CHBC · California Historical Building Code

What height‑to‑thickness ratios, bond beam and stability rules apply to adobe walls?

For a homeowner: the CHBC limits how tall an adobe wall can be relative to how thick it is — one‑story walls must be no taller than six times their thickness, and two‑story walls must be six times at the first floor and five times at the second. If a wall is taller than those limits you’ll need strengthening (commonly a bond beam) sized by an engineer and approved by the building department.

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Last reviewed: July 6, 2026

What the code requires — 2–4 sentences

The California Historical Building Code requires that unreinforced adobe load‑bearing walls meet specific height‑to‑thickness limits so they need not be evaluated for out‑of‑plane failure: one‑story walls ≤ a 6:1 height‑to‑thickness ratio; two‑story walls ≤ 6:1 at the ground floor and ≤ 5:1 at the second floor. Where walls do not meet those ratios, the CHBC says additional strengthening (for example, a bond beam) may be appropriate. These requirements are stated in § 8-806.3 and the bond‑beam/top‑of‑wall requirement is in § 8-806.5.

One clear rule: keep one‑story adobe walls at or below H:T = 6:1; two‑story walls must be H:T ≤ 6:1 at the first story and H:T ≤ 5:1 at the second story — otherwise provide strengthening such as a bond beam.

Requirements in detail

Height‑to‑thickness ratios (the heart of the rule)

  • One‑story load‑bearing adobe walls: maximum height‑to‑thickness ratio = 6 (that is, H ≤ 6 × T). § 8-806.3
  • Two‑story buildings/structures: measure the wall height at the floor‑to‑floor elevation. Limits are H:T ≤ 6 at the ground floor and H:T ≤ 5 at the second floor. § 8-806.3
  • The CHBC treats existing sod or rammed earth walls similarly where these provisions apply. § 8-806.3

Note: the CHBC text ties the second‑floor ratio measurement to the condition “when the second floor and attic ceiling/roof are connected to the wall as described below” — so measurement and restraint conditions are linked in the rule. § 8-806.3

Nonload‑bearing walls and partitions

  • Nonload‑bearing adobe partitions and gable end walls must be evaluated for stability and anchored against out‑of‑plane failure if necessary. The CHBC does not give a single numeric threshold for all nonload‑bearing walls — evaluation and anchorage are required where stability is a concern. § 8-806.4

Bond beam (location and performance requirement)

  • When provided, a bond beam or equivalent horizontal structural element must be located at the top of all adobe walls, and at the second floor for two‑story buildings/structures. § 8-806.5
  • The CHBC requires the bond beam’s size and configuration to be sufficient to brace the wall, tie the building together, and connect the wall to the floor or roof — but it does not prescribe numeric dimensions or reinforcement details in § 8-806.5. § 8-806.5

How the CHBC treats walls that don't meet the ratios

  • The CHBC says unreinforced adobe walls that meet the stated H:T criteria need not be evaluated for out‑of‑plane failure; where existing dimensions do not meet those conditions, additional strengthening measures, such as a bond beam, may be appropriate. § 8-806.3

Quick reference table (decision‑relevant)

Decision item Value / test Code Reference
One‑story load‑bearing H:T limit 6:1 (H ≤ 6 × T) § 8-806.3
Two‑story — ground floor H:T limit 6:1 (measured floor‑to‑floor) § 8-806.3
Two‑story — second floor H:T limit 5:1 (measured floor‑to‑floor when second floor & attic/roof connected to wall) § 8-806.3
Nonload‑bearing partitions & gable ends Must be evaluated for stability and anchored against out‑of‑plane failure if necessary § 8-806.4
Bond beam location requirement Top of all adobe walls; at second floor for two‑story § 8-806.5
Bond beam sizing CHBC: “sufficient to provide an effective brace…tie the building together…connect to floor or roof” (no numeric sizes in § 8-806.5) § 8-806.5

