CRC · California Residential Code

How must gypsum ceilings be fastened to cold‑formed steel joists (screw type/spacing)?

For a homeowner: the CRC requires that drywall ceilings attached to steel joists be fastened with minimum No. 6 bugle‑head screws made for steel (specific ASTM types), the screws must go through the steel with at least three threads showing, and they must be placed no farther apart than 12 inches along each joist (tighter spacing required if the ceiling is also acting as a diaphragm).

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Last reviewed: July 6, 2026

What the code requires — 2–4 sentences

Gypsum ceilings on cold‑formed steel joists must be attached with minimum No. 6 screws of the specified types and styles, and screws must be placed at a maximum spacing of 12 inches on center along the joists. The screws must penetrate the steel sufficiently (extend through the steel with not fewer than three exposed threads) and have corrosion protection. These requirements are called out in § R804.2.5, Table R804.3, and the ceiling‑finish rule § R805.1 of the California Residential Code.

The single most important rule: fasten gypsum ceilings to cold‑formed steel joists with minimum No. 6 bugle‑head screws (ASTM C954 or C1513) at 12" o.c. maximum, and make sure screws extend through the steel at least three exposed threads.

Requirements in detail

Basic required screw type and style

  • Use minimum No. 6 screws to attach gypsum board to cold‑formed steel joists. Bugle‑head style and compliance with ASTM C954 or ASTM C1513 are specified for these attachments. (§ R804.2.5; § R702.3.5.1)

  • Screws for steel‑to‑steel connections (where applicable) must be self‑drilling / self‑tapping and conform to ASTM C1513. (§ R804.2.5)

  • Fasteners must have a rust‑inhibitive coating or be made of non‑corrodible material. (§ R804.2.5)

Minimum penetration / thread engagement

  • For all connections the screw must extend through the steel with not fewer than three exposed threads (i.e., three threads projecting past the steel). (§ R804.2.5)

  • For very thin steel (less than 0.033 inch / 1 mm) the CRC points to Type S screws per ASTM C1002 or bugle head style per ASTM C1513 and a minimum penetration of 3/8 inch (9.5 mm) into the steel when specified. For steel 0.033"–0.112" (1–3 mm) use screws per ASTM C954 or ASTM C1513 bugle head style. (§ R702.3.5.1)

Required spacing and diaphragm rules

  • The mandatory fastening schedule for cold‑formed steel roof/ceiling framing lists gypsum board to ceiling joists — No. 6 screws — 12" o.c. (maximum). See Table R804.3. (Table R804.3 / § R804.3)

  • When gypsum board forms a ceiling diaphragm (special seismic/wind diaphragm requirements) the code prescribes different edge/field spacing for diaphragm performance — screws at maximum 6" o.c. at panel edges and 12" o.c. in the field when used as a diaphragm at gable endwalls (ceiling diaphragm rules). Consult § R804.3.7.1 for diaphragm length and edge/field spacing adjustments.

Joist bracing / interaction with fasteners

  • Ceiling joist top‑flange bracing and continuous straps are fastened to the top flange with one No. 8 screw per joist; blocking and bracing details are in § R804.3.1.3 and associated figures. These bracing screws are separate from the gypsum‑to‑joist No. 6 screws on the underside. (§ R804.3.1.3)

Quick reference table (decision‑relevant values)

Item Required value / note Code reference
Minimum screw size for gypsum to cold‑formed steel joists No. 6 (bugle‑head) § R804.2.5, § R702.3.5.1
Acceptable standards for screws ASTM C954 or ASTM C1513 (bugle head) § R804.2.5, § R702.3.5.1
Maximum spacing along joists 12 inches on center (o.c.) Table R804.3 / § R804.3
Screw thread engagement Not fewer than three exposed threads through the steel § R804.2.5
Thin steel (< 0.033") special note Use Type S (ASTM C1002) or bugle head (ASTM C1513); penetrate ≥ 3/8" § R702.3.5.1
Corrosion protection Fasteners with rust‑inhibitive coating or stainless/other non‑corrodible material § R804.2.5
Ceiling diaphragm fastener spacing (when acting as diaphragm) 6" o.c. at panel edges; 12" o.c. in field (see diaphragm rules) § R804.3.7.1
Top‑flange bracing fastener One No. 8 screw to each joist for lateral bracing § R804.3.1.3

Exceptions & special cases

  • The general attachment rule for gypsum ceilings (No. 6 @ 12" o.c.) is the baseline; if the gypsum ceiling is intended to act as a diaphragm for roof/wind loads at gable endwalls, the code requires different edge/field attachment spacing (6" edge, 12" field) and diaphragm length checks — see § R804.3.7.1.

  • For very thin steel framing (< 0.033") the CRC requires Type S (ASTM C1002) or C1513 bugle‑head screws with a minimum penetration (e.g., 3/8") — read § R702.3.5.1 for thickness‑specific requirements. Do not substitute typical coarse‑thread drywall screws intended solely for wood without confirming the ASTM/type match.

  • Top‑flange bracing and continuous straps called for by § R804.3.1.3 are fastened with No. 8 screws to the top flange — these are bracing fasteners and do not replace the required No. 6 underside fasteners for gypsum attachment.

  • Where the code references “installed in accordance with Section R805,” the ceiling installation must also comply with the interior covering rules listed in § R702.1–R702.6 and § R805.1 (R805 simply points you back to the gypsum/finish rules in chapter R702).

