CRC · California Residential Code

What water-resistive barrier is required beneath exterior wall coverings?

Q: Must every exterior wall have a WRB?

Yes — one continuous layer of WRB is required over studs or sheathing on all exterior walls unless the accessory structure exception applies (see § R703.2 ).

Q: What about WRB at deck ledgers?

WRB must lap over the vertical leg of ledger flashing ≥ 2 in (51 mm) (or to the vertical leg height, whichever is less) and continue behind the ledger and flashing per § R507.9.1.6 .

Homeowner summary: The California Residential Code requires a continuous water‑resistive barrier (like No.15 felt or an approved membrane) behind all exterior siding or stucco so water is kept out of the wall — it must be lapped, flashed, and in some climates include a drainage space to keep moisture out of your walls (see § R703.2 and the stucco rules in § R703.7.3).

Ask a question free See coverage

Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

The California Residential Code requires at least one continuous layer of a water‑resistive barrier (WRB) installed over studs or sheathing behind all exterior wall veneer, with flashing per § R703.4. This WRB must comply with one of the listed material options (e.g., No. 15 felt, ASTM E2556 Type 1 or 2, foam plastic insulating‑sheathing systems, or ASTM E331 tested assemblies) and be terminated/ lapped so it remains continuous to the top of walls and at penetrations, per § R703.2 . Where the WRB also serves as part of a continuous air barrier, it must be installed in accordance with § N1102.5.1.1 as required by § R703.2 .

The single most important rule: install a continuous, code‑listed water‑resistive barrier behind exterior cladding and integrate it with flashing so water drains to the exterior (see § R703.2).

Requirements in detail

Materials permitted (baseline)

The WRB material options spelled out in § R703.2 are (select one):

No. 15 asphalt felt (ASTM D226, Type 1).
Materials complying with ASTM E2556 (Type 1 or Type 2).
Foam plastic insulating sheathing WRB systems installed per manufacturer and complying with § R703.1.1.
WRB demonstrated by testing to ASTM E331 in accordance with § R703.1.1.
Other approved materials installed according to manufacturer instructions when approved by the authority having jurisdiction.

Application and continuity

At least one layer is required on studs or sheathing for all exterior walls unless specifically exempted; WRB must be continuous to the top of walls and properly terminated at penetrations and appendages, per § R703.2 .
If the WRB doubles as an air barrier, install to meet § N1102.5.1.1 requirements (air‑barrier detailing) as stated in § R703.2 .

Overlap and lap details (No. 15 felt and ASTM E2556 barriers)

Horizontal application required for No. 15 felt and ASTM E2556 WRBs.
Upper layer lap over lower layer: not less than 2 inches (51 mm).
Joints (end laps): not less than 6 inches (152 mm).
All of the above from § R703.2 .

Stucco (plaster) and climate‑sensitive requirements

Stucco (cement plaster) has additional WRB rules depending on California climate zones (see § R703.7.3):

In Dry (B) climates: WRB must be either
- Two layers of 10‑minute Grade D paper (each layer independent), or
- One layer of 60‑minute Grade D paper (or equivalent) provided the WRB is separated from the stucco by foam sheathing, other non‑water‑absorbing layer, or a drainage space/means of drainage.
In Moist (A) or Marine (C) climates: in addition to the Dry‑climate rules, add either a drainage space not less than 3/16 inch (5 mm) on the exterior side of the WRB or achieve ≥ 90% drainage efficiency per ASTM E2273/Annex A2 of ASTM E2925. See § R703.7.3.1 and § R703.7.3.2 .

Accessory structures exception

A WRB is not required for unconditioned detached tool sheds, storage sheds, playhouses and similar accessory structures provided all of these apply:

Siding is attached directly to studs;
Exterior walls are uninsulated; and
Interior side of exterior walls has no wall covering or finishes. (Exception in § R703.2) .

Decision‑relevant dimensions / values

Requirement / value	What to do	Code reference
Minimum WRB layers	1 layer on all exterior walls (unless exception)	§ R703.2
Accepted materials	No. 15 felt (ASTM D226 Type 1), ASTM E2556 Type 1/2, foam sheathing systems, ASTM E331 tested assemblies, or approved alternatives	§ R703.2
Felt/ASTM E2556 horizontal laps	Upper over lower ≥ 2 in (51 mm); joints ≥ 6 in (152 mm)	§ R703.2
Stucco — Dry climates	Two layers 10‑min Grade D paper OR one 60‑min Grade D paper with separation/drainage	§ R703.7.3.1
Stucco — Moist/Marine climates	Above + drainage space ≥ 3/16 in (5 mm) OR ≥ 90% drainage efficiency	§ R703.7.3.2
WRB + ledger flashing	WRB must lap over vertical leg of ledger flashing ≥ 2 in (51 mm) or height of vertical leg, whichever is less	§ R507.9.1.6

Exceptions & special cases

Accessory structures (unconditioned tool sheds, playhouses, storage sheds) may omit WRB if they meet the three‑part exception criteria in § R703.2 .
Where an exterior wall has been tested to resist wind‑driven rain per ASTM E331 (test assembly criteria in § R703.1.1), some WRB/drainage requirements may be relaxed—see § R703.1.1 for test conditions and limits. Note: the CRC requires specific ASTM E331 testing size, differential pressure and exposure duration for this exception to apply. .
For EIFS with drainage, a WRB requirement is referenced to EIFS standards and Section R703.9 (EIFS specific rules) and may require WRB compliance with ASTM E2570 or § 1403.2 in the CBC for non‑residential applications—follow the EIFS section and manufacturer instructions. .