Exceptions & special cases

  • The CHBC allows alternative approaches that provide equivalent or greater safety, subject to the concurrence of the enforcing agency; do not assume fixed numeric workarounds without approval. § 8-806.1
  • Where walls do not meet H:T criteria, the CHBC explicitly contemplates additional strengthening measures (e.g., bond beams). The code does not mandate a single retrofit method — the chosen method must provide adequate bracing. § 8-806.3 and § 8-806.5
  • The CHBC treats sod or rammed earth similarly “to the extent these provisions apply” — verify applicability for non‑adobe earthen walls. § 8-806.3

If you need prescribed bond‑beam dimensions or reinforcement schedules, the CHBC text in § 8-806.5 does not provide numeric sizes; a registered design professional (or the enforcing agency) must determine appropriate sizing and detailing.

Common mistakes

  • Assuming the CHBC gives numeric bond‑beam sizes. It does not — § 8-806.5 requires adequacy, not specific dimensions. Always consult an RDP or the enforcing agency for sizing.
  • Measuring wall height incorrectly. For two‑story buildings the CHBC requires measurement at floor‑to‑floor height (and the second‑floor limit applies when the second floor and attic/roof are connected to the wall). § 8-806.3
  • Treating nonload‑bearing partitions as automatically safe — the code requires evaluation and anchorage if necessary. § 8-806.4
  • Applying regular CBC numeric limits for modern adobe details without checking the CHBC allowances for qualified historical structures and consulting the enforcing agency. § 8-801.1–8-801.3 (scope and intent) explain that historical methods may vary.

Worked example — applying the rule with numbers

Scenario: A two‑story historic adobe building with continuous load‑bearing adobe walls that are 24 inches thick (2.0 ft). Floor‑to‑floor: ground floor = 10 ft; second floor = 9 ft.

  1. Ground floor check: H:T limit at ground floor = 6:1 → allowed H = 6 × T = 6 × 2.0 ft = 12 ft. Actual ground floor H = 10 ft → OK under § 8-806.3.
  2. Second floor check: H:T limit at second floor = 5:1 → allowed H = 5 × 2.0 ft = 10 ft. Actual second floor H = 9 ft → OK under § 8-806.3.
  3. Bond beam: Because this is two‑story, the CHBC requires a bond beam at the second floor and at the top of walls (top of roof). Provide an engineered bond beam sufficient to brace the wall and tie floor/roof to the adobe per § 8-806.5.

If the second‑floor H were 12 ft instead of 9 ft, then H:T = 12 ÷ 2 = 6, which exceeds the second‑floor limit of 5:1; the CHBC says additional strengthening (e.g., bond beam, engineered retrofit) may be appropriate or required before the wall can be accepted without out‑of‑plane evaluation. § 8-806.3

Related provisions (CHBC)

  • § 8-806.1 — General (alternative approaches accepted with enforcing‑agency concurrence).
  • § 8-806.2 — Moisture protection (important for durability of adobe).
  • § 8-806.3 — Height‑to‑thickness ratio limits (controlling section).
  • § 8-806.4 — Nonload‑bearing adobe: evaluate and anchor for out‑of‑plane stability.
  • § 8-806.5 — Bond beam location and performance requirement (top of walls; at second floor).

Code references

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

  • CHBC § 8-805.3 High relevance — show source text

    8-805.3 Reconstructed walls. Totally reconstructed walls utilizing original brick or masonry, constructed similar to original, shall be constructed in accordance with the regular code. Repairs or infills may be constructed in a similar manner to the original walls without conforming to the regular code.

    SECTION 8-806 — ADOBE

    8-806.1 General. Unburned clay masonry may be constructed, reconstructed, stabilized or rehabilitated subject to this chapter. Alternative approaches which provide an equivalent or greater level of safety may be used, subject to the concurrence of the enforcing agency.

    8-806.2 Moisture protection. Provisions shall be in place to protect adobe structures from deterioration due to moisture penetration. Adobe shall be maintained in reasonably good condition. Particular attention shall be given to moisture content of adobe walls. Unmaintained walls or ruins shall be evaluated for safety based on their condition and stability. Additional protection measures may be appropriate subject to the concurrence of the enforcing agency.