Common mistakes

  • Using screws sized only for wood (wrong head/profile or wrong ASTM) instead of No. 6 bugle‑head screws meeting ASTM C954/C1513. (See § R804.2.5, § R702.3.5.1.)
  • Failing to get three threads of engagement through the steel (insufficient penetration). The code requires at least three exposed threads. (§ R804.2.5)
  • Installing screws farther apart than 12" o.c. along joists for typical gypsum ceiling attachment (or not following diaphragm edge spacing when diaphragm function is required). (Table R804.3; § R804.3.7.1)
  • Forgetting corrosion protection: use screws with appropriate coatings or stainless/approved materials. (§ R804.2.5)

Worked example — concrete scenario with numbers

Scenario: 1/2‑inch gypsum board ceiling installed to cold‑formed steel joists 12 feet long.

  1. Select fasteners: No. 6 bugle‑head screws conforming to ASTM C954 (or ASTM C1513 bugle style) and with a rust‑inhibitive coating. (§ R804.2.5; § R702.3.5.1)

  2. Spacing: apply screws along each joist at 12 inches on center maximum per Table R804.3. (Table R804.3 / § R804.3)

  3. Count per joist: a 12‑ft joist with screws at 12" o.c. will have screws across the length at roughly one per foot — that is 13 screw locations along the 12‑ft run if you place one at each end and then every 12" in between (practical installers often place the first screw ~3/8"–1/2" from the sheet edge and then 12" o.c.). Make sure each screw extends through the steel with ≥ 3 exposed threads. (§ R804.2.5)

  4. If the gypsum ceiling will be used as a diaphragm at a gable endwall, tighten the edge spacing to 6" o.c. at panel edges while keeping 12" o.c. in the field, per § R804.3.7.1.

Note: the worked example shows the spacing rule applied to a single joist. For whole‑room material quantities multiply screws per joist by the number of joists and by the number of boards spanning each joist.

Related provisions

  • § R804.2.5 — Fastening requirements for cold‑formed steel roof framing (screw types, thread engagement, corrosion protection).
  • Table R804.3 / § R804.3 — Roof framing fastening schedule (gypsum board to ceiling joists = No. 6 screws @ 12" o.c.).
  • § R804.3.1.3 — Ceiling joist top flange bracing (bracing fastened with No. 8 screw; blocking details).
  • § R804.3.7.1 — Ceiling diaphragm fastening (edge and field spacing for diaphragms).
  • § R805.1 — Ceiling finishes — ceilings installed according to interior finish rules (§ R702.1–R702.6).
  • § R702.3.5.1 — Screw fastening requirements for gypsum to cold‑formed steel (Type S, ASTM references, penetration depths by steel thickness).

Code references

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

  • CRC § 0.292 High relevance — show source text

    Screws for attaching structural sheathing to cold-formed steel roof framing shall have a minimum head diameter of 0.292 inch (7.4 mm) with countersunk heads and shall be installed with a minimum edge distance of [3] / 8 inch (9.5 mm). Gypsum board ceilings shall be attached to cold-formed steel joists with minimum No. 6 screws conforming to ASTM C954 or ASTM C1513 with a buglehead style and shall be installed in accordance with Section R805. For all connections, screws shall extend through the steel not fewer than three exposed threads. Fasteners shall have rust-inhibitive coating suitable for the installation in which they are being used, or be manufactured from material not susceptible to corrosion.

    R804.2.6 Web holes, web hole reinforcing and web hole patching. Web holes in roof or ceiling joists shall comply with the conditions as prescribed in AISI S230, Section A4.5. Web holes not in conformance to the conditions of AISI S230, Section A4.5 shall be reinforced in accordance with the provisions of AISI S230, Section A4.6 or patched in accordance with the provisions of AISI S230, Section A4.7.

    R804.3 Roof construction. Cold-formed steel roof systems constructed in accordance with the provisions of this section shall consist of both ceiling joists and rafters in accordance with Figure R804.3 and fastened in accordance with Table R804.3.

    2025 CALIFORNIA RESIDENTIAL CODE 8-31

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

    ROOF-CEILING CONSTRUCTION

    FIGURE R804.3—COLD-FORMED STEEL ROOF CONSTRUCTION

    Col1 Col2
    CEILING JOIST
    ½ IN. GYPSUM BOARD
    LOAD-BEARING WALL
    WHEN INSTALLED RAFTER SUPPORT
    BRACE SHALL BE A MINIMUM OF
    350s162-33 MIL C-SECTION, CONNECTED
    TO EACH CEILING JOIST AND RAFTER
    WITH 4 SCREWS AT EACH END (COPE
    FLANGES OF BAR AT CEILING JOIST
    CONNECTION OR USE GUSSET PLATE)    		 6 IN. MAX. TO CENTER
    OF SCREW PATTERN
    EAVE OVERHANG
    2 FT. MAX.
    CEILING JOIST SPAN
    LOAD-BEARING WALL SHALL BE
    INSTALLED WHEN RAFTER BRACE
    IS USED
    LOAD-BEARING WALL

    For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mil = 0.0254 mm.

  • CRC § 2.6 High relevance — show source text

    Gypsum board ceilings shall be attached to cold-formed steel joists with minimum No. 6 screws conforming to ASTM C954 or ASTM C1513 with a bugle-head style and shall be installed in accordance with Section R702. For all connections, screws shall extend through the steel not fewer than three exposed threads. Fasteners shall have a rust-inhibitive coating suitable for the installation in which they are being used, or be manufactured from material not susceptible to corrosion.

    R505.2.6 Web holes, web hole reinforcing and web hole patching. Web holes in floor framing members shall comply with the conditions as prescribed in AISI S230, Section A4.5. Web holes not in compliance with the conditions as prescribed in AISI S230, Section A4.5 shall be reinforced in accordance with the provisions of AISI S230, Section A4.6 or patched in accordance with the provisions of AISI S230, Section A4.7.