If you need the exact flashing details that must integrate with the WRB, see § R703.4 (flashing) — that section is cross‑referenced repeatedly in § R703.2 and related provisions; consult the code text for the full flashing requirements (the WRB must be lapped and flashed so water drains to the exterior) .

Common mistakes

Installing WRB only on the interior side of sheathing or discontinuing it at penetrations — WRB must be continuous to the top of walls and properly terminated at penetrations per § R703.2 .
Forgetting required laps: No. 15 felt / ASTM E2556 WRBs must be applied horizontally with 2 in head laps and 6 in end laps — skipping these reduces water shedding performance (see § R703.2) .
Using stucco‑appropriate WRB details from Dry climate in Moist/Marine zones (or vice versa). Stucco has climate‑dependent rules (two‑layer vs. drainage space/efficiency) in § R703.7.3 and § R703.7.3.2 .
Lapping WRB incorrectly at deck ledgers/ledger flashing — the WRB must lap over the vertical leg ≥ 2 in (51 mm) or the vertical leg height, per § R507.9.1.6 .
Assuming any peel‑and‑stick membrane is acceptable without checking ASTM/approval or manufacturer instructions — materials must comply with the code options in § R703.2 or be “other approved materials” installed per manufacturer instructions and approved by the authority having jurisdiction .

Worked example — concrete scenario with numbers

Scenario: A new wood‑framed, single‑family home in a Marine (C) climate zone will have a three‑coat stucco exterior over wood sheathing. There is also a deck ledger attached to the exterior wall.

Apply the code as follows:

Select WRB strategy per stucco + Marine climate: choose either
- Two layers of 10‑minute Grade D paper (installed independently so each layer is a continuous plane) — and direct flashing drainage between the layers; OR
- One layer of 60‑minute Grade D paper (or equivalent) plus a separation such as foam plastic insulating sheathing or a drainage space of at least 3/16 inch (5 mm) on the exterior side of the WRB; alternatively demonstrate ≥ 90% drainage efficiency for the drainage mat, per § R703.7.3.1 and § R703.7.3.2 .
For felt option if used: install felt horizontally, lap upper layer over lower by ≥ 2 in (51 mm); lap joints ≥ 6 in (152 mm) as required by § R703.2 .
Where the deck ledger flashing intersects the WRB, lap the WRB over the vertical leg of the ledger flashing by ≥ 2 in (51 mm) (or the vertical leg height if less) and continue the WRB behind the ledger per § R507.9.1.6 .
Terminate WRB continuously to the top of the walls and at all window/door penetrations per § R703.2; integrate flashing per § R703.4 so water is directed to the exterior .

This satisfies the minimum WRB layer requirement and the additional drainage needs for stucco in a marine climate.

Related provisions

§ R703.1 — General exterior wall envelope / water‑resistance and ASTM E331 testing conditions.
§ R703.4 — Flashing requirements (WRB must be integrated with flashing).
§ R703.7.3 — Stucco (cement plaster) WRB and climate‑dependent drainage rules.
§ R703.9 — Exterior insulation and finish systems (EIFS) and drainage WRB specifics.
§ R703.12 — Adhered masonry veneer WRB requirements and laps over screeds.
§ R507.9.1.6 — WRB lapping at deck ledgers and ledger flashing.
§ N1102.5.1.1 — Air‑barrier installation when WRB doubles as air barrier (referenced from § R703.2).

Code references

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

CRC § 2.4. High relevance — show source text
2.4. Exterior wall envelope assemblies shall be subjected to the minimum test exposure for a minimum of 2 hours. The exterior wall envelope design shall be considered to resist wind-driven rain where the results of testing indicate that water did not penetrate control joints in the exterior wall envelope, joints at the perimeter of openings penetration or intersections of terminations with dissimilar materials.