    8-806.3 Height to thickness ratio. Unreinforced new or existing adobe walls meeting these criteria need not be evaluated for out of plane failure. Where existing dimensions do not meet these conditions, additional strengthening measures, such as a bond beam, may be appropriate. Existing sod or rammed earth walls shall be considered similar to the extent these provisions apply.

    1. One-story adobe load-bearing walls shall not exceed a height-to-thickness ratio of 6.
    2. Two-story adobe buildings or structures’ height- to-thickness wall ratio shall not exceed 6 at the ground floor and 5 at the second floor, and shall be measured at floor-to-floor height when the second floor and attic ceiling/roof are connected to the wall as described below.

    8-806.4 Nonload-bearing adobe. Nonload-bearing adobe partitions and gable end walls shall be evaluated for stability and anchored against out-of-plane failure if necessary.

    8-806.5 Bond beam. Where provided, a bond beam or equivalent structural element shall be located at the top of all adobe walls, and at the second floor for two-story buildings or structures. The size and configuration of the structural element shall be sufficient to provide an effective brace for the wall, to tie the building together and to connect the wall to the floor or roof.

    8-806.6 Repair or reconstruction. Repair or reconstruction of wall area may utilize unstabilized brick or adobe masonry designed to be compatible with the constituents of the existing adobe materials.

    8-806.7 Shear values. Existing adobe may be allowed a maximum strength level of 12 pounds per square inch (82.7 kPa) for shear.

    8-806.8 Mortar. Mortar may be of the same soil composition as that used in the existing wall, or in new walls as necessary to be compatible with the adobe brick.

    SECTION 8-807 — WOOD

    8-807.1 Existing wood diaphragms or walls. Existing wood diaphragms or walls of straight or diagonal sheathing shall be assigned shear resistance values appropriate with the fasteners and materials functioning in conjunction with the sheathing. The structural survey shall determine fastener details and spacings and verify a load path through floor construction. Shear values of Tables 8-8-A and 8-8-B.

    8-807.2 Wood lath and plaster. Wood lath and plaster walls and ceilings may be utilized using the shear values referenced in Section 8-807.1.

  • CHBC § 8-805.2 High relevance — show source text

    8-805.2 Stone masonry.

    8-805.2.1 Solid-backed stone masonry. Stone masonry solidly backed with brick masonry shall be treated as solid brick masonry as described in Section 8-805.1 and in the 2009 International Existing Building Code [®] (IEBC [®] ), provided representative testing and inspection verifies solid collar joints between stone and brick and that a reasonable number of stones lap with the brick wythes as headers or that steel anchors are present. Solid stone masonry where the wythes of stone effectively overlap to provide the equivalent header courses may also be treated as solid brick masonry.

    8-805.2.2 Independent wythe stone masonry. Stone masonry with independent face wythes may be treated as solid brick masonry as described in Section 8-805.1 and the CEBC, provided representative testing and inspection verify that the core is essentially solid in the masonry wall and that steel ties are epoxied in drilled holes between outer stone wythes at floors, roof and not to exceed 4 feet (1219 mm) on center in each direction, between floors and roof. A reinforcing element shall exist or be provided at or near the top of all stone masonry walls.

    2025 CALIFORNIA HISTORICAL BUILDING CODE 15

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    ARCHAIC MATERIALS AND METHODS OF CONSTRUCTION

    8-805.2.3 Testing of stone masonry. Testing of stone masonry shall be similar to the 2010 CEBC requirements for brick masonry, except that representative stones which are not interlocked shall be pulled outward from the wall and shear area appropriately calculated after the test.

    8-805.3 Reconstructed walls. Totally reconstructed walls utilizing original brick or masonry, constructed similar to original, shall be constructed in accordance with the regular code. Repairs or infills may be constructed in a similar manner to the original walls without conforming to the regular code.

    SECTION 8-806 — ADOBE

    8-806.1 General. Unburned clay masonry may be constructed, reconstructed, stabilized or rehabilitated subject to this chapter. Alternative approaches which provide an equivalent or greater level of safety may be used, subject to the concurrence of the enforcing agency.