    R505.3 Floor construction. Cold-formed steel floors shall be constructed in accordance with this section.

    R505.3.1 Floor-to-foundation or load-bearing wall connections. Cold-formed steel-framed floors shall be anchored to foundations, wood sills or load-bearing walls in accordance with Table R505.3.1(1) and Figure R505.3.1(1), R505.3.1(2), R505.3.1(3), R505.3.1(4), R505.3.1(5) or R505.3.1(6). Anchor bolts shall be located not more than 12 inches (305 mm) from corners or the termination of bottom tracks. Continuous cold-formed steel joists supported by interior load-bearing walls shall be constructed in accordance with Figure R505.3.1(7). Lapped cold-formed steel joists shall be constructed in accordance with Figure R505.3.1(8). End floor joists constructed on foundation walls parallel to the joist span shall be doubled unless a C-shaped bearing stiffener, sized in accordance with Section R505.3.4, is installed web-to-web with the floor joist beneath each supported wall stud, as shown in Figure R505.3.1(9). Fastening of cold-formed steel joists to other framing members shall be in accordance with Section R505.2.5 and Table R505.3.1(2).

    TABLE R505.3.1(1)—FLOOR-TO-FOUNDATION OR BEARING WALL CONNECTION REQUIREMENTSa, b Col2 Col3
    ** FRAMING CONDITION** ** BASIC ULTIMATE WIND SPEED (mph) AND EXPOSURE** ** BASIC ULTIMATE WIND SPEED (mph) AND EXPOSURE**
    ** FRAMING CONDITION** ** 110 mph Exposure Category C or**
    less than 139 mph Exposure Category B    		 ** Less than 139 mph Exposure Category C**
    Floor joist to wall track of exterior wall in accor-
    dance with Figure R505.3.1(1)    		 2-No. 8 screws 3-No. 8 screws
    Rim track or end joist to load-bearing wall top
    track in accordance with Figure R505.3.1(1)    		 1-No. 8 screw at 24 inches o.c. 1-No. 8 screw at 24 inches o.c.
    Rim track or end joist to wood sill in accordance
    with Figure R505.3.1(2)    		 Steel plate spaced at 4 feet o.c. with 4-No.
  • CRC § 1.1 High relevance — show source text

    SECTION R804—COLD-FORMED STEEL ROOF FRAMING

    R804.1 General. Elements shall be straight and free of any defects that would significantly affect their structural performance. Coldformed steel roof framing members shall be in accordance with the requirements of this section.

    R804.1.1 Applicability limits. The provisions of this section shall control the construction of cold-formed steel roof framing for buildings not greater than 60 feet (18 288 mm) perpendicular to the joist, rafter or truss span, not greater than 40 feet (12 192 mm) in width parallel to the joist span or truss, less than or equal to three stories above grade plane and with roof slopes not less than 3:12 (25-percent slope) or greater than 12:12 (100-percent slope). Cold-formed steel roof framing constructed in accordance with the provisions of this section shall be limited to sites where the ultimate design wind speed is less than 140 miles per hour (63 m/s), Exposure Category B or C, and the ground snow load is less than or equal to 70 pounds per square foot (3350 Pa).

    R804.1.1.1 Alternate applications. Cold-formed steel roof and ceiling framing for buildings exceeding the applicability limits of Section R804.1.1 is permitted to be designed and constructed in accordance with AISI S230, subject to the limits therein.

    R804.1.2 In-line framing. Cold-formed steel roof framing constructed in accordance with Section R804 shall be located in line with the tolerances specified in AISI S240, Section B1.2.3.

    R804.2 Structural framing. Load-bearing, cold-formed steel roof framing members shall be in accordance with this section.

    R804.2.1 Material. Load-bearing, cold-formed steel framing members shall be cold formed to shape from structural quality sheet steel complying with the requirements of AISI S240, Section A3.

    R804.2.2 Corrosion protection. Load-bearing, cold-formed steel framing shall have a protective coating complying with AISI S240, Section A4.

    R804.2.3 Dimension, thickness and material grade. Load-bearing, cold-formed steel roof framing members shall comply with AISI S230, Section A4.3 and material grade requirements as specified in AISI S230, Section A4.4.

    R804.2.4 Identification. Load-bearing, cold-formed steel framing members shall meet the product identification requirements of AISI S240, Section A5.5.

    R804.2.5 Fastening requirements. Screws for steel-to-steel connections shall be installed with a minimum edge distance and center-to-center spacing of [1] / 2 inch (12.7 mm), shall be self-drilling tapping and shall conform to ASTM C1513. Structural sheathing shall be attached to cold-formed steel roof rafters with minimum No. 8 self-drilling tapping screws that conform to ASTM C1513. Screws for attaching structural sheathing to cold-formed steel roof framing shall have a minimum head diameter of 0.292 inch (7.4 mm) with countersunk heads and shall be installed with a minimum edge distance of [3] / 8 inch (9.5 mm). Gypsum board ceilings shall be attached to cold-formed steel joists with minimum No. 6 screws conforming to ASTM C954 or ASTM C1513 with a buglehead style and shall be installed in accordance with Section R805. For all connections, screws shall extend through the steel not fewer than three exposed threads.

  • CRC § 2.2 High relevance — show source text

    R804.2.2 Corrosion protection. Load-bearing, cold-formed steel framing shall have a protective coating complying with AISI S240, Section A4.