R703.1.2 Wind resistance. Wall coverings, backing materials and their attachments shall be capable of resisting wind loads in accordance with Tables R301.2.1(1) and R301.2.1(2). Wind-pressure resistance of the siding, exterior soffit and backing materials shall be determined by ASTM E330 or other applicable standard test methods. Where wind-pressure resistance is determined by design analysis, data from approved design standards and analysis conforming to generally accepted engineering practice shall be used to evaluate the siding, exterior soffit and backing material and its fastening. All applicable failure modes including bending rupture of siding, fastener withdrawal and fastener head pull-through shall be considered in the testing or design analysis. Where the wall covering, exterior soffit and backing material resist wind load as an assembly, use of the design capacity of the assembly shall be permitted. R703.2 Water-resistive barrier. Not fewer than one layer of water-resistive barrier shall be applied over studs or sheathing of all exterior walls with flashing as indicated in Section R703.4, in such a manner as to provide a continuous water-resistive barrier behind the exterior wall veneer and behind deck ledgers. The water-resistive barrier material shall be continuous to the top of walls and terminated at penetrations and building appendages in a manner to meet the requirements of the exterior wall envelope as described in Section R703.1. Where the water-resistive barrier also functions as a component of a continuous air barrier, the waterresistive barrier shall be installed as an air barrier in accordance with Section N1102.5.1.1. Water-resistive barrier materials shall comply with one of the following:
1. No. 15 felt complying with ASTM D226, Type 1.
2. ASTM E2556, Type 1 or 2.
3. Foam plastic insulating sheathing water-resistive barrier systems complying with Section R703.1.1 and installed in accordance with the manufacturer’s installation instructions.
4. ASTM E331 in accordance with Section R703.1.1.
5. Other approved materials in accordance with the manufacturer’s installation instructions. No.15 asphalt felt and water-resistive barriers complying with ASTM E2556 shall be applied horizontally, with the upper layer lapped over the lower layer not less than 2 inches (51 mm), and where joints occur, shall be lapped not less than 6 inches (152 mm). Exception: A water-resistive barrier shall not be required in unconditioned detached tool sheds, storage sheds, playhouses, and other similar accessory structures provided all of the following requirements are met:
6. Exterior wall covering is limited to siding that is attached direct to studs.
7. Exterior walls are uninsulated.
8. Interior side of exterior walls has no wall covering or wall finishes. R703.3 Wall covering nominal thickness and attachments. The nominal thickness and attachment of exterior wall coverings shall be in accordance with Table R703.3(1), the wall covering material requirements of this section, and the wall covering manufacturer’s installation instructions. Cladding attachment over foam sheathing shall comply with the additional requirements and limitations of Sections R703.15 through R703.17.
CRC § 6.4 High relevance — show source text
Exceptions:
1. Where a window or door opening is located less than 2 inches (51 mm) above the ledger, flashing shall extend to the bottom of the wall opening.
2. Flashing is not required where the ledger is spaced horizontally from the exterior wall covering not less than [1] / 4 inch (6.4 mm) to allow for drainage and ventilation behind the ledger.
R507.9.1.6 Water-resistive barrier. The water-resistive barrier required by Section R703.2 shall be lapped over a vertical leg of the ledger flashing or counterflashing extending up the wall by not less than 2 inches (51 mm) or the height of the vertical flashing leg, whichever is less. The water-resistive barrier shall continue from the top of the ledger flashing down the wall and behind the ledger flashing and ledger.

Exceptions:
1. Flashing shall be permitted to be placed against the face of the water-resistive barrier where a self-adhering membrane counterflashing is installed not less than 2 inches (51 mm) over the vertical leg of the flashing and not less than 2 inches (51 mm) onto the water-resistive barrier.
2. Flashing shall be permitted to be placed in front of the water-resistive barrier and behind the exterior wall covering where ledgers are spaced horizontally from the exterior wall not less than [1] / 4 inch (6.4 mm) to allow for drainage and ventilation behind the ledger.
R507.9.1.7 Existing walls. Where ledgers are attached to existing walls without water-resistive barriers, a water-resistive barrier shall be installed behind the ledger and ledger flashing. The water-resistive barrier shall extend to the top of the ledger flashing vertical leg and not less than [1] / 2 inch (12.7 mm) beyond the sides and bottom of the ledger. A self-adhering membrane counterflashing shall be installed not less than 2 inches (51 mm) over the vertical leg of the ledger flashing and not less than 2 inches (51 mm) onto the existing sheathing.

Exceptions:
1. Where a window or door opening is located less than 2 inches (51 mm) above the ledger, flashing shall extend to the bottom of the wall opening.
2. Flashing is not required where the ledger is spaced horizontally from the exterior wall covering not less than [1] / 4 inch (6.4 mm) to allow for drainage and ventilation behind the ledger.
R507.9.1.8 Exterior wall coverings. Exterior wall coverings shall be terminated above the finished deck surface in accordance with the covering manufacturer’s requirements and Chapter 7, as applicable to the type of covering.

