CRC · California Residential Code

What are the gypsum board/gypsum-lath backing and installation rules?

For homeowners: The CRC requires gypsum board and panels be installed to ASTM standards, fastened per the CRC’s Table R702.3.5, supported by at least 2‑inch nominal wood framing (or 1‑1/4" steel), applied parallel or perpendicular to studs so edges land on framing, and never left exposed to weather; adhesives must meet ASTM standards and gypsum used as a base for exterior plaster requires a water‑resistive barrier.

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

The California Residential Code requires that materials, supports, adhesives and fasteners for gypsum board and gypsum panel products meet listed ASTM standards and be installed per the CRC rules in § R702.3 and the application/attachment rules in § R702.3.5. Supports (wood or steel), furring and framing minimum sizes are specified, adhesives are limited to specific ASTM types, and the board must be applied either at right angles or parallel to framing with all edges and ends supported by framing members. Also, interior gypsum board shall not be installed where it is directly exposed to the weather or to water.

The single most important rule: Supports and fasteners for gypsum board must comply with Table R702.3.5; gypsum board must be installed so all panel edges and ends occur on framing and must not be left exposed to the weather.

Requirements in detail

Materials & adhesives (what is permitted)

Gypsum board and related panel products must conform to the ASTM standards listed in § R702.3.1.
Expandable-foam adhesives for gypsum panel installation must conform to ASTM D6464; other adhesives must conform to ASTM C557 (see § R702.3.1.1).

Support framing and furring

Wood framing supporting gypsum board must be not less than 2 inches (nominal) in the least dimension. Wood furring strips are permitted at 1 inch by 2 inch (nominal) when installed over solid backing and spaced not more than 24 inches on center. (See § R702.3.2.)
Cold‑formed steel framing must be not less than 1 1/4 inches (32 mm) wide in the least dimension; nonload-bearing and load-bearing steel framing are to comply with AISI S220 and S240 respectively. (See § R702.3.3.)

How panels must be applied (orientation, edge support, exposure)

Panels shall be applied at right angles or parallel to framing members, and all edges and ends shall occur on framing members except those edges/ends perpendicular to framing (see § R702.3.5).
Interior gypsum board shall not be installed where it is directly exposed to the weather or to water. (See § R702.3.5.)

Attachment, supports and fasteners

Supports and fasteners used to attach gypsum board and gypsum panel products shall comply with Table R702.3.5 (or other approved methods). The code text points to that table as the controlling detail for fastening and minimum thickness/application conditions (see § R702.3.1.1 and § R702.3.5).

When gypsum is used as a base for plaster

When gypsum board is used as a base for cement plaster, a water‑resistive barrier complying with § R703.2 is required. (See Table notes and R702.1 commentary referencing gypsum as a base.)

Decision‑relevant dimensions / values (quick reference)

Item / decision	Required value / rule	Code Reference
Minimum wood framing thickness for gypsum supports	2 in. (nominal)	§ R702.3.2
Wood furring allowed over solid backing	1" × 2" (nominal); ≤ 24" o.c.	§ R702.3.2
Minimum cold‑formed steel framing width	1 1/4 in. (32 mm)	§ R702.3.3
Adhesive standards	Expandable foam: ASTM D6464; other adhesives: ASTM C557	§ R702.3.1.1
Panel orientation	At right angles or parallel to framing; edges/ends on framing	§ R702.3.5
Attachment / fasteners	Per Table R702.3.5 (supports and fasteners)	§ R702.3.1.1, § R702.3.5
Interior exposure restriction	Do not install interior gypsum board where directly exposed to the weather or water	§ R702.3.5
Gypsum base for cement plaster	Water‑resistive barrier required per § R703.2	Table note / § R702.1

(Notes: Table R702.3.5 in the CRC contains the comprehensive fastener/attachment and thickness/application matrix; the CRC text requires compliance with that table — see § R702.3.5.)

Exceptions & special cases

The CRC text requires a water‑resistive barrier when gypsum board is used as a base for cement plaster — see § R702.1 note and § R703.2 requirement. If this particular condition applies, do not omit the WRB.
Insulating concrete form (ICF) interior finishes: adhesives are permitted in combination with mechanical fasteners where ICFs are present; adhesives must be compatible with the form materials (see § R702.3.4).
The CRC directs use of Table R702.3.5 for application and attachment details; where the table allows alternative approved methods, the alternative must be specifically approved by the authority having jurisdiction (see § R702.3.1.1 and § R702.3.5).

Note: The California Building Code (CBC) contains more detailed lath/ plaster backing rules (for cement plaster stucco and lath) such as restrictions on using gypsum lath as a direct backing for cement plaster; those CBC provisions are not the CRC proper but are relevant when cement plaster is involved. If you need CBC plaster/lath rules, that is a separate reference.