    8-806.2 Moisture protection. Provisions shall be in place to protect adobe structures from deterioration due to moisture penetration. Adobe shall be maintained in reasonably good condition. Particular attention shall be given to moisture content of adobe walls. Unmaintained walls or ruins shall be evaluated for safety based on their condition and stability. Additional protection measures may be appropriate subject to the concurrence of the enforcing agency.

    8-806.3 Height to thickness ratio. Unreinforced new or existing adobe walls meeting these criteria need not be evaluated for out of plane failure. Where existing dimensions do not meet these conditions, additional strengthening measures, such as a bond beam, may be appropriate. Existing sod or rammed earth walls shall be considered similar to the extent these provisions apply.

    1. One-story adobe load-bearing walls shall not exceed a height-to-thickness ratio of 6.
    2. Two-story adobe buildings or structures’ height- to-thickness wall ratio shall not exceed 6 at the ground floor and 5 at the second floor, and shall be measured at floor-to-floor height when the second floor and attic ceiling/roof are connected to the wall as described below.
  • CHBC § 8-806.4 High relevance — show source text

    8-806.4 Nonload-bearing adobe. Nonload-bearing adobe partitions and gable end walls shall be evaluated for stability and anchored against out-of-plane failure if necessary.

    8-806.5 Bond beam. Where provided, a bond beam or equivalent structural element shall be located at the top of all adobe walls, and at the second floor for two-story buildings or structures. The size and configuration of the structural element shall be sufficient to provide an effective brace for the wall, to tie the building together and to connect the wall to the floor or roof.

    8-806.6 Repair or reconstruction. Repair or reconstruction of wall area may utilize unstabilized brick or adobe masonry designed to be compatible with the constituents of the existing adobe materials.

    8-806.7 Shear values. Existing adobe may be allowed a maximum strength level of 12 pounds per square inch (82.7 kPa) for shear.

    8-806.8 Mortar. Mortar may be of the same soil composition as that used in the existing wall, or in new walls as necessary to be compatible with the adobe brick.

    SECTION 8-807 — WOOD

    8-807.1 Existing wood diaphragms or walls. Existing wood diaphragms or walls of straight or diagonal sheathing shall be assigned shear resistance values appropriate with the fasteners and materials functioning in conjunction with the sheathing. The structural survey shall determine fastener details and spacings and verify a load path through floor construction. Shear values of Tables 8-8-A and 8-8-B.

    8-807.2 Wood lath and plaster. Wood lath and plaster walls and ceilings may be utilized using the shear values referenced in Section 8-807.1.

    8-807.3 Existing wood framing. Existing wood framing members may be assigned allowable stresses consistent with codes in effect at the time of construction. Existing or new replacement wood framing may be of archaic types originally used if properly researched, such as balloon and single wall. Wood joints such as dovetail and mortise and tenon types may be used structurally, provided they are well made. Lumber selected for use and type need not bear grade marks, and greater or lesser species such as low-level pine and fir, boxwood and indigenous hardwoods and other variations may be used for specific conditions where they were or would have been used.

    Wood fasteners such as square or cut nails may be used with a maximum increase of 50 percent over wire nails for shear.

    SECTION 8-808 — CONCRETE

    8-808.1 Materials. Natural cement concrete, unreinforced rubble concrete and similar materials may be utilized wherever that material is used historically. Concrete of low strength and with less reinforcement than required by the regular code may remain in place. The architect or engineer shall assign appropriate values of strength based on testing of samples of the materials. Bond and development lengths shall be determined based on historical information or tests.

    8-808.2 Detailing. The architect or engineer shall carefully evaluate all detailing provisions of the regular code which are not met and shall consider the implications of these variations on the ultimate performance of the structure, giving due consideration to ductility and reserve strength.

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    ARCHAIC MATERIALS AND METHODS OF CONSTRUCTION

    SECTION 8-809 — STEEL AND IRON

  • CHBC § 0.3 High relevance — show source text

    [BS] A113.8 Nonstructural masonry walls. Unreinforced masonry walls that do not carry design vertical or lateral loads and that are not required by the design to be part of the lateral force-resisting system shall be adequately anchored to new or existing supporting elements. The anchors and elements shall be designed for the out-of-plane forces specified in the building code. The height- or length-to-thickness ratio between such supporting elements for such walls shall not exceed nine.