Exception: Exterior wall coverings shall be permitted behind ledgers in accordance with Section R507.9.1.5 where capable of resisting compression forces from the ledger attachment.
CRC § 1.1 High relevance — show source text
R703.1 General. Exterior walls shall provide the building with a weather-resistant exterior wall envelope. The exterior wall envelope shall include flashing as described in Section R703.4. Exception: Log walls designed and constructed in accordance with the provisions of ICC 400. R703.1.1 Water resistance. The exterior wall envelope shall be designed and constructed in a manner that prevents the accumulation of water within the wall assembly by providing a water-resistive barrier behind the exterior cladding as required by Section R703.2 and a means of draining to the exterior water that penetrates the exterior cladding. Exceptions:
1. A weather-resistant exterior wall envelope shall not be required over concrete or masonry walls designed in accordance with Chapter 6 and flashed in accordance with Section R703.4 or R703.8.
2. Compliance with the requirements for a means of drainage, and the requirements of Sections R703.2 and R703.4, shall not be required for an exterior wall envelope that has been demonstrated to resist wind-driven rain through testing of the exterior wall envelope, including joints, penetrations and intersections with dissimilar materials, in accordance with ASTM E331 under the following conditions: 2.1. Exterior wall envelope test assemblies shall include at least one opening, one control joint, one wall/eave interface and one wall sill. All tested openings and penetrations shall be representative of the intended enduse configuration. 2.2. Exterior wall envelope test assemblies shall be at least 4 feet by 8 feet (1219 mm by 2438 mm) in size. 2.3. Exterior wall assemblies shall be tested at a minimum differential pressure of 6.24 pounds per square foot (299 Pa). 2.4. Exterior wall envelope assemblies shall be subjected to the minimum test exposure for a minimum of 2 hours. The exterior wall envelope design shall be considered to resist wind-driven rain where the results of testing indicate that water did not penetrate control joints in the exterior wall envelope, joints at the perimeter of openings penetration or intersections of terminations with dissimilar materials.
R703.1.2 Wind resistance. Wall coverings, backing materials and their attachments shall be capable of resisting wind loads in accordance with Tables R301.2.1(1) and R301.2.1(2). Wind-pressure resistance of the siding, exterior soffit and backing materials shall be determined by ASTM E330 or other applicable standard test methods. Where wind-pressure resistance is determined by design analysis, data from approved design standards and analysis conforming to generally accepted engineering practice shall be used to evaluate the siding, exterior soffit and backing material and its fastening. All applicable failure modes including bending rupture of siding, fastener withdrawal and fastener head pull-through shall be considered in the testing or design analysis. Where the wall covering, exterior soffit and backing material resist wind load as an assembly, use of the design capacity of the assembly shall be permitted. R703.2 Water-resistive barrier. Not fewer than one layer of water-resistive barrier shall be applied over studs or sheathing of all exterior walls with flashing as indicated in Section R703.4, in such a manner as to provide a continuous water-resistive barrier behind the exterior wall veneer and behind deck ledgers. The water-resistive barrier material shall be continuous to the top of walls and terminated at penetrations and building appendages in a manner to meet the requirements of the exterior wall envelope as described in Section R703.1.
CRC § 7-9 High relevance — show source text
4, 5, 6,_
9, 12, 16|Includes Mendocino, Sonoma, Marin, San Francisco, San Mateo, Alameda, Santa Cruz, Monterey, San Benito,
San Luis Obispo, Santa Barbara, Ventura, San Diego Counties| |_2 _|14, 16|Includes Imperial County| |a. IECC Climate Zones 1, 7 and 8 do not occur in California, nor do any IECC moist climate zones.
b. IECC boundaries are defined by county political boundary lines. California Energy Code boundaries are based on metes and bounds specifications aligned with climate-affecting
geographic features, which often do not coincide with county lines.|a. IECC Climate Zones 1, 7 and 8 do not occur in California, nor do any IECC moist climate zones.
b. IECC boundaries are defined by county political boundary lines. California Energy Code boundaries are based on metes and bounds specifications aligned with climate-affecting
geographic features, which often do not coincide with county lines.|a. IECC Climate Zones 1, 7 and 8 do not occur in California, nor do any IECC moist climate zones.
b. IECC boundaries are defined by county political boundary lines. California Energy Code boundaries are based on metes and bounds specifications aligned with climate-affecting
geographic features, which often do not coincide with county lines.|

2025 CALIFORNIA RESIDENTIAL CODE 7-9

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

WALL COVERING

SECTION R703—EXTERIOR WALL COVERING

R703.1 General. Exterior walls shall provide the building with a weather-resistant exterior wall envelope. The exterior wall envelope shall include flashing as described in Section R703.4. Exception: Log walls designed and constructed in accordance with the provisions of ICC 400. R703.1.1 Water resistance. The exterior wall envelope shall be designed and constructed in a manner that prevents the accumulation of water within the wall assembly by providing a water-resistive barrier behind the exterior cladding as required by Section R703.2 and a means of draining to the exterior water that penetrates the exterior cladding. Exceptions:
1. A weather-resistant exterior wall envelope shall not be required over concrete or masonry walls designed in accordance with Chapter 6 and flashed in accordance with Section R703.4 or R703.8.
2. Compliance with the requirements for a means of drainage, and the requirements of Sections R703.2 and R703.4, shall not be required for an exterior wall envelope that has been demonstrated to resist wind-driven rain through testing of the exterior wall envelope, including joints, penetrations and intersections with dissimilar materials, in accordance with ASTM E331 under the following conditions: 2.1. Exterior wall envelope test assemblies shall include at least one opening, one control joint, one wall/eave interface and one wall sill. All tested openings and penetrations shall be representative of the intended enduse configuration. 2.2. Exterior wall envelope test assemblies shall be at least 4 feet by 8 feet (1219 mm by 2438 mm) in size. 2.3. Exterior wall assemblies shall be tested at a minimum differential pressure of 6.24 pounds per square foot (299 Pa). 2.4. Exterior wall envelope assemblies shall be subjected to the minimum test exposure for a minimum of 2 hours.
CRC § 1401.1 High relevance — show source text
ICC code development note: Code change proposals to sections preceded by the designation [BS] will be considered by the IBC—Structural Code Development

Committee during the 2025 (Group B) Code Development Cycle.

SECTION 1401—GENERAL

1401.1 Scope. The provisions of this chapter shall establish the minimum requirements for exterior walls, exterior wall assemblies, exterior wall coverings, exterior wall openings, exterior windows and doors, exterior soffits and fascias, and architectural trim.

SECTION 1402—PERFORMANCE REQUIREMENTS

1402.1 General. The provisions of this section shall apply to exterior walls, exterior wall coverings and components thereof.

1402.2 Weather protection. Buildings shall be provided with a weather-resistant exterior wall assembly. The exterior wall assembly shall include flashing, as described in Section 1404.4. The exterior wall assembly shall be designed and constructed in such a manner as to prevent the accumulation of water within the exterior wall assembly by providing a water-resistive barrier behind the exterior veneer, as described in Section 1403.2, and a means for draining water that enters the assembly to the exterior. Protection against condensation in the exterior wall assembly shall be provided in accordance with Section 1404.3.

Exceptions:
1. A weather-resistant exterior wall assembly shall not be required over concrete or masonry walls designed in accordance with Chapters 19 and 21, respectively.
2. Compliance with the requirements for a means of drainage, and the requirements of Sections 1403.2 and 1404.4, shall not be required for an exterior wall assembly that has been demonstrated through testing to resist wind-driven rain, including joints, penetrations and intersections with dissimilar materials, in accordance with ASTM E331 under the following conditions:
The exterior wall design shall be considered to resist wind-driven rain where the results of testing, in accordance with ASTM E331, indicate that water did not penetrate control joints in the exterior wall, joints at the perimeter of openings or intersections of terminations with dissimilar materials.