Common mistakes

Installing panel edges or ends that do not land on framing members — the CRC explicitly requires edges/ends to occur on framing (see § R702.3.5).
Using undersized wood supports or furring — remember the 2 in. nominal minimum for framing and 1"×2" furring only over solid backing and ≤ 24" o.c. (see § R702.3.2).
Leaving interior gypsum exposed to weather or direct water — prohibited by § R702.3.5.
Using adhesives that do not meet the ASTM requirements — expandable‑foam adhesives must meet ASTM D6464 and other adhesives ASTM C557 (see § R702.3.1.1).
Failing to follow Table R702.3.5 for fastening/fastener spacing and panel thickness/application — the code refers to that table as the controlling attachment specification (see § R702.3.5).

Worked example — interior partition (numbers you can apply)

Scenario: You are installing 1/2‑inch gypsum wallboard on an interior partition framed with typical wood studs.

Confirm framing size: use studs with nominal thickness ≥ 2 in. (2x4 studs meet § R702.3.2).
Panel orientation: install the 1/2" gypsum board perpendicular to the studs (right angles) so long edges and ends fall on studs — required by § R702.3.5.
Furring (if used): if you need to fur out a face and you have solid backing, you may use 1" × 2" furring strips spaced not more than 24" on center (see § R702.3.2).
Fasteners/supports: the CRC requires using the supports/fasteners specified in Table R702.3.5 — refer to that table for the correct screw or staple type and spacing for 1/2" board in your application (see § R702.3.1.1 and § R702.3.5). If you do not have the table to hand, obtain it from the CRC to select the correct fastener type/spacing.
Weather exposure: because this is an interior partition, do not worry about WRB for this application — but remember interior gypsum must not be directly exposed to the weather or water (see § R702.3.5).

If you need the exact screw/staple spacing or minimum screw penetration for 1/2" board, the CRC’s Table R702.3.5 provides those specifics and must be consulted; the section text points to the table as the controlling detail.

Related provisions

§ R702.3.1 — Materials standards for gypsum board and panel products.
§ R702.3.1.1 — Adhesive standards (ASTM D6464, ASTM C557) and requirement to comply with Table R702.3.5 for supports/fasteners.
§ R702.3.2 — Wood framing and furring minimum sizes (2" nominal; 1"×2" furring over solid backing ≤24" o.c.).
§ R702.3.3 — Cold‑formed steel framing minimum width (1 1/4").
§ R702.3.4 — Insulating concrete form (ICF) interior finishes — adhesives allowed with fasteners; compatibility requirements.
§ R702.3.5 — Application rules (orientation, edge support, interior exposure prohibition) and the requirement to follow Table R702.3.5.
§ R702.1 (table notes) — When gypsum board is used as a base for cement plaster, a WRB per § R703.2 is required.

Code references

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

CRC § 3.5. High relevance — show source text

Where measured from face of support or backing.
c. Because masonry and concrete surfaces vary in plane, thickness of plaster need not be uniform.
d. Where applied over a liquid bonding agent, finish coat shall be permitted to be applied directly to concrete surface.
e. Approved acoustical plaster shall be permitted to be applied directly to concrete or over base coat plaster, beyond the maximum plaster thickness shown.
f. Attachment shall be in accordance with Table R702.3.5.
g. Where gypsum board is used as a base for cement plaster, a water-resistive barrier complying with Section R703.2 shall be provided.|For SI: 1 inch = 25.4 mm.
a. Where measured from back plane of expanded metal lath, exclusive of ribs, or self-furring lath, plaster thickness shall be3/4 inch minimum.
b. Where measured from face of support or backing.
c. Because masonry and concrete surfaces vary in plane, thickness of plaster need not be uniform.
d. Where applied over a liquid bonding agent, finish coat shall be permitted to be applied directly to concrete surface.
e. Approved acoustical plaster shall be permitted to be applied directly to concrete or over base coat plaster, beyond the maximum plaster thickness shown.
f. Attachment shall be in accordance with Table R702.3.5.
g. Where gypsum board is used as a base for cement plaster, a water-resistive barrier complying with Section R703.2 shall be provided.|

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WALL COVERING

TABLE R702.1(2)—GYPSUM PLASTER PROPORTIONSa	Col2	Col3	Col4	Col5
NUMBER	COAT	PLASTER BASE OR LATH	MAXIMUM VOLUME AGGREGATE PER 100 POUNDS NEAT PLASTERb (cubic feet)	MAXIMUM VOLUME AGGREGATE PER 100 POUNDS NEAT PLASTERb (cubic feet)
NUMBER	COAT	PLASTER BASE OR LATH	Damp Loose Sanda	Perlite or Vermiculitec
Two-coat work	Base coat	Gypsum lath	2.5	2
Two-coat work	Base coat	Masonry	3	3
Three-coat work	First coat	Lath	2d	2
Three-coat work	Second coat	Lath	3d	2e
Three-coat work	First and second coats	Masonry	3	3
For SI: 1 inch = 25.4 mm, 1 cubic foot = 0.0283 m3, 1 pound = 0.454 kg. a. Wood-fibered gypsum plaster shall be mixed in the proportions of 100 pounds of gypsum to not more than 1 cubic foot of sand where applied on masonry or concrete. b. Where determining the amount of aggregate in set plaster, a tolerance of 10 percent shall be allowed. c. Combinations of sand and lightweight aggregate shall be permitted to be used, provided the volume and weight relationship of the combined aggregate to gypsum plaster is maintained. d.