    APPENDIX A-16 2025 CALIFORNIA EXISTING BUILDING CODE

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    APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

    [BS] A113.9 Truss and beam supports. Where trusses and beams other than rafters or joists are supported on masonry, independent secondary columns shall be installed to support vertical loads of the roof or floor members.

    Exception: Secondary supports are not required where S D1 is less than 0.3g.

    [BS] A113.10 Adjacent buildings. Where elements of adjacent buildings do not have a separation of 5 inches (127 mm) or greater, the allowable height-to-thickness ratios for “all other buildings” per Table A110.2 shall be used in the direction of consideration.

    SECTION A114—WALLS OF UNBURNED CLAY, ADOBE OR STONE MASONRY

    [BS] A114.1 General. Walls of unburned clay, adobe or stone masonry construction shall conform to the following:

    1. Walls of unburned clay, adobe or stone masonry shall not exceed a height- or length-to-thickness ratio specified in Table A114.1.

    2. Adobe shall be allowed a maximum value of 9 pounds per square inch (62.1 kPa) for shear unless higher values are justified by test.

    3. Mortar for repointing may be of the same soil composition and stabilization as the brick, in lieu of cement mortar.

    [BS]TABLE A114.1—MAXIMUM HEIGHT-TO-THICKNESS RATIO FOR ADOBE OR STONE WALLS Col2 Col3 Col4
    _SD_1 _SD_1 _SD_1
    0.13g ≤****_SD_1 < 0.25g 0.25g ≤****_SD_1 < 0.4g _SD_1 ≥ 0.4g
    One-story buildings 12 10 8
    Two-story buildings
    First story 14 11 9
    Second story 12 10 8

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    APPENDIX A-18 2025 CALIFORNIA EXISTING BUILDING CODE

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    CALIFORNIA EXISTING BUILDING CODE – MATRIX ADOPTION TABLE

    APPENDIX A

    CHAPTER A2 – EARTHQUAKE HAZARD REDUCTION IN EXISTING REINFORCED CONCRETE AND REINFORCED MASONRY WALL BUILDINGS WITH FLEXIBLE DIAPHRAGMS

  • CRC § 2025 High relevance — show source text
    TABLE BK106.11(1)—COB BRACED WALL PANEL TYPES Col2 Col3 Col4 Col5 Col6 Col7
    WALL TYPEa
    DESIGNATION    		 ANCHORS TO
    FOUNDATIONb    		 ANCHORS TO
    BOND BEAMc    		 VERTICAL STEEL
    REINFORCINGb, c    		 HORIZONTAL STEEL
    REINFORCING    		 MAXIMUM
    HEIGHT_H_d
    (in feet)    		 MAXIMUM
    ASPECT
    RATIO (H:L)
    A none 5/8″ threaded rod @ 12″;
    4″ from wall ends;
    12″ embedment in cob    		 none none 7e 1:1
    B #5 bar @ 12″;
    16″ embedment in cob    		 5/8″ threaded rod @ 12″;
    4″ from wall ends;
    16″ embedment in cob;
    2″ × 2″ ×1/4″ washer and
    nut at cob end    		 none 2″ × 2″ × 14 gage welded
    wire meshf @ 18″;
    6″ from foundation and
    bond beam    		 7e 1:1
    C #5 bar @ 12″;
    16″ embedment in cob    		 5/8″ threaded rod @ 12″;
    16″ embedment in cob    		 5/8″ threaded rod;
    4″ from each end of
    braced wall panel;
    continuous from founda-
    tion to bond beam    		 2″ × 2″ × 14 gage welded
    wire meshf @ 18″;
    6″ from foundation and
    bond beam    		 7e 2:1
    D (see vertical steel
    reinforcing)    		 (see vertical steel
    reinforcing)    		 5/8″ threaded rod;
    4″ from each end of
    braced wall panel and @
    12″; continuous from
    foundation to bond beam    		 2″ × 2″ × 14 gage welded
    wire meshf @ 18″;
    6″ from foundation and
    bond beam    		 7e 2:1