2.1. Exterior wall test assemblies shall include not fewer than one opening, one control joint, one wall/eave interface and one wall sill. Tested openings and penetrations shall be representative of the intended end-use configuration. 2.2. Exterior wall test assemblies shall be not less than 4 feet by 8 feet (1219 mm by 2438 mm) in size. 2.3. Exterior wall test assemblies shall be tested at a minimum differential pressure of 6.24 pounds per square foot (0.297 kN/m [2] ). 2.4. Exterior wall test assemblies shall be subjected to a minimum test exposure duration of 2 hours. 3. Exterior insulation and finish systems (EIFS) complying with Section 1407.4.1.

1402.2.1 [BSC-CG] See California Green Building Standards Code, Chapter 5, Division 5.4 for additional weather protection requirements.

[BS] 1402.3 Wind resistance. Exterior walls, exterior wall coverings, exterior soffits and fascias, and the associated openings, shall be designed and constructed to resist safely the superimposed loads required by Chapter 16.
CRC § 7.3 High relevance — show source text
** In Dry (B) climate zones indicated in Section R702.7.3 and Table R702.7.3, water-resistive barriers shall comply with one of the following:
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 a 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. Flashing installed in accordance with Section R703.4 and intended to drain to the water-resistive barrier shall be 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 a 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, other non-water-absorbing layer, a drainage space or means of drainage complying with Section R703.7.3.2. Flashing installed in accordance with Section 703.4 and intended to drain to the water-resistive barrier shall be directed to the exterior side of the water-resistive barrier.
R703.7.3.2 Moist or marine climates. In the Moist (A) or Marine (C) climate zones indicated in Section R702.7.3 and Table R702.7.3, water-resistive barriers shall comply with one of the following:
1. In addition to complying with Section R703.7.3.1, a space or drainage material not less than [3] / 16 inch (5 mm) in depth shall be added to the exterior side of the water-resistive barrier.
2. In addition to complying with Section R703.7.3.1, Item 2, drainage on the exterior of the water-resistive barrier shall have a drainage efficiency of not less than 90 percent, as measured in accordance with ASTM E2273 or Annex A2 of ASTM E2925.
R703.7.4 Application. Each coat shall be kept in a moist condition for at least 48 hours prior to application of the next coat.

Exception: Applications installed in accordance with ASTM C926.

R703.7.5 Curing. The finish coat for two-coat cement plaster shall not be applied sooner than seven days after application of the first coat. For three-coat cement plaster, the second coat shall not be applied sooner than 48 hours after application of the first coat. The finish coat for three-coat cement plaster shall not be applied sooner than seven days after application of the second coat.

R703.8 Anchored stone and masonry veneer, general. Anchored stone and masonry veneer shall be installed in accordance with this chapter, Table R703.3(1) and Figures R703.8(1) and R703.8(2). These veneers installed over a backing of wood or cold-formed steel shall be limited to the first story above grade plane and shall not exceed 5 inches (127 mm) in thickness. See Section R602.10 for wall bracing requirements for masonry veneer for wood-framed construction and Section R603.9.5 for wall bracing requirements for masonry veneer for cold-formed steel construction.
CRC § 7.2.1 High relevance — show source text
On wood-frame construction with an on-grade floor slab system, exterior plaster shall be applied to cover, but not extend below, lath, paper and screed.

The proportion of aggregate to cementitious materials shall be as set forth in Table R702.1(3).

R703.7.2.1 Weep screeds. A minimum 0.019-inch (0.5 mm) (No. 26 galvanized sheet gage), corrosion-resistant weep screed or plastic weep screed, with a minimum vertical attachment flange of 3 [1] / 2 inches (89 mm), shall be provided at or below the foundation plate line on exterior stud walls in accordance with ASTM C926. The weep screed shall be placed not less than 4 inches (102 mm) above the earth or 2 inches (51 mm) above paved areas and shall be of a type that will allow trapped water to drain to the exterior of the building. The weather-resistant barrier shall lap the attachment flange. The exterior lath shall cover and terminate on the attachment flange of the weep screed.

R703.7.3 Water-resistive barriers. Water-resistive barriers shall be installed as required in Section R703.2 and shall comply with Section R703.7.3.1 or R703.7.3.2.

Exception: Sections R703.7.3.1 and R703.7.3.2 shall not apply to construction where accumulation, condensation or freezing of moisture will not damage the materials.

R703.7.3.1 Dry climates. In Dry (B) climate zones indicated in Section R702.7.3 and Table R702.7.3, water-resistive barriers shall comply with one of the following:
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 a 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. Flashing installed in accordance with Section R703.4 and intended to drain to the water-resistive barrier shall be 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 a 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, other non-water-absorbing layer, a drainage space or means of drainage complying with Section R703.7.3.2. Flashing installed in accordance with Section 703.4 and intended to drain to the water-resistive barrier shall be directed to the exterior side of the water-resistive barrier.
R703.7.3.2 Moist or marine climates. In the Moist (A) or Marine (C) climate zones indicated in Section R702.7.3 and Table R702.7.3, water-resistive barriers shall comply with one of the following:
1. In addition to complying with Section R703.7.3.1, a space or drainage material not less than [3] / 16 inch (5 mm) in depth shall be added to the exterior side of the water-resistive barrier.
CRC § 2025 High relevance — show source text
The prescriptive provisions of this chapter provide requirements for constructing footings and walls for foundations of wood, masonry, concrete and precast concrete. In addition to a foundation’s ability to support the required design loads, this chapter addresses several other factors that can affect foundation performance. These include controlling surface water and subsurface drainage, requiring soil tests where conditions warrant and evaluating proximity to slopes and minimum depth requirements. The chapter also provides requirements to minimize adverse effects of moisture, decay and pests in basements and crawl spaces.