CRC § 2510.4 High relevance — show source text
2510.4 Corrosion resistance. Metal lath and lath attachments shall be of corrosion-resistant material.

2510.5 Backing. Backing or a lath shall provide sufficient rigidity to permit plaster applications.

2025 CALIFORNIA BUILDING CODE 25-7

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GYPSUM PANEL PRODUCTS AND PLASTER

2510.5.1 Support of lath. Where lath on vertical surfaces extends between rafters or other similar projecting members, solid backing shall be installed to provide support for lath and attachments.

2510.5.2 Use of gypsum backing board. Gypsum backing for cement plaster shall be in accordance with Section 2510.5.2.1 or 2510.5.2.2.

2510.5.2.1 Gypsum board as a backing board. Gypsum lath or gypsum wallboard shall not be used as a backing for cement plaster.

Exception: Gypsum lath or gypsum wallboard is permitted, with a water-resistive barrier, as a backing for self-furred metal lath or self-furred wire fabric lath and cement plaster where either of the following conditions occur:
1. On horizontal supports of ceilings or roof soffits.
2. On interior walls.
2510.5.2.2 Gypsum sheathing backing. Gypsum sheathing is permitted as a backing for metal or wire fabric lath and cement plaster on walls. A water-resistive barrier shall be provided in accordance with Section 2510.6.

2510.5.3 Backing not required. Wire backing is not required under expanded metal lath or paperbacked wire fabric lath.

[BF] 2510.6 Water-resistive barriers. Water-resistive barriers shall be installed as required in Section 1403.2 and shall comply with Section 2510.6.1 or 2510.6.2.

Exception: Sections 2510.6.1 and 2510.6.2 shall not apply to construction where accumulation, condensation or freezing of moisture will not damage the materials.

[BF] 2510.6.1 Dry climates. One of the following shall apply for dry (B) climate zones:
1. The water-resistive barrier shall be two layers of 10-minute Grade D paper or have a water resistance equal to or greater than two layers of water-resistive barrier complying with ASTM E2556, Type I. The individual layers shall be installed independently such that each layer provides a separate continuous plane and any flashing, installed in accordance with Section 1404.4 and intended to drain to the water-resistive barrier, is directed between the layers.
2. The water-resistive barrier shall be 60-minute Grade D paper or have a water resistance equal to or greater than one layer of water-resistive barrier complying with ASTM E2556, Type II. The water-resistive barrier shall be separated from the stucco by a layer of foam plastic insulating sheathing or other nonwater absorbing layer, or a drainage space or means of drainage complying with Section 2510.6.2. Flashing installed in accordance with Section 1404.4 and intended to drain to the water-resistive barrier shall be directed to the exterior side of the water-resistive barrier.

CRC § 3.1.1 High relevance — show source text

R702.3.1.1 Adhesives. Expandable foam adhesives for the installation of gypsum board and gypsum panel products shall conform to ASTM D6464. Other adhesives for the installation of gypsum board and gypsum panel products shall conform to ASTM C557. Supports and fasteners used to attach gypsum board and gypsum panel products shall comply with Table R702.3.5 or other approved method.

R702.3.2 Wood framing. Wood framing supporting gypsum board and gypsum panel products shall be not less than 2 inches (51 mm) nominal thickness in the least dimension except that wood furring strips not less than 1-inch by 2-inch (25 mm by 51 mm) nominal dimension shall be permitted to be used over solid backing or framing spaced not more than 24 inches (610 mm) on center.

R702.3.3 Cold-formed steel framing. Cold-formed steel framing supporting gypsum board and gypsum panel products shall be not less than 1 [1] / 4 inches (32 mm) wide in the least dimension. Nonload-bearing cold-formed steel framing shall comply with AISI S220. Load-bearing cold-formed steel framing shall comply with AISI S240.

R702.3.4 Insulating concrete form walls. Foam plastics for insulating concrete form walls constructed in accordance with Sections R404.1.2 and R608 on the interior of habitable spaces shall be protected in accordance with Section R303.4. Use of adhesives in conjunction with mechanical fasteners is permitted. Adhesives used for interior and exterior finishes shall be compatible with the insulating form materials.

R702.3.5 Application. Supports and fasteners used to attach gypsum board and gypsum panel products shall comply with Table R702.3.5. Gypsum sheathing shall be attached to exterior walls in accordance with Table R602.3(1). Gypsum board and gypsum panel products shall be applied at right angles or parallel to framing members. All edges and ends of gypsum board and gypsum panel products shall occur on the framing members, except those edges and ends that are perpendicular to the framing members. Interior gypsum board shall not be installed where it is directly exposed to the weather or to water.