    APPENDIX BK-12 2025 CALIFORNIA RESIDENTIAL CODE

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    APPENDIX BK — COB CONSTRUCTION (MONOLITHIC ADOBE)

  • CHBC § 9.5. High relevance — show source text

    The maximum_H_ is the absolute limit or the limit based on wall thickness, whichever is more restrictive.
    c. Bond beams or other horizontal restraints are permitted to divide a wall into more than one unrestrained wall height with an approved engineered design.
    d._ T_= Cob wall thickness (in feet) at its minimum, without plaster.
    e.
    5/8-inch threaded rod anchors at prescribed spacing with 12-inch embedment in cob, full embedment in concrete bond beams or full penetration in wood bond beam with a
    nut and washer.
    f. Attach rafters to bond beam with 4-inch by 3-inch by 3-inch by 18-gage tension tie angles at prescribed spacing. See Figure BK106.9.5. Where rafters are attached to tension
    ties, roof sheathing shall be edge nailed.
    g. All walls shall be tested for compressive strength in accordance with Section BK106.6.
    h. For curved walls with an arc length (ARCc) to radius (Rc) ratio of 1.5:1 or greater, the_H_/ T factor shall be increased by 1, and the absolute height limit by 1 foot. See Section
    BK106.11.3.
    i.
    Wall type requires a modulus of rupture test in accordance with Section BK106.7.
    j.
    See wall Type A in Table BK106.11(1) for top anchor requirements.|

    APPENDIX BK-6 2025 CALIFORNIA RESIDENTIAL CODE

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    APPENDIX BK — COB CONSTRUCTION (MONOLITHIC ADOBE)

    BK105.3.1 Determination of out-of-plane loading. Out-of-plane loading for the use of Table BK105.3 shall be in accordance with the ultimate design wind speed and seismic design category requirements of Sections R301.2.1 and R301.2.2, respectively. An approved engineered design shall be required where the building is located in a special wind region or where wind design is required in accordance with Figure R301.2.1.1.

    BK105.3.2 Bond beams for nonstructural walls. Nonstructural cob walls shall be provided with a bond beam at the top of the wall that complies with Section BK106.9, except for requirements relating to roof and/or ceiling loads or braced wall panels.

    BK105.3.3 Lintels in nonstructural walls. Door, window and other openings in nonstructural cob walls shall require a lintel in accordance with Section BK106.10, except for requirements relating to roof and/or ceiling loads or braced wall panels.

    BK105.3.4 Reinforcing at wall openings. Reinforcing shall be installed at window, door, and similar wall openings and penetrations greater than 2 feet (610 mm) in width in accordance with Sections BK105.3.4.1 through BK105.3.4.3. Surface voids deeper than 25 percent of the wall thickness shall be considered an opening.

    BK105.3.4.1 Opening size limit. Openings shall not exceed 6 feet (1829 mm) in width, and the height of the cob wall below openings shall not exceed 6 feet (1829 mm) above the top of the foundation.