    R804.2.3 Dimension, thickness and material grade. Load-bearing, cold-formed steel roof framing members shall comply with AISI S230, Section A4.3 and material grade requirements as specified in AISI S230, Section A4.4.

    R804.2.4 Identification. Load-bearing, cold-formed steel framing members shall meet the product identification requirements of AISI S240, Section A5.5.

    R804.2.5 Fastening requirements. Screws for steel-to-steel connections shall be installed with a minimum edge distance and center-to-center spacing of [1] / 2 inch (12.7 mm), shall be self-drilling tapping and shall conform to ASTM C1513. Structural sheathing shall be attached to cold-formed steel roof rafters with minimum No. 8 self-drilling tapping screws that conform to ASTM C1513. Screws for attaching structural sheathing to cold-formed steel roof framing shall have a minimum head diameter of 0.292 inch (7.4 mm) with countersunk heads and shall be installed with a minimum edge distance of [3] / 8 inch (9.5 mm). Gypsum board ceilings shall be attached to cold-formed steel joists with minimum No. 6 screws conforming to ASTM C954 or ASTM C1513 with a buglehead style and shall be installed in accordance with Section R805. For all connections, screws shall extend through the steel not fewer than three exposed threads. Fasteners shall have rust-inhibitive coating suitable for the installation in which they are being used, or be manufactured from material not susceptible to corrosion.

    R804.2.6 Web holes, web hole reinforcing and web hole patching. Web holes in roof or ceiling joists shall comply with the conditions as prescribed in AISI S230, Section A4.5. Web holes not in conformance to the conditions of AISI S230, Section A4.5 shall be reinforced in accordance with the provisions of AISI S230, Section A4.6 or patched in accordance with the provisions of AISI S230, Section A4.7.

    R804.3 Roof construction. Cold-formed steel roof systems constructed in accordance with the provisions of this section shall consist of both ceiling joists and rafters in accordance with Figure R804.3 and fastened in accordance with Table R804.3.

    2025 CALIFORNIA RESIDENTIAL CODE 8-31

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

    ROOF-CEILING CONSTRUCTION

    FIGURE R804.3—COLD-FORMED STEEL ROOF CONSTRUCTION

  • CRC § 0.84 High relevance — show source text

    6 screws in accordance with Section R702. 2. Steel straps with a minimum size of 1 [1] / 2 inches by 33 mils (38 mm by 0.84 mm) shall be installed at a maximum spacing of 4 feet (1219 mm). Straps shall be fastened to the bottom flange at each joist with one No. 8 screw and shall be fastened to blocking with two No. 8 screws. Blocking shall be installed between joists at a maximum spacing of 12 feet (3658 mm) measured along a line of continuous strapping (perpendicular to the joist run), and at the termination of all straps.

    R804.3.1.3 Ceiling joist top flange bracing. The top flanges of ceiling joists shall be laterally braced as required by Tables R804.3.1.1(1) and R804.3.1.1(2), in accordance with one of the following:

    1. Minimum 33-mil (0.84 mm) C-shaped member in accordance with Figure R804.3.1.3(1).
    2. Minimum 33-mil (0.84 mm) track section in accordance with Figure R804.3.1.3(1).
    3. Minimum 33-mil (0.84 mm) hat section in accordance with Figure R804.3.1.3(1).
    4. Minimum 54-mil (1.37 mm) 1 [1] / 2 -inch (38 mm) cold-rolled channel section in accordance with Figure R804.3.1.3(1).
    5. Minimum 1 [1] / 2 -inch by 33-mil (38 mm by 0.84 mm) continuous steel strap in accordance with Figure R804.3.1.3(2).

    Lateral bracing shall be installed perpendicular to the ceiling joists and shall be fastened to the top flange of each joist with one No. 8 screw. Blocking shall be installed between joists in line with bracing at a maximum spacing of 12 feet (3658 mm) measured perpendicular to the joists. Ends of lateral bracing shall be attached to blocking or anchored to a stable building component with two No. 8 screws.

    2025 CALIFORNIA RESIDENTIAL CODE 8-35

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

    ROOF-CEILING CONSTRUCTION

    FIGURE R804.3.1.3(1)—CEILING JOIST TOP FLANGE BRACING WITH C-SHAPED, TRACK OR COLD-ROLLED CHANNEL

    ANCHORAGE AT END IS REQUIRED.

    CEILING FRAMING MEMBERS. GYPSUM BOARD ON BOTTOM CHORD NOT SHOWN FOR CLARITY.

    BRACING. USE 1 NO. 8 SCREW TO EACH JOIST.

    FIGURE R804.3.1.3(2)—CEILING JOIST TOP FLANGE BRACING WITH CONTINUOUS STEEL STRAP AND BLOCKING

    ANCHORAGE AT END IS REQUIRED.

    SHORT SEGMENT OF

    USED AS BLOCKING: AT STRAP SPLICE LOCATIONS, AT ENDS, AND AT MAX. 12 FT O.C.

    For SI: 1 foot = 304.8 mm.