Chapter 5 Floors.

Chapter 5 provides the requirements for the design and construction of floor systems that will be capable of supporting minimum required design loads. This chapter covers four different types: wood floor framing, wood floors on the ground, cold-formed steel floor framing and concrete slabs on the ground. Allowable span tables are provided that greatly simplify the determination of joist, girder and sheathing sizes for raised floor systems of wood framing and cold-formed steel framing. This chapter also contains prescriptive requirements for wood-framed exterior decks and their attachment to the main building.

Chapter 6 Wall Construction.

Chapter 6 contains provisions that regulate the design and construction of walls. The wall construction covered in Chapter 6 consists of five different types: wood framed, cold-formed steel framed, masonry, concrete and structural insulated panel (SIP). The primary concern of this chapter is the structural integrity of wall construction and transfer of all imposed loads to the supporting structure. This chapter provides the requirements for the design and construction of wall systems that are capable of supporting the minimum design vertical loads (dead, live and snow loads) and lateral loads (wind or seismic loads). This chapter contains the prescriptive requirements for wall bracing and/or shear walls to resist the imposed lateral loads due to wind and seismic activity.

Chapter 6 also regulates exterior windows and doors installed in walls. This chapter contains criteria for the performance of exterior windows and doors and includes provisions for testing and labeling, garage doors, windborne debris protection and anchorage details.

Chapter 7 Wall Covering.

Chapter 7 contains provisions for the design and construction of interior and exterior wall coverings. This chapter establishes the various types of materials, materials standards and methods of application permitted for use as interior coverings, including interior plaster, gypsum board, ceramic tile, wood veneer paneling, hardboard paneling, wood shakes and wood shingles. Chapter 7 also contains requirements for the use of vapor retarders for moisture control in walls.

2025 CALIFORNIA RESIDENTIAL CODE xv

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

Exterior wall coverings provide the weather-resistant exterior envelope that protects the building’s interior from the elements. Chapter 7 provides the requirements for wind resistance and water-resistive barrier for exterior wall coverings. This chapter prescribes the exterior wall coverings as well as the water-resistive barrier required beneath the exterior materials. Exterior wall coverings regulated by this section include aluminum, stone and masonry veneer, wood, hardboard, particleboard, wood structural panel siding, wood shakes and shingles, exterior plaster, steel, vinyl, fiber cement and exterior insulation finish systems.

Chapter 8 Roof-Ceiling Construction.
CRC § 2025 High relevance — show source text
Chapter 6 also regulates exterior windows and doors installed in walls. This chapter contains criteria for the performance of exterior windows and doors and includes provisions for testing and labeling, garage doors, windborne debris protection and anchorage details.

Chapter 7 Wall Covering.

Chapter 7 contains provisions for the design and construction of interior and exterior wall coverings. This chapter establishes the various types of materials, materials standards and methods of application permitted for use as interior coverings, including interior plaster, gypsum board, ceramic tile, wood veneer paneling, hardboard paneling, wood shakes and wood shingles. Chapter 7 also contains requirements for the use of vapor retarders for moisture control in walls.

2025 CALIFORNIA RESIDENTIAL CODE xv

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

Exterior wall coverings provide the weather-resistant exterior envelope that protects the building’s interior from the elements. Chapter 7 provides the requirements for wind resistance and water-resistive barrier for exterior wall coverings. This chapter prescribes the exterior wall coverings as well as the water-resistive barrier required beneath the exterior materials. Exterior wall coverings regulated by this section include aluminum, stone and masonry veneer, wood, hardboard, particleboard, wood structural panel siding, wood shakes and shingles, exterior plaster, steel, vinyl, fiber cement and exterior insulation finish systems.

Chapter 8 Roof-Ceiling Construction.

Chapter 8 regulates the design and construction of roof-ceiling systems. This chapter contains two roof-ceiling framing systems: wood framing and cold-formed steel framing. Allowable span tables are provided to simplify the selection of rafter and ceiling joist size for wood roof framing and cold-formed steel framing. Chapter 8 also provides requirements for the application of ceiling finishes, the proper ventilation of concealed spaces in roofs (e.g., enclosed attics and rafter spaces), unvented attic assemblies and attic access.

Chapter 9 Roof Assemblies.

Chapter 9 regulates the design and construction of roof assemblies. A roof assembly includes the roof deck, vapor retarder, substrate or thermal barrier, insulation, vapor retarder and roof covering. This chapter provides the requirement for wind resistance of roof coverings.

The types of roof covering materials and installation regulated by Chapter 9 are: asphalt shingles, clay and concrete tile, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shakes and shingles, built-up roofs, metal roof panels, modified bitumen roofing, thermoset and thermoplastic single-ply roofing, sprayed polyurethane foam roofing, liquid applied coatings and photovoltaic shingles. Chapter 9 also provides requirements for roof drainage, flashing, above deck thermal insulation, rooftop-mounted photovoltaic systems and recovering or replacing an existing roof covering.

