side of the rafter and toe nails from the ceiling joist
    to top plate in accordance with this schedule. The toe nail on the opposite side of the rafter shall not be required.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s; 1 ksi = 6.895 MPa.
    a. Nails are smooth-common, box or deformed shanks except where otherwise stated. Nails used for framing and sheathing connections are carbon steel and shall have mini-
    mum average bending yield strengths as shown: 80 ksi for shank diameter of 0.192 inch (20d common nail), 90 ksi for shank diameters larger than 0.142 inch but not larger than
    0.177 inch, and 100 ksi for shank diameters of 0.142 inch or less. Connections using nails and staples of other materials, such as stainless steel, shall be designed by accepted
    engineering practice or approved under Section R104.2.2.
    b. RSRS-01 is a Roof Sheathing Ring Shank nail meeting the specifications in ASTM F1667.
    c. Nails shall be spaced at not more than 6 inches on center at all supports where spans are 48 inches or greater.
    d. Four-foot by 8-foot or 4-foot by 9-foot panels shall be applied vertically.
    e. Spacing of fasteners not included in this table shall be based on Table R602.3(2).
    f. For wood structural panel roof sheathing attached to gable end roof framing and to intermediate supports within 48 inches of roof edges and ridges, nails shall be spaced at 4
    inches on center where the ultimate design wind speed is greater than 130 mph in Exposure B or greater than 110 mph in Exposure C. Fastener spacing applies where roof
    framing specific gravity is 0.42 or larger.

Frequently asked questions

What is the single required fastener pattern for a gypsum ceiling diaphragm?

Screws spaced 6 in. o.c. at panel edges and 12 in. o.c. in the field, using at least No. 8 or No. 10 screws as required by framing thickness — per § R804.3.7.1.

Can I reduce the diaphragm length required by the table if I add blocking?

Yes — for gypsum board diaphragms the Table R804.3.7.1 length may be multiplied by 0.35 if all panel edges are blocked (or by 0.9 if all edges are screwed at 4 in. o.c.). § R804.3.7.1.

What blocking material is required at the gable end detail?

The code calls for flat blocking of C‑shaped or track section with minimum 33 mils thickness, and gypsum perimeter blocking using 2"×6" wood members where R702.3.6 specifies. § R804.3.7.1 and § R702.3.6.

Do wood structural panel ceilings use the same table as gypsum?

No — wood structural panel sheathed ceilings have fixed minimum lengths: 12 ft (<36 ft building width) or 14 ft (≥36 ft building width) rather than relying on Table R804.3.7.1’s variable values. § R804.3.7.1.

Will I need special inspection for this work?

Possibly. Projects in certain Seismic Design Categories (C, D, E, F) may require periodic special inspection for diaphragm fastening per § 1705.13.2; there are exceptions when sheathing and edge spacing meet specific criteria.

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