  • CRC § 3.00 High relevance — show source text

    fastener**
    horizontal spacing|24″ o.c. fastener
    horizontal spacing|24″ o.c. fastener
    horizontal spacing|24″ o.c. fastener
    horizontal spacing|24″ o.c. fastener
    horizontal spacing| |CLADDING FASTENER THROUGH
    FOAM SHEATHING INTO:|CLADDING FASTENER TYPE
    AND MINIMUM SIZEb|CLADDING
    FASTENER
    VERTICAL
    SPACING
    (inches)|Cladding weight|Cladding weight|Cladding weight|Cladding weight|Cladding weight|Cladding weight|Cladding weight|Cladding weight| |CLADDING FASTENER THROUGH
    FOAM SHEATHING INTO:|CLADDING FASTENER TYPE
    AND MINIMUM SIZEb|CLADDING
    FASTENER
    VERTICAL
    SPACING
    (inches)|**3 **
    psf|11
    psf|18
    psf|25
    psf|**3 **
    psf|11
    psf|18
    psf|25
    psf| |Cold-formed steel framing
    (minimum penetration of steel
    thickness plus 3 threads)|#8 screw into 33 mil steel or
    thicker|6|3.00|2.95|2.20|1.45|3.00|2.35|1.25|DR| |Cold-formed steel framing
    (minimum penetration of steel
    thickness plus 3 threads)|#8 screw into 33 mil steel or
    thicker|8|3.00|2.55|1.60|0.60|3.00|1.80|DR|DR| |Cold-formed steel framing
    (minimum penetration of steel
    thickness plus 3 threads)|#8 screw into 33 mil steel or
    thicker|12|3.00|1.80|DR|DR|3.00|0.65|DR|DR| |Cold-formed steel framing
    (minimum penetration of steel
    thickness plus 3 threads)|#10 screw into 33 mil steel|6|4.00|3.50|2.70|1.95|4.00|2.90|1.70|0.55| |Cold-formed steel framing
    (minimum penetration of steel
    thickness plus 3 threads)|#10 screw into 33 mil steel|8|4.00|3.10|2.05|1.00|4.00|2.25|0.70|DR| |Cold-formed steel framing
    (minimum penetration of steel
    thickness plus 3 threads)|#10 screw into 33 mil steel|12|4.00|2.25|0.70|DR|3.70|1.05|DR|DR| |Cold-formed steel framing
    (minimum penetration of steel
    thickness plus 3 threads)|#10 screw into 43 mil steel or
    thicker|6|4.00|4.00|4.00|3.60|4.00|4.00|3.45|2.

  • CRC § 5-14 High relevance — show source text

    5-14 2025 CALIFORNIA RESIDENTIAL CODE

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

    FLOORS

    R505.2 Structural framing. Load-bearing cold-formed steel floor framing members shall be in accordance with this section.

    R505.2.1 Material. Load-bearing cold-formed steel framing members shall be cold formed to shape from structural quality sheet steel complying with the requirements of AISI S240, Section A3.

    R505.2.2 Corrosion protection. Load-bearing cold-formed steel framing shall have a metallic coating complying with AISI S240, Section A4.

    R505.2.3 Dimension, thickness and material grade. Load-bearing cold-formed steel floor framing members shall comply with AISI S230, Section A4.3 and material grade requirements as specified in AISI S230, Section A4.4.

    R505.2.4 Identification. Load-bearing cold-formed steel framing members shall meet the product identification requirements of AISI S240, Section A5.5.

    R505.2.5 Fastening. Screws for steel-to-steel connections shall be installed with a minimum edge distance and center-to-center spacing of [1] / 2 inch (12.7 mm), shall be self-drilling tapping, and shall conform to ASTM C1513. Floor sheathing shall be attached to cold-formed steel joists with minimum No. 8 self-drilling tapping screws that conform to ASTM C1513. Screws attaching floor sheathing to cold-formed steel joists shall have a minimum head diameter of 0.292 inch (7.4 mm) with countersunk heads and shall be installed with a minimum edge distance of [3] / 8 inch (9.5 mm). Gypsum board ceilings shall be attached to cold-formed steel joists with minimum No. 6 screws conforming to ASTM C954 or ASTM C1513 with a bugle-head style and shall be installed in accordance with Section R702. For all connections, screws shall extend through the steel not fewer than three exposed threads. Fasteners shall have a rust-inhibitive coating suitable for the installation in which they are being used, or be manufactured from material not susceptible to corrosion.

    R505.2.6 Web holes, web hole reinforcing and web hole patching. Web holes in floor framing members shall comply with the conditions as prescribed in AISI S230, Section A4.5. Web holes not in compliance with the conditions as prescribed in AISI S230, Section A4.5 shall be reinforced in accordance with the provisions of AISI S230, Section A4.6 or patched in accordance with the provisions of AISI S230, Section A4.7.

    R505.3 Floor construction. Cold-formed steel floors shall be constructed in accordance with this section.

    R505.3.1 Floor-to-foundation or load-bearing wall connections. Cold-formed steel-framed floors shall be anchored to foundations, wood sills or load-bearing walls in accordance with Table R505.3.1(1) and Figure R505.3.1(1), R505.3.1(2), R505.3.1(3), R505.3.1(4), R505.3.1(5) or R505.3.1(6). Anchor bolts shall be located not more than 12 inches (305 mm) from corners or the termination of bottom tracks.

  • 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.)
  • CRC § 8-35 High relevance — show source text

    Lateral bracing shall be installed perpendicular to the ceiling joists and shall be fastened to the top flange of each joist with one No. 8 screw. Blocking shall be installed between joists in line with bracing at a maximum spacing of 12 feet (3658 mm) measured perpendicular to the joists. Ends of lateral bracing shall be attached to blocking or anchored to a stable building component with two No. 8 screws.

    2025 CALIFORNIA RESIDENTIAL CODE 8-35

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

    ROOF-CEILING CONSTRUCTION

    FIGURE R804.3.1.3(1)—CEILING JOIST TOP FLANGE BRACING WITH C-SHAPED, TRACK OR COLD-ROLLED CHANNEL

    ANCHORAGE AT END IS REQUIRED.