2025 CALIFORNIA RESIDENTIAL CODE 7-5

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WALL COVERING

TABLE R702.3.5—MINIMUM THICKNESS AND APPLICATION OF GYPSUM BOARD AND GYPSUM PANEL PRODUCTS	Col2	Col3	Col4	Col5	Col6	Col7
THICKNESS OF GYPSUM BOARD OR GYPSUM PANEL PRODUCTS (inches)	APPLICATION	ORIENTATION OF GYPSUM BOARD OR GYPSUM PANEL PRODUCTS TO FRAMING	MAXIMUM SPACING OF FRAMING MEMBERS **(inches o.c.

CRC § 3.5. High relevance — show source text

SECTION R702—INTERIOR COVERING

R702.1 General. Interior coverings or wall finishes shall be installed in accordance with this chapter and Tables R702.1(1), R702.1(2), R702.1(3) and R702.3.5. Interior masonry veneer shall comply with the requirements of Section R703.7.1 for support and Section R703.7.4 for anchorage, except an airspace is not required. Interior finishes and materials shall conform to the flame spread and smoke-development requirements of Section R302.9.

**

TABLE R702.1(1)—THICKNESS OF PLASTER	Col2	Col3
PLASTER BASE	FINISHED THICKNESS OF PLASTER FROM FACE OF LATH, MASONRY, CONCRETE (inches)	FINISHED THICKNESS OF PLASTER FROM FACE OF LATH, MASONRY, CONCRETE (inches)
PLASTER BASE	Gypsum Plaster	Cement Plaster
Expanded metal lath	5/8, minimuma	5/8, minimuma
Wire lath	5/8, minimuma	3/4, minimum (interior)b
Wire lath	5/8, minimuma	7/8, minimum (exterior)b
Gypsum lathg	1/2, minimum	3/4, minimum (interior)b
Masonry wallsc	1/2, minimum	1/2, minimum
Monolithic concrete wallsc, d	5/8, maximum	7/8, maximum
Monolithic concrete ceilingsc, d	3/8, maximume	1/2, maximum
Gypsum veneer basef, g	1/16, minimum	3/4, minimum (interior)b
Gypsum sheathingg	—	3/4, minimum (interior)b
Gypsum sheathingg	—	7/8, minimum (exterior)b
For SI: 1 inch = 25.4 mm. a. Where measured from back plane of expanded metal lath, exclusive of ribs, or self-furring lath, plaster thickness shall be3/4 inch minimum. b. Where measured from face of support or backing. c. Because masonry and concrete surfaces vary in plane, thickness of plaster need not be uniform. d. Where applied over a liquid bonding agent, finish coat shall be permitted to be applied directly to concrete surface. e. Approved acoustical plaster shall be permitted to be applied directly to concrete or over base coat plaster, beyond the maximum plaster thickness shown. f. Attachment shall be in accordance with Table R702.3.5. g. Where gypsum board is used as a base for cement plaster, a water-resistive barrier complying with Section R703.2 shall be provided.	For SI: 1 inch = 25.4 mm. a. Where measured from back plane of expanded metal lath, exclusive of ribs, or self-furring lath, plaster thickness shall be3/4 inch minimum. b. Where measured from face of support or backing. c. Because masonry and concrete surfaces vary in plane, thickness of plaster need not be uniform. d. Where applied over a liquid bonding agent, finish coat shall be permitted to be applied directly to concrete surface. e. Approved acoustical plaster shall be permitted to be applied directly to concrete or over base coat plaster, beyond the maximum plaster thickness shown. f.