    **BK105.3.4.2 Horizontal reinforcing.

  • CHBC § 25.4 High relevance — show source text

    All braced wall panels shall be not
    greater than 24 inches thick.
    b. Not less than 8-inch embedment into foundation, unless otherwise stated.
    c. Not less than 4-inch embedment into concrete bond beams. Full penetration through wood bond beam, secured with nut and washer.
    d.H = height of the cob portion of the wall only. See Figure BK101.4.
    e. Maximum height shall be 8 feet when wall thickness is increased to 18 inches.
    f. Galvanized mesh.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
    a. Braced wall panel_T_ypes A, B, C and D shall be not less than 16 inches thick. Braced wall panel Type E shall be not less than 12 inches thick. All braced wall panels shall be not
    greater than 24 inches thick.
    b. Not less than 8-inch embedment into foundation, unless otherwise stated.
    c. Not less than 4-inch embedment into concrete bond beams. Full penetration through wood bond beam, secured with nut and washer.
    d.H = height of the cob portion of the wall only. See Figure BK101.4.
    e. Maximum height shall be 8 feet when wall thickness is increased to 18 inches.
    f. Galvanized mesh.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
    a. Braced wall panel_T_ypes A, B, C and D shall be not less than 16 inches thick. Braced wall panel Type E shall be not less than 12 inches thick. All braced wall panels shall be not
    greater than 24 inches thick.
    b. Not less than 8-inch embedment into foundation, unless otherwise stated.
    c. Not less than 4-inch embedment into concrete bond beams. Full penetration through wood bond beam, secured with nut and washer.
    d.H = height of the cob portion of the wall only. See Figure BK101.4.
    e. Maximum height shall be 8 feet when wall thickness is increased to 18 inches.
    f. Galvanized mesh.|

    TABLE BK106.11(2)—BRACING REQUIREMENTS FOR COB BRACED WALL PANELS BASED ON WIND SPEED Col2 Col3 Col4 Col5 Col6 Col7
    •
    EXPOSURE CATEGORY Bd
    •
    25-FOOT MEAN ROOF HEIGHT
    •
    10-FOOT EAVE-TO-RIDGE HEIGHTd
    •
    10-FOOT WALL HEIGHTd
    •
    2 BRACED WALL LINESd    		 •
    EXPOSURE CATEGORY Bd
    •
    25-FOOT MEAN ROOF HEIGHT
    •
    10-FOOT EAVE-TO-RIDGE HEIGHTd
    •
    10-FOOT WALL HEIGHTd
    •
    2 BRACED WALL LINESd    		 •
    EXPOSURE CATEGORY Bd
    •
    25-FOOT MEAN ROOF HEIGHT
    •
    **10-FOOT
  • CHBC § 1.5 High relevance — show source text

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    APPENDIX BK — COB CONSTRUCTION (MONOLITHIC ADOBE)

    TABLE BK106.11(3)—BRACING REQUIREMENTS FOR COB BRACED WALL PANELS BASED ON SEISMIC DESIGN CATEGORY A Col2 Col3 Col4 Col5 Col6 Col7
    •
    SOIL CLASS Df
    •
    TOTAL WALL HEIGHT = 10 FEET (INCLUDING STEM WALL AND BOND BEAM)
    •
    COB WALL HEIGHT PER TABLE BK106.11(1)
    •
    15 PSF ROOF-CEILING DEAD LOADd
    •
    STORY LOCATION: ONE-STORY BUILDING
    •
    SEISMIC DESIGN CATEGORY A
    •
    1.5″ PLASTER THICKNESS EACH SIDEg    		 •
    SOIL CLASS Df
    •
    TOTAL WALL HEIGHT = 10 FEET (INCLUDING STEM WALL AND BOND BEAM)
    •
    COB WALL HEIGHT PER TABLE BK106.11(1)
    •
    15 PSF ROOF-CEILING DEAD LOADd
    •
    STORY LOCATION: ONE-STORY BUILDING
    •
    SEISMIC DESIGN CATEGORY A
    •
    1.5″ PLASTER THICKNESS EACH SIDEg    		 •
    SOIL CLASS Df
    •
    TOTAL WALL HEIGHT = 10 FEET (INCLUDING STEM WALL AND BOND BEAM)
    •
    COB WALL HEIGHT PER TABLE BK106.11(1)
    •
    15 PSF ROOF-CEILING DEAD LOADd
    •
    STORY LOCATION: ONE-STORY BUILDING
    •
    SEISMIC DESIGN CATEGORY A
    •
    1.5″ PLASTER THICKNESS EACH SIDEg    		 •
    SOIL CLASS Df
    •
    TOTAL WALL HEIGHT = 10 FEET (INCLUDING STEM WALL AND BOND BEAM)
    •
    COB WALL HEIGHT PER TABLE BK106.11(1)
    •
    15 PSF ROOF-CEILING DEAD LOADd
    •
    STORY LOCATION: ONE-STORY BUILDING
    •
    SEISMIC DESIGN CATEGORY A
    •
    1.5″ PLASTER THICKNESS EACH SIDEg    		 MINIMUM TOTAL LENGTH (feet) OF COB BRACED WALL
    PANELS REQUIRED ALONG EACH BRACED WALL LINEa, b, c, d, e    		 MINIMUM TOTAL LENGTH (feet) OF COB BRACED WALL
    **PANELS REQUIRED ALONG EACH BRACED WALL LINEa, b, c, d,
  • CHBC § 1.5 High relevance — show source text