    CEILING FRAMING MEMBERS. GYPSUM BOARD ON BOTTOM CHORD NOT SHOWN FOR CLARITY.

    BRACING. USE 1 NO. 8 SCREW TO EACH JOIST.

    FIGURE R804.3.1.3(2)—CEILING JOIST TOP FLANGE BRACING WITH CONTINUOUS STEEL STRAP AND BLOCKING

    ANCHORAGE AT END IS REQUIRED.

    SHORT SEGMENT OF

    USED AS BLOCKING: AT STRAP SPLICE LOCATIONS, AT ENDS, AND AT MAX. 12 FT O.C.

    For SI: 1 foot = 304.8 mm.

    R804.3.1.4 Ceiling joist splicing. Splices in ceiling joists shall be permitted, if ceiling joist splices are supported at interior bearing points and are constructed in accordance with Figure R804.3.1.4. The number of screws on each side of the splice shall be the same as required for the heel joint connection in Table R804.3.1.1(3).

    8-36 2025 CALIFORNIA RESIDENTIAL CODE

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

    ROOF-CEILING CONSTRUCTION

    FIGURE R804.3.1.4—SPLICED CEILING JOISTS

    TRACK

    For SI: 1 inch = 25.4 mm.

    R804.3.2 Roof rafters. Cold-formed steel roof rafters shall be in accordance with this section.

    R804.3.2.1 Minimum roof rafter sizes. Roof rafter size and thickness shall be determined in accordance with the limits set forth in Table R804.3.2.1(1) based on the horizontal projection of the roof rafter span. For determination of roof rafter sizes, reduction of roof spans shall be permitted where a roof rafter support brace is installed in accordance with Section R804.3.2.2. The reduced roof rafter span shall be taken as the larger of the distances from the roof rafter support brace to the ridge or to the heel measured horizontally.

    For the purpose of determining roof rafter sizes in Table R804.3.2.1(1), ultimate design wind speeds shall be converted to equivalent ground snow loads in accordance with Table R804.3.2.1(2). Roof rafter sizes shall be based on the higher of the ground snow load or the equivalent snow load converted from the ultimate design wind speed.

    |TABLE R804.3.2.1(1)—ROOF RAFTER SPANSa, b, c,

  • CRC § 3.2 High relevance — show source text

    Deflection criteria:L/480 for live loads,L/240 for total loads.
    b. Floor dead load = 10 psf.
    c. Table provides the maximum clear span in feet and inches.
    d. Bearing stiffeners are to be installed at all support points and concentrated loads.
    e. Minimum Grade 33 ksi steel shall be used for 33 mil and 43 mil thickness. Minimum Grade 50 ksi steel shall be used for 54 and 68 mil thickness.
    f. Table R505.3.2 is not applicable for 800S162-33 and 1000S162-43 continuous joist members.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa, 1 mil = 0.0254 mm.
    a. Deflection criteria:L/480 for live loads,L/240 for total loads.
    b. Floor dead load = 10 psf.
    c. Table provides the maximum clear span in feet and inches.
    d. Bearing stiffeners are to be installed at all support points and concentrated loads.
    e. Minimum Grade 33 ksi steel shall be used for 33 mil and 43 mil thickness. Minimum Grade 50 ksi steel shall be used for 54 and 68 mil thickness.
    f. Table R505.3.2 is not applicable for 800S162-33 and 1000S162-43 continuous joist members.|

    5-20 2025 CALIFORNIA RESIDENTIAL CODE

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

    FLOORS

    R505.3.3 Joist bracing and blocking. Joist bracing and blocking shall be in accordance with this section.

    R505.3.3.1 Joist top flange bracing. The top flanges of cold-formed steel joists shall be laterally braced by the application of floor sheathing fastened to the joists in accordance with Section R505.2.5 and Table R505.3.1(2).

    R505.3.3.2 Joist bottom flange bracing/blocking. Floor joists with spans that exceed 12 feet (3658 mm) shall have the bottom flanges laterally braced in accordance with one of the following:

    1. Gypsum board installed with minimum No. 6 screws in accordance with Section R702.
    2. Continuous steel straps installed in accordance with Figure R505.3.3.2(1). Steel straps shall be spaced at not greater than 12 feet (3658 mm) on center and shall be not less than 1 [1] / 2 inches (38 mm) in width and 33 mils (0.84 mm) in thickness. Straps shall be fastened to the bottom flange of each joist with one No. 8 screw, fastened to blocking with two No. 8 screws, and fastened at each end (of strap) with two No. 8 screws. Blocking in accordance with Figure R505.3.3.2(1) or R505.3.3.2(2) shall be installed between joists at each end of the continuous strapping and at a maximum spacing of 12 feet (3658 mm) measured along the continuous strapping (perpendicular to the joist run). Blocking shall also be located at the termination of all straps.
  • CRC § 3.3 High relevance — show source text

    R505.3.3 Joist bracing and blocking. Joist bracing and blocking shall be in accordance with this section.

    R505.3.3.1 Joist top flange bracing. The top flanges of cold-formed steel joists shall be laterally braced by the application of floor sheathing fastened to the joists in accordance with Section R505.2.5 and Table R505.3.1(2).