California Residential Code High relevance — show source text
**
HOURS| |ITEM
CODE|MEMBRANE
THICKNESS|CONSTRUCTION DETAILS|LOAD|TIME|PRE-BMS-92|BMS-92|POST-BMS-92|POST-BMS-92|POST-BMS-92| |F/C-S-34|21/2″|Floor: 2″ reinforced concrete or 2″ precast
reinforced Portland cement concrete or
gypsum slabs, precast slabs to be finished
with1/4″ mortar top coat; ceiling: 2″ precast
reinforced gypsum tile, anchored into
beams with metal ties or clips and covered
with1/2″ 1:3 sanded gypsum plaster.|See
Note 12|4 hrs||1||12–14|4| |F/C-S-35|1″|Floor: 1:3:6 Portland cement, sand and
gravel concrete applied directly to the top of
steel units and 11/2″ thick at top of cells, plus
1/2″ 1:21/2″ cement-sand finish, total thick-
ness at top of cells, 2″; ceiling: 1″ neat
gypsum plaster, back of lath 2″ or more
from underside of cellular steel.|See
Note 15|3 hrs||1||15–18|3| |F/C-S-36|1″|Floor: same as F/C-S-35; ceiling: 1″ gypsum-
vermiculite plaster (ratio of gypsum to
vermiculite 2:1 to 3:1), the back of lath 2″ or
more from under-side of cellular steel.|See
Note 15|4 hrs||1||15–18|4| |F/C-S-37|1″|Floor: same as F/C-S-35; ceiling: 1″ neat
gypsum plaster; back of lath 9″ or more from
underside of cellular steel.|See
Note 15|4 hrs||1||15–18|4| |F/C-S-38|1″|Floor: same as F/C-S-35; ceiling: 1″ gypsum-
vermiculite plaster (ratio of gypsum to
vermiculite 2:1 to 3:1), the back of lath being
9″ or more from underside of cellular steel.|See
Note 15|5 hrs||1||15–18|5| |F/C-S-39|3/4″|Floor: asbestos paper 14 lbs/100 ft2
cemented to steel deck with waterproof
linoleum cement, wood screeds and7/8″
wood floor; ceiling:3/4″ sanded gypsum plas-
ter 1:2 for scratch coat and 1:3 for brown
coat.|See
Note 19|1 hr||1||19–22|1| |F/C-S-40|3/4″|Floor: 11/2″ 1:2:4 Portland cement concrete;
ceiling:3/4″ sanded gypsum plaster 1:2 for
scratch coat and 1:3 for brown coat.
CRC § 17.5 High relevance — show source text
OF**
CEILING (inches)|MINIMUM THICKNESS OF
CEILING (inches)| |FLOOR OR ROOF
CONSTRUCTION|ITEM
NUMBER|CEILING CONSTRUCTION|**4 **
hours|**3 **
hours|**2 **
hours|**1 **
hour|**4 **
hours|**3 **
hours|**2 **
hours|**1 **
hour| |11. 11/2"-deep steel roof
deck on steel-framing wood
fiber insulation board, 17.5
pcf density on top applied
over a 15-lb asphalt-satu-
rated felt. Class A or B roof
covering.|11-1.1|Ceiling of gypsum plaster on metal
lath. Lath attached to3/4" furring
channels with 0.049" (No. 18 B.W.
gage) wire ties spaced 6" on center.
3/4" channels saddle tied to 2" chan-
nels with doubled 0.065" (No. 16
B.W. gage) wire ties. 2" channels
spaced 36" on center suspended 2"
below steel framing and saddle tied
with 0.165" (No. 8 B.W. gage) wire.
Plaster mixed 1:2 for scratch coat
and 1:3 for brown coat, by weight,
gypsum-to-sand aggregate for 1-
hour system. For 2-hour system,
plaster mix is 1:2 by weight, gypsum-
to-sand aggregate.|—|—|11/2|1|—|—|7/8
g|3/4
1| |12. 11/2" deep steel roof deck
on steel-framing insulation
of rigid board consisting of
expanded perlite and fibers
impregnated with integral
asphalt waterproofing;
density 9 to 12 pcf secured to
metal roof deck by1/2"-wide
ribbons of waterproof, cold-
process liquid adhesive
spaced 6" apart. Steel joist or
light steel construction with
metal roof deck, insulation,
and Class A or B built-up roof
covering.e|12-1.1|Gypsum-vermiculite plaster on
metal lath wire tied at 6" intervals to
3/4" furring channels spaced 12" on
center and wire tied to 2" runner
channels spaced 32" on center.
Runners wire tied to bottom chord of
steel joists.|—|—|1|—|—|—|7/8|—| |13. Double wood floor over
wood joists spaced 16" on
center.m, n|13-1.1|Gypsum plaster over3/8" Type X
gypsum lath. Lath initially applied
with not less than four 11/8" by No. 13
gage by19/64" head plasterboard
blued nails per bearing.
CRC § 12-1.1 High relevance — show source text
For 2-hour system,
plaster mix is 1:2 by weight, gypsum-
to-sand aggregate.|—|—|11/2|1|—|—|7/8
g|3/4
1| |12. 11/2" deep steel roof deck
on steel-framing insulation
of rigid board consisting of
expanded perlite and fibers
impregnated with integral
asphalt waterproofing;
density 9 to 12 pcf secured to
metal roof deck by1/2"-wide
ribbons of waterproof, cold-
process liquid adhesive
spaced 6" apart. Steel joist or
light steel construction with
metal roof deck, insulation,
and Class A or B built-up roof
covering.e|12-1.1|Gypsum-vermiculite plaster on
metal lath wire tied at 6" intervals to
3/4" furring channels spaced 12" on
center and wire tied to 2" runner
channels spaced 32" on center.
Runners wire tied to bottom chord of
steel joists.|—|—|1|—|—|—|7/8|—| |13. Double wood floor over
wood joists spaced 16" on
center.m, n|13-1.1|Gypsum plaster over3/8" Type X
gypsum lath. Lath initially applied
with not less than four 11/8" by No. 13
gage by19/64" head plasterboard
blued nails per bearing. Continuous
stripping over lath along all joist lines.
Stripping consists of 3"-wide strips of
metal lath attached by 11/2" by No. 11
gage by1/2" head roofing nails spaced
6" on center. Alternate stripping
consists of 3"-wide 0.049" diameter
wire stripping weighing 1 pound per
square yard and attached by No. 16
gage by 11/2" by3/4" crown width
staples, spaced 4" on center. Where
alternate stripping is used, the lath
nailing shall consist of two nails at
each end and one nail at each inter-
mediate bearing. Plaster mixed 1:2 by
weight, gypsum-to-sand aggregate.|—|—|—|—|—|—|—|7/8| |13. Double wood floor over
wood joists spaced 16" on
center.m, n|13-1.2|Cement or gypsum plaster on metal
lath. Lath fastened with 11/2" by No.
11 gage by7/16" head barbed shank
roofing nails spaced 5" on center.
Plaster mixed 1:2 for scratch coat
and 1:3 for brown coat, by weight,
cement to sand aggregate.|—|—|—|—|—|—|—|5/8| |13. Double wood floor over
wood joists spaced 16" on
center.m, n|13-1.3|Perlite or vermiculite gypsum plaster
on metal lath secured to joists with
11/2" by No.
CRC § 7-4 High relevance — show source text
coat.