Chapter 10 Chimneys and Fireplaces.

Chapter 10 contains requirements for the safe construction of masonry chimneys and fireplaces and establishes the standards for the use and installation of factory-built chimneys, fireplaces and masonry heaters. Chimneys and fireplaces constructed of masonry rely on prescriptive requirements for the details of their construction; the factory-built type relies on the listing and labeling method of approval. Chapter 10 provides the requirements for seismic reinforcing and anchorage of masonry fireplaces and chimneys.

Chapter 11 [RE] Energy Efficiency.

Chapter 11 is not adopted in California. See California Energy Code, Title 24, Part 6.

Chapter 12 Mechanical Administration.
CRC § 4.1 High relevance — show source text
BK105.4.1 Water-resistive barriers and vapor permeance. Cob walls shall be constructed without a membrane barrier, except as otherwise required elsewhere in this appendix. Where a water-resistive barrier is placed behind an exterior finish, it shall be considered part of the finish system and shall comply with Item 2 of Section BK104.1.2 for the combined vapor permeance rating.

BK105.4.2 Horizontal surfaces. Cob walls and other cob elements shall be provided with a water-resistive barrier at weatherexposed horizontal surfaces. The water-resistive barrier shall be of a material and installation that will prevent erosion and prevent water from entering the wall system. Horizontal surfaces, including exterior windowsills, sills at exterior niches and exterior buttresses, shall be sloped not less than 1 unit vertical in 12 units horizontal to drain away from cob walls or other cob elements.

BK105.4.3 Separation of cob and foundation. A liquid-applied or bituminous Class II vapor retarder shall be installed between cob and supporting concrete or masonry.

Exception: Where local climate, site conditions and foundation design limit ground moisture migration into the base of the cob wall, including but not limited to the use of a moisture barrier or capillary break between the supporting concrete or masonry and the earth.

BK105.4.4 Separation of cob and finished grade. Cob shall be not less than 8 inches (203 mm) above finished grade.

Exception: The minimum separation shall be 4 inches (102 mm) in dry climate zones, as defined in Section R702.7.3 and Table R702.7.3, and shall be 2 inches (51mm) on walls that are not weather exposed.

BK105.4.5 Installation of windows and doors. Windows and doors shall be installed in accordance with the manufacturer’s instructions to a wooden buck of not less than nominal 2-inch by 4-inch (51 mm by 102 mm) wood members. The installation of windows and doors and their bucks shall prevent the passage of air and water into or through the wall system. Windowsills shall comply with Section BK105.4.2.

Window and door bucks shall be installed in accordance with Figure BK105.4.5 and one of the following methods:
1. Side members of the bucks shall be anchored into the cob wall by embedding the protruding end of half-driven 16d galvanized nails at a maximum 6-inch (152 mm) spacing. The buck shall be embedded into the cob not less than 1½ inches (38 mm) and set in from each face of the wall not less than 3 inches (76 mm).
2. Wood stiffeners not less than nominal 2-inch by 4-inch (51 mm by 102 mm) shall be attached on-edge to the sides of the buck and embedded in the cob wall a minimum of 3½ inches (89 mm). Stiffeners shall anchor into the cob wall with the protruding end of half-driven 16d galvanized nails at a maximum 6-inch (152 mm) spacing. Stiffeners shall be set back not less than 3 inches (76 mm) from each wall face. Bucks are permitted to be exposed and do not require anchoring nails where stiffeners are used with this method.
3. Other approved methods satisfying the performance requirements of Section BK105.4.5.
Exception: Windows and unframed glass shall be permitted to be embedded directly into a cob wall with an approved design.

2025 CALIFORNIA RESIDENTIAL CODE APPENDIX BK-7
CRC § 9.1.3 High relevance — show source text
Lag screws or bolts shall be staggered from the top to the bottom along the horizontal run of the deck ledger in accordance with Figure R507.9.1.3(1).
b. Maximum 5 inches.
c. For engineered rim joists, the manufacturer’s recommendations shall govern.
d. The minimum distance from bottom row of lag screws or bolts to the top edge of the ledger shall be in accordance with Figure R507.9.1.3(1).|

FIGURE R507.9.1.3(2)—PLACEMENT OF LAG SCREWS AND BOLTS IN BAND JOISTS

"L" FLASHING (SHOWN) OR "Z" FLASHING (OPTIONAL)

LAG SCREWS OR BOLTS STAGGERED

APPROVED JOIST HANGER

For SI: 1 inch = 25.4 mm.

2025 CALIFORNIA RESIDENTIAL CODE 5-41

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

FLOORS

R507.9.1.4 Alternate ledger details. Alternate framing configurations supporting a ledger constructed to meet the load requirements of Section R301.5 shall be permitted.

R507.9.1.5 Ledger flashing. Where ledgers are attached to wood-frame construction, flashing shall be installed above the ledger to prevent the entry of water into the wall cavity or behind the ledger. Flashing shall extend vertically not less than 2 inches (51 mm) above the ledger. Flashing shall extend horizontally not less than 4 inches (102 mm) beyond the ledger face or shall extend to the ledger face and not less than [1] / 4 inch down the ledger face.

Exceptions:
1. Where a window or door opening is located less than 2 inches (51 mm) above the ledger, flashing shall extend to the bottom of the wall opening.
2. Flashing is not required where the ledger is spaced horizontally from the exterior wall covering not less than [1] / 4 inch (6.4 mm) to allow for drainage and ventilation behind the ledger.
R507.9.1.6 Water-resistive barrier. The water-resistive barrier required by Section R703.2 shall be lapped over a vertical leg of the ledger flashing or counterflashing extending up the wall by not less than 2 inches (51 mm) or the height of the vertical flashing leg, whichever is less. The water-resistive barrier shall continue from the top of the ledger flashing down the wall and behind the ledger flashing and ledger.