    R505.3.3.2 Joist bottom flange bracing/blocking. Floor joists with spans that exceed 12 feet (3658 mm) shall have the bottom flanges laterally braced in accordance with one of the following:

    1. Gypsum board installed with minimum No. 6 screws in accordance with Section R702.
    2. Continuous steel straps installed in accordance with Figure R505.3.3.2(1). Steel straps shall be spaced at not greater than 12 feet (3658 mm) on center and shall be not less than 1 [1] / 2 inches (38 mm) in width and 33 mils (0.84 mm) in thickness. Straps shall be fastened to the bottom flange of each joist with one No. 8 screw, fastened to blocking with two No. 8 screws, and fastened at each end (of strap) with two No. 8 screws. Blocking in accordance with Figure R505.3.3.2(1) or R505.3.3.2(2) shall be installed between joists at each end of the continuous strapping and at a maximum spacing of 12 feet (3658 mm) measured along the continuous strapping (perpendicular to the joist run). Blocking shall also be located at the termination of all straps. As an alternative to blocking at the ends, anchoring the strap to a stable building component with two No. 8 screws shall be permitted.

    FIGURE R505.3.3.2(1)—JOIST BLOCKING (SOLID)

    JOIST

    CONTINUOUS 1 / IN. X 33 1 2 NO. 8 SCREW THROUGHSTRAP TO JOIST (TYP.) MIL STEEL STRAP

    For SI: 1 mil = 0.0254 mm, 1 inch = 25.4 mm.

    FIGURE R505.3.3.2(2)—JOIST BLOCKING (STRAP)

    For SI: 1 mil = 0.0254 mm, 1 inch = 25.4 mm.

    2025 CALIFORNIA RESIDENTIAL CODE 5-21

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

    FLOORS

    R505.3.3.3 Blocking at interior bearing supports. Blocking is not required for continuous back-to-back floor joists at bearing supports. Blocking shall be installed between every other joist for single continuous floor joists across bearing supports in accordance with Figure R505.3.1(7). Blocking shall consist of C-shaped or track section with a minimum thickness of 33 mils (0.84 mm). Blocking shall be fastened to each adjacent joist through a 33-mil (0.84 mm) clip angle, bent web of blocking or flanges of web stiffeners with two No. 8 screws on each side. The minimum depth of the blocking shall be equal to the depth of the joist minus 2 inches (51 mm). The minimum length of the angle shall be equal to the depth of the joist minus 2 inches (51 mm).

  • CRC § 8-31 High relevance — show source text

    R804.3 Roof construction. Cold-formed steel roof systems constructed in accordance with the provisions of this section shall consist of both ceiling joists and rafters in accordance with Figure R804.3 and fastened in accordance with Table R804.3.

    2025 CALIFORNIA RESIDENTIAL CODE 8-31

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

    ROOF-CEILING CONSTRUCTION

    FIGURE R804.3—COLD-FORMED STEEL ROOF CONSTRUCTION

    Col1 Col2
    CEILING JOIST
    ½ IN. GYPSUM BOARD
    LOAD-BEARING WALL
    WHEN INSTALLED RAFTER SUPPORT
    BRACE SHALL BE A MINIMUM OF
    350s162-33 MIL C-SECTION, CONNECTED
    TO EACH CEILING JOIST AND RAFTER
    WITH 4 SCREWS AT EACH END (COPE
    FLANGES OF BAR AT CEILING JOIST
    CONNECTION OR USE GUSSET PLATE)    		 6 IN. MAX. TO CENTER
    OF SCREW PATTERN
    EAVE OVERHANG
    2 FT. MAX.
    CEILING JOIST SPAN
    LOAD-BEARING WALL SHALL BE
    INSTALLED WHEN RAFTER BRACE
    IS USED
    LOAD-BEARING WALL

    For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mil = 0.0254 mm.

    TABLE R804.3—ROOF FRAMING FASTENING SCHEDULEa, b Col2 Col3 Col4 Col5 Col6 Col7 Col8
    ** DESCRIPTION OF BUILDING ELEMENTS** ** DESCRIPTION OF BUILDING ELEMENTS** ** DESCRIPTION OF BUILDING ELEMENTS** ** NUMBER AND SIZE OF FASTENERSa** ** NUMBER AND SIZE OF FASTENERSa** ** NUMBER AND SIZE OF FASTENERSa** ** NUMBER AND SIZE OF FASTENERSa** ** SPACING OF FASTENERS**
    Roof sheathing
    (oriented strand board or plywood) to rafter    		 Roof sheathing
    (oriented strand board or plywood) to rafter    		 Roof sheathing
    (oriented strand board or plywood) to rafter    		 No. 8 screws No. 8 screws No. 8 screws No. 8 screws 6″ o.c. on edges and 12″
    o.c. at interior supports.
    6″ o.c. at gable end truss.
    Gypsum board to ceiling joists Gypsum board to ceiling joists Gypsum board to ceiling joists No. 6 screws No. 6 screws No. 6 screws No. 6 screws 12″ o.c.
    Gable end truss to endwall top track Gable end truss to endwall top track Gable end truss to endwall top track No. 10 screws No. 10 screws No. 10 screws No. 10 screws 12″ o.c.
    Rafter to ceiling joist and to ridge member Rafter to ceiling joist and to ridge member Rafter to ceiling joist and to ridge member Minimum No. 10 screws, in accordance with Table R804.3.1.1(3) Minimum No. 10 screws, in accordance with Table R804.3.1.1(3) Minimum No.
  • CRC § 12.7 High relevance — show source text

    ** Screws for steel-to-steel connections shall be installed with a minimum edge distance and center-to-center spacing of [1] / 2 inch (12.7 mm), shall be self-drilling tapping and shall conform to ASTM C1513. Structural sheathing shall be attached to cold-formed steel studs with minimum No. 8 self-drilling tapping screws that conform to ASTM C1513. Screws for attaching structural sheathing to cold-formed steel wall framing shall have a minimum head diameter of 0.292 inch (7.4 mm) with countersunk heads and shall be installed with a minimum edge distance of [3] / 8 inch (9.5 mm). Gypsum board shall be attached to cold-formed steel wall framing with minimum No. 6 screws conforming to ASTM C954 or ASTM C1513 with a bugle-head style and shall be installed in accordance with Section R702. For connections, screws shall extend through the steel not fewer than three exposed threads. Fasteners shall have rust-inhibitive coating suitable for the installation in which they are being used, or be manufactured from material not susceptible to corrosion.