Exception: Applications installed in accordance with ASTM C926.

7-4 2025 CALIFORNIA RESIDENTIAL CODE

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WALL COVERING

R702.2.2.2 Curing. The finish coat for two-coat cement plaster shall not be applied sooner than 48 hours after application of the first coat. For three-coat cement plaster, the second coat shall not be applied sooner than 24 hours after application of the first coat. The finish coat for three-coat cement plaster shall not be applied sooner than 48 hours after application of the second coat.

R702.2.3 Support. Support spacing for gypsum or metal lath on walls or ceilings shall not exceed 16 inches (406 mm) for [3] / 8 -inchthick (9.5 mm) or 24 inches (610 mm) for [1] / 2 -inch-thick (12.7 mm) plain gypsum lath. Gypsum lath shall be installed at right angles to support framing with end joints in adjacent courses staggered by not less than one framing space.

R702.3 Gypsum board and gypsum panel products.

R702.3.1 Materials. Gypsum board and gypsum panel product materials and accessories shall conform to ASTM C22, C475, C514, C1002, C1047, C1177, C1178, C1278, C1396, C1658 or C1766 and shall be installed in accordance with the provisions of this section. Adhesives for the installation of gypsum board and gypsum panel products shall conform to ASTM C557.

R702.3.1.1 Adhesives. Expandable foam adhesives for the installation of gypsum board and gypsum panel products shall conform to ASTM D6464. Other adhesives for the installation of gypsum board and gypsum panel products shall conform to ASTM C557. Supports and fasteners used to attach gypsum board and gypsum panel products shall comply with Table R702.3.5 or other approved method.

R702.3.2 Wood framing. Wood framing supporting gypsum board and gypsum panel products shall be not less than 2 inches (51 mm) nominal thickness in the least dimension except that wood furring strips not less than 1-inch by 2-inch (25 mm by 51 mm) nominal dimension shall be permitted to be used over solid backing or framing spaced not more than 24 inches (610 mm) on center.

R702.3.3 Cold-formed steel framing. Cold-formed steel framing supporting gypsum board and gypsum panel products shall be not less than 1 [1] / 4 inches (32 mm) wide in the least dimension. Nonload-bearing cold-formed steel framing shall comply with AISI S220. Load-bearing cold-formed steel framing shall comply with AISI S240.

R702.3.4 Insulating concrete form walls. Foam plastics for insulating concrete form walls constructed in accordance with Sections R404.1.2 and R608 on the interior of habitable spaces shall be protected in accordance with Section R303.4. Use of adhesives in conjunction with mechanical fasteners is permitted. Adhesives used for interior and exterior finishes shall be compatible with the insulating form materials.
CRC § 11-1.1 High relevance — show source text
Noncombus-
tible studs—
interior partition
with plaster each
side|11-1.1|31/4" × 0.044" (No. 18 carbon sheet steel gage) steel studs
spaced 24" on center.5/8" gypsum plaster on metal lath each
side mixed 1:2 by weight, gypsum to sand aggregate.|—|—|—|43/4
d| |11. Noncombus-
tible studs—
interior partition
with plaster each
side|11-1.2|33/8" × 0.055" (No. 16 carbon sheet steel gage) approved nail-
ablek studs spaced 24" on center.5/8" neat gypsum wood-
fibered plaster each side over3/8" rib metal lath nailed to studs
with 6d common nails, 8" on center. Nails driven 11/4" and bent
over.|—|—|55/8|—| |11. Noncombus-
tible studs—
interior partition
with plaster each
side|11-1.3|4" × 0.044" (No. 18 carbon sheet steel gage) channel-shaped
steel studs at 16" on center. On each side approved resilient
clips pressed onto stud flange at 16" vertical spacing,1/4"
pencil rods snapped into or wire tied onto outer loop of clips,
metal lath wire-tied to pencil rods at 6" intervals, 1" perlite
gypsum plaster, each side.|—|75/8
d|—|—| |11. Noncombus-
tible studs—
interior partition
with plaster each
side|11-1.4|21/2" × 0.044" (No. 18 carbon sheet steel gage) steel studs
spaced 16" on center. Wood fibered gypsum plaster mixed 1:1
by weight gypsum to sand aggregate applied on3/4-pound
metal lath wire tied to studs, each side.3/4" plaster applied
over each face, including finish coat.|—|—|41/4
d|—| |12. Wood studs—
interior partition
with plaster each
side|12-1.1l, m|2" × 4" wood studs 16" on center with5/8" gypsum plaster on
metal lath. Lath attached by 4d common nails bent over or No.
14 gage by 11/4" by3/4" crown width staples spaced 6" on
center. Plaster mixed 1:11/2 for scratch coat and 1:3 for brown
coat, by weight, gypsum to sand aggregate.|—|—|—|51/8| |12. Wood studs—
interior partition
with plaster each
side|12-1.2l|2" × 4" wood studs 16" on center with metal lath and7/8" neat
wood-fibered gypsum plaster each side. Lath attached by 6d
common nails, 7" on center. Nails driven 11/4" and bent over.|—|—|51/2
d|—| |12.