Exceptions:
1. Flashing shall be permitted to be placed against the face of the water-resistive barrier where a self-adhering membrane counterflashing is installed not less than 2 inches (51 mm) over the vertical leg of the flashing and not less than 2 inches (51 mm) onto the water-resistive barrier.
2. Flashing shall be permitted to be placed in front of the water-resistive barrier and behind the exterior wall covering where ledgers are spaced horizontally from the exterior wall not less than [1] / 4 inch (6.4 mm) to allow for drainage and ventilation behind the ledger.
CRC § 1402.6 High relevance — show source text
1402.6 Water-resistive barriers. Exterior walls on buildings of Type I, II, III or IV construction that are greater than 40 feet (12 192 mm) in height above grade plane and contain a combustible water-resistive barrier shall be tested in accordance with and comply with the acceptance criteria of NFPA 285.Combustibility shall be determined in accordance with Section 703.3. For the purposes of this section, fenestration products, flashing of fenestration products and water-resistive-barrier flashing and accessories at other locations, including through wall flashings, shall not be considered part of the water-resistive barrier.

Exceptions:
1. Exterior walls in which the water-resistive barrier is the only combustible component and the exterior wall has an exterior wall covering of brick, concrete, stone, terra cotta, stucco or steel with minimum thicknesses in accordance with Table 1404.2.
2. Exterior walls in which the water-resistive barrier is the only combustible component and the water-resistive barrier complies with the following: 2.1 A peak heat release rate of less than 150 kW/m [2], a total heat release of less than 20 MJ/m [2] and an effective heat of combustion of less than 18 MJ/kg when tested on specimens at the thickness intended for use, in accordance with ASTM E1354, in the horizontal orientation and at an incident radiant heat flux of 50 kW/m [2] .
2.2 A flame spread index of 25 or less and a smoke-developed index of 450 or less as determined in accordance with ASTM E84 or UL 723, with test specimen preparation and mounting in accordance with ASTM E2404.

1402.7 Exterior wall veneers manufactured using combustible adhesives. Exterior wall assemblies on buildings of Type I, II, III or IV construction that are greater than 40 feet (12 192 mm) in height above grade plane and contain an exterior wall veneer manufactured using a combustible adhesive to laminate a metal core with noncombustible facing materials shall be tested in accordance with, and comply with, the acceptance criteria of NFPA 285, with the adhesive level at the maximum application rate intended for use. Combustibility shall be determined in accordance with Section 703.3.

1402.8 Vertical and lateral flame propagation compliance methods. When exterior wall assemblies are required in this chapter to be tested for vertical and lateral flame propagation in accordance with and comply with the acceptance criteria of NFPA 285, compliance with the requirements shall be established by any of the following:
1. An exterior wall assembly tested in accordance with and meeting the acceptance criteria of NFPA 285.
2. An exterior wall assembly design listed by an approved agency for compliance with NFPA 285.
3. An approved analysis based on an assembly or condition tested in accordance with and meeting the acceptance criteria of NFPA 285.
[BS] 1402.9 Flood resistance. For buildings in flood hazard areas as established in Section 1612.3, exterior walls extending below the elevation required by Section 1612 shall be constructed with flood-damage-resistant materials.

[BS] 1402.10 Flood resistance for coastal high-hazard areas and coastal A zones. For buildings in coastal high-hazard areas and coastal A zones as established in Section 1612.3, electrical, mechanical and plumbing system components shall not be mounted on or penetrate through exterior walls that are designed to break away under flood loads.

SECTION 1403—MATERIALS

Frequently asked questions

Must every exterior wall have a WRB?

Yes — one continuous layer of WRB is required over studs or sheathing on all exterior walls unless the accessory structure exception applies (see § R703.2).

Can I use a peel‑and‑stick self‑adhesive membrane?

Only if it meets one of the code‑listed acceptance paths (ASTM E2556, ASTM E331, manufacturer/system approval, or other approved materials installed per the manufacturer) or is otherwise approved by the building official — see § R703.2.

How much must felt overlap at laps?

No. 15 felt and WRBs complying with ASTM E2556 applied horizontally require upper layer lap ≥ 2 in (51 mm) and end laps ≥ 6 in (152 mm), per § R703.2.

Are there extra requirements for stucco?

Yes — stucco WRB requirements vary by climate zone: two layers of 10‑minute Grade D paper in Dry zones, or other combinations requiring separation/drainage and in Moist/Marine zones a ≥ 3/16 in (5 mm) drainage space or ≥ 90% drainage efficiency (see § R703.7.3).

What about WRB at deck ledgers?

WRB must lap over the vertical leg of ledger flashing ≥ 2 in (51 mm) (or to the vertical leg height, whichever is less) and continue behind the ledger and flashing per § R507.9.1.6.

Ask about the CRC

Get cited, plain-English answers on the California Residential Code for your project — any code section, any scenario.

Start Free Trial

Related in the CRC

What nominal thickness and attachment rules apply to exterior wall coverings?

What are the CRC requirements for EIFS / exterior insulation and finish systems (EIFS)?

How must siding and cladding resist wind (tests, design methods)?

Exterior wall coverings & cladding (R703)

California Residential Code