    R603.2.6 Web holes, web hole reinforcing and web hole patching. Web holes in wall studs shall comply with the conditions as prescribed in AISI S230, Section A4.5. Web holes not in conformance to the conditions as prescribed in AISI S230, Section A4.5 shall be reinforced in accordance with the provisions of AISI S230, Section A4.6 or patched in accordance with the provisions of AISI S230, Section A4.7.

    R603.3 Wall construction. Exterior cold-formed steel framed walls and interior load-bearing cold-formed steel framed walls shall be constructed in accordance with the provisions of this section.

    R603.3.1 Wall to foundation or floor connection. Cold-formed steel framed walls shall be anchored to foundations or floors in accordance with Table R603.3.1 and Figure R603.3.1(1), R603.3.1(2), R603.3.1(3) or R603.3.1(4). Anchor bolts shall be located not more than 12 inches (305 mm) from corners or the termination of bottom tracks. Anchor bolts shall extend not less than 15 inches (381 mm) into masonry or 7 inches (178 mm) into concrete. Foundation anchor straps shall be permitted, in lieu of anchor bolts, if spaced as required to provide equivalent anchorage to the required anchor bolts and installed in accordance with manufacturer’s requirements.

  • CRC § 304.8 High relevance — show source text

    Screws shall be No. 10 minimum.|For SI: 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa.
    a. Screws shall be No. 10 minimum.|For SI: 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa.
    a. Screws shall be No. 10 minimum.|For SI: 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa.
    a. Screws shall be No. 10 minimum.|For SI: 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa.
    a. Screws shall be No. 10 minimum.|

    2025 CALIFORNIA RESIDENTIAL CODE 8-39

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

    ROOF-CEILING CONSTRUCTION

    R804.3.2.5 Roof rafter bottom flange bracing. The bottom flanges of roof rafters shall be continuously braced, at a maximum spacing of 4 feet (1219 mm) as measured parallel to the roof rafters, with one of the following members:

    1. Minimum 33-mil (0.84 mm) C-shaped member.
    2. Minimum 33-mil (0.84 mm) track section.
    3. Minimum 1 [1] / 2 -inch by 33-mil (38 mm by 0.84 mm) steel strap.

    The bracing element shall be fastened to the bottom flange of each roof rafter with one No. 8 screw and shall be fastened to blocking with two No. 8 screws. Blocking shall be installed between roof rafters in-line with the continuous bracing at a maximum spacing of 12 feet (3658 mm) measured perpendicular to the roof rafters. The ends of continuous bracing shall be fastened to blocking or anchored to a stable building component with two No. 8 screws.

    R804.3.3 Cutting and notching. Flanges and lips of load-bearing, cold-formed steel roof framing members shall not be cut or notched.

    R804.3.4 Headers. Roof-ceiling framing above wall openings shall be supported on headers. The allowable spans for headers in load-bearing walls shall not exceed the values set forth in Section R603.6 and Tables R603.6(1) through R603.6(6).

    R804.3.5 Framing of openings in roofs and ceilings. Openings in roofs and ceilings shall be framed with header and trimmer joists. Header joist spans shall not exceed 4 feet (1219 mm) in length. Header and trimmer joists shall be fabricated from joist and track members having a minimum size and thickness equivalent to the adjacent ceiling joists or roof rafters and shall be installed in accordance with Figures R804.3.5(1) and R804.3.5(2). Each header joist shall be connected to trimmer joists with not less than four 2-inch by 2-inch (51 by 51 mm) clip angles. Each clip angle shall be fastened to both the header and trimmer joists with four No. 8 screws, evenly spaced, through each leg of the clip angle. The steel thickness of the clip angles shall be not less than that of the ceiling joist or roof rafter.

  • 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.

Frequently asked questions

Can I use standard drywall screws that I buy for wood framing on steel joists?

No. Use the screw types the code calls out for steel framing (minimum No. 6 bugle‑head meeting ASTM C954 or ASTM C1513, or Type S per ASTM C1002 for very thin steel). The CRC requires specific ASTM conformance for steel framing. (§ R804.2.5; § R702.3.5.1)

What if my steel joists are very thin (less than 0.033")?

For steel thinner than 0.033 inch (1 mm) the code directs use of Type S (ASTM C1002) or bugle head style (ASTM C1513) and specifies minimum penetration (see § R702.3.5.1). Check the joist thickness and select the appropriate screw and penetration.

Do screws have to penetrate through the steel?

Yes — for all connections the CRC requires screws to extend through the steel with not fewer than three exposed threads. (§ R804.2.5)

Is the 12" spacing ever changed?

Yes — when gypsum is used as a ceiling diaphragm, the code prescribes 6" o.c. at panel edges and 12" o.c. in the field for diaphragm performance; otherwise the general gypsum‑to‑joist fastening is 12" o.c. per Table R804.3. (Table R804.3; § R804.3.7.1)

Do I need to coat screws or use stainless?

Fasteners must have a rust‑inhibitive coating suitable for the installation or be manufactured of non‑corrodible material. Choose coatings/materials appropriate for the environment. (§ R804.2.5)

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California Residential Code