CRC § 2511.1 High relevance — show source text

SECTION 2511—INTERIOR PLASTER

2511.1 General. Plastering gypsum plaster or cement plaster shall be not less than three coats where applied over metal lath or wire fabric lath and not less than two coats where applied over other bases permitted by this chapter.

Exception: Gypsum veneer plaster and cement plaster specifically designed and approved for one-coat applications.

2511.1.1 Installation. Installation of lathing and plaster materials shall conform to Table 2511.1.1 and Section 2507.

TABLE 2511.1.1—INSTALLATION OF PLASTER CONSTRUCTION	Col2
MATERIAL	STANDARD
Cement plaster	ASTM C926
Gypsum plaster	ASTM C842
Gypsum veneer plaster	ASTM C843
Interior lathing and furring (gypsum plaster)	ASTM C841
Lathing and furring (cement plaster)	ASTM C1063
Steel framing	ASTM C754; C1007

25-8 2025 CALIFORNIA BUILDING CODE

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

GYPSUM PANEL PRODUCTS AND PLASTER

2511.2 Limitations. Plaster shall not be applied directly to fiber insulation board. Cement plaster shall not be applied directly to gypsum lath or gypsum plaster except as specified in Sections 2510.5.1 and 2510.5.2.

2511.3 Grounds. Where installed, grounds shall ensure the minimum thickness of plaster as set forth in ASTM C842 and ASTM C926. Plaster thickness shall be measured from the face of lath and other bases.

2511.4 Interior masonry or concrete. Condition of surfaces shall be as specified in Section 2510.7. Approved specially prepared gypsum plaster designed for application to concrete surfaces or approved acoustical plaster is permitted. The total thickness of base coat plaster applied to concrete ceilings shall be as set forth in ASTM C842 or ASTM C926. Should ceiling surfaces require more than the maximum thickness permitted in ASTM C842 or ASTM C926, metal lath or wire fabric lath shall be installed on such surfaces before plastering.

2511.5 Wet areas. Showers and public toilet walls shall conform to Sections 1210.2 and 1210.3. Where wood frame walls and partitions are covered on the interior with cement plaster or tile of similar material and are subject to water splash, the framing shall be protected with an approved moisture barrier.

SECTION 2512—EXTERIOR PLASTER

2512.1 General. Plastering with cement plaster shall be not less than three coats where applied over metal lath or wire fabric lath or gypsum board backing as specified in Section 2510.5 and shall be not less than two coats where applied over masonry or concrete. If the plaster surface is to be completely covered by veneer or other facing material, or is completely concealed by another wall, plaster application need only be two coats, provided that the total thickness is as set forth in ASTM C926.

2512.1.1 On-grade floor slab. On wood frame or steel stud construction with an on-grade concrete floor slab system, exterior plaster shall be applied in such a manner as to cover, but not to extend below, the lath and paper. The application of lath, paper and flashing or drip screeds shall comply with ASTM C1063.

CRC § 0.049 High relevance — show source text
18 B.W. gage) steel tie wires. Lath applied over1/2"
spacers made of3/ 4" furring channel with 2" legs bent around
each corner. Spacers located 1" from top and bottom of
member and not greater than 40" on center and wire tied
with a single strand of 0.049" (No. 18 B.W. gage) steel tie
wires. Corner bead tied to the lath at 6" on center along each
corner to provide plaster thickness.|—|—|15/8|—| |1. Steel columns
and all of
primary
trusses—
continued|1-9.1|Minimum W8x35 wide flange steel column (w/d ≥ 0.75) with
each web cavity filled even with the flange tip with normal
weight carbonate or siliceous aggregate concrete (3,000 psi
minimum compressive strength with 145 pcf ± 3 pcf unit
weight). Reinforce the concrete in each web cavity with a
minimum No. 4 deformed reinforcing bar installed vertically
and centered in the cavity, and secured to the column web
with a minimum No. 2 horizontal deformed reinforcing bar
welded to the web every 18" on center vertically. As an alter-
native to the No. 4 rebar,3/4" diameter by 3" long headed
studs, spaced at 12" on center vertically, shall be welded on
each side of the web mid-way between the column flanges.|—|—|—|See
Note n| |2. Webs or
flanges of steel
beams and
girders|2-1.1|Carbonate, lightweight and sand-lightweight aggregate
concrete (not including sandstone, granite and siliceous
gravel) with 3" or finer metal mesh placed 1" from the
finished surface anchored to the top flange and providing not
less than 0.025 square inch of steel area per foot in each
direction.|2|11/2|1|1| |2. Webs or
flanges of steel
beams and
girders|2-1.2|Siliceous aggregate concrete and concrete excluded in Item
2-1.1 with 3" or finer metal mesh placed 1" from the finished
surface anchored to the top flange and providing not less
than 0.025 square inch of steel area per foot in each direction.|21/2|2|11/2|1| |2. Webs or
flanges of steel
beams and
girders|2-2.1|Cement plaster on metal lath attached to3/4" cold-rolled
channels with 0.04" (No. 18 B.W. gage) wire ties spaced 3" to
6" on center. Plaster mixed 1: 21/2 by volume, cement to sand.|—|—|21/2
b|7/8| |2. Webs or
flanges of steel
beams and
girders|2-3.1|Vermiculite gypsum plaster on a metal lath cage, wire tied to
0.165" diameter (No. 8 B.W. gage) steel wire hangers wrapped
around beam and spaced 16" on center.

CRC § 2509.2 High relevance — show source text

2509.2 Base for tile. Materials used as a base for wall tile in tub and shower areas and wall and ceiling panels in shower areas shall be of materials listed in Table 2509.2 and installed in accordance with the manufacturer’s recommendations. Water-resistant gypsum backing board shall be used as a base for tile in water closet compartment walls when installed in accordance with GA-216 or ASTM C840 and the manufacturer’s recommendations. Regular gypsum wallboard is permitted under tile or wall panels in other wall and ceiling areas when installed in accordance with GA 216 or ASTM C840.

TABLE 2509.2—BACKERBOARD MATERIALS	Col2
MATERIAL	STANDARD
Glass mat gypsum backing panel	ASTM C1178
Nonasbestos fiber-cement backer board	ASTM C1288 or ISO 8336, Category C
Fiber-mat reinforced cementitious backer unit	ASTM C1325

2509.3 Limitations. Water-resistant gypsum backing board shall not be used in the following locations:

Over a vapor retarder in shower or bathtub compartments.
Where there will be direct exposure to water or in areas subject to continuous high humidity.

SECTION 2510—LATHING AND FURRING FOR CEMENT PLASTER (STUCCO)

2510.1 General. Exterior and interior cement plaster and lathing shall be done with the appropriate materials listed in Table 2507.2 and Chapter 35.

2510.2 Weather protection. Materials shall be stored in such a manner as to protect them from the weather.

2510.3 Installation. Installation of these materials shall be in compliance with ASTM C926 and ASTM C1063.

2510.4 Corrosion resistance. Metal lath and lath attachments shall be of corrosion-resistant material.

2510.5 Backing. Backing or a lath shall provide sufficient rigidity to permit plaster applications.

2025 CALIFORNIA BUILDING CODE 25-7

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

GYPSUM PANEL PRODUCTS AND PLASTER

2510.5.1 Support of lath. Where lath on vertical surfaces extends between rafters or other similar projecting members, solid backing shall be installed to provide support for lath and attachments.

2510.5.2 Use of gypsum backing board. Gypsum backing for cement plaster shall be in accordance with Section 2510.5.2.1 or 2510.5.2.2.

2510.5.2.1 Gypsum board as a backing board. Gypsum lath or gypsum wallboard shall not be used as a backing for cement plaster.

Exception: Gypsum lath or gypsum wallboard is permitted, with a water-resistive barrier, as a backing for self-furred metal lath or self-furred wire fabric lath and cement plaster where either of the following conditions occur:

On horizontal supports of ceilings or roof soffits.
On interior walls.

2510.5.2.2 Gypsum sheathing backing. Gypsum sheathing is permitted as a backing for metal or wire fabric lath and cement plaster on walls. A water-resistive barrier shall be provided in accordance with Section 2510.6.

2510.5.3 Backing not required. Wire backing is not required under expanded metal lath or paperbacked wire fabric lath.

Frequently asked questions

Can I use any adhesive to install gypsum board?

No. Expandable‑foam adhesives must conform to ASTM D6464 and other adhesives to ASTM C557, per § R702.3.1.1.

Can gypsum board edges float between studs?

No. All edges and ends of gypsum board shall occur on the framing members (except ends perpendicular to framing), per § R702.3.5.

Is regular gypsum board OK as a substrate for exterior cement plaster (stucco)?

The CRC requires a water‑resistive barrier when gypsum board is used as a base for cement plaster (see § R702.1 note referencing § R703.2). For more restrictive rules on backing for cement plaster, consult the CBC (lathing/plaster sections) as well.

What framing sizes do I need under gypsum board?

Wood framing must be at least 2 in. nominal in the least dimension; wood furring may be 1"×2" nominal over solid backing and ≤ 24" o.c. (see § R702.3.2).

Where do I find the required screw/staple spacing and fastener types?

The CRC directs you to Table R702.3.5 for the required supports and fastener details and for minimum thickness/application rules; see § R702.3.1.1 and § R702.3.5.

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What plaster types, coat sequences and minimum/maximum thicknesses are required?

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Interior coverings (R702)

California Residential Code