    2025 CALIFORNIA RESIDENTIAL CODE APPENDIX BK-15

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

    APPENDIX BK — COB CONSTRUCTION (MONOLITHIC ADOBE)

    TABLE BK106.11(5)—BRACING REQUIREMENTS FOR COB BRACED WALL PANELS BASED ON SEISMIC DESIGN CATEGORY C Col2 Col3 Col4 Col5 Col6 Col7
    •
    SOIL CLASS Df
    •
    TOTAL WALL HEIGHT = 10 FEET (INCLUDING STEM WALL AND BOND BEAM)
    •
    COB WALL HEIGHT PER TABLE BK106.11(1)
    •
    15 PSF ROOF-CEILING DEAD LOADd
    •
    STORY LOCATION: ONE-STORY BUILDING
    •
    SESIMIC DESIGN CATEGORY C
    •
    1.5″ PLASTER THICKNESS EACH SIDEg    		 •
    SOIL CLASS Df
    •
    TOTAL WALL HEIGHT = 10 FEET (INCLUDING STEM WALL AND BOND BEAM)
    •
    COB WALL HEIGHT PER TABLE BK106.11(1)
    •
    15 PSF ROOF-CEILING DEAD LOADd
    •
    STORY LOCATION: ONE-STORY BUILDING
    •
    SESIMIC DESIGN CATEGORY C
    •
    1.5″ PLASTER THICKNESS EACH SIDEg    		 •
    SOIL CLASS Df
    •
    TOTAL WALL HEIGHT = 10 FEET (INCLUDING STEM WALL AND BOND BEAM)
    •
    COB WALL HEIGHT PER TABLE BK106.11(1)
    •
    15 PSF ROOF-CEILING DEAD LOADd
    •
    STORY LOCATION: ONE-STORY BUILDING
    •
    SESIMIC DESIGN CATEGORY C
    •
    1.5″ PLASTER THICKNESS EACH SIDEg    		 •
    SOIL CLASS Df
    •
    TOTAL WALL HEIGHT = 10 FEET (INCLUDING STEM WALL AND BOND BEAM)
    •
    COB WALL HEIGHT PER TABLE BK106.11(1)
    •
    15 PSF ROOF-CEILING DEAD LOADd
    •
    STORY LOCATION: ONE-STORY BUILDING
    •
    SESIMIC DESIGN CATEGORY C
    •
    1.5″ PLASTER THICKNESS EACH SIDEg    		 MINIMUM TOTAL LENGTH (feet) OF COB BRACED WALL
    **PANELS REQUIRED ALONG EACH BRACED WALL LINEa, b, c, d,
  • CHBC § 1.5 High relevance — show source text

    APPENDIX BK-14 2025 CALIFORNIA RESIDENTIAL CODE

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

    APPENDIX BK — COB CONSTRUCTION (MONOLITHIC ADOBE)

    TABLE BK106.11(4)—BRACING REQUIREMENTS FOR COB BRACED WALL PANELS BASED ON SEISMIC DESIGN CATEGORY B—continued Col2 Col3 Col4 Col5 Col6 Col7
    •
    SOIL CLASS Df
    •
    TOTAL WALL HEIGHT = 10 FEET (INCLUDING STEM WALL AND BOND BEAM)
    •
    COB WALL HEIGHT PER TABLE BK106.11(1)
    •
    15 PSF ROOF-CEILING DEAD LOADd
    •
    STORY LOCATION: ONE-STORY BUILDING
    •
    SESIMIC DESIGN CATEGORY B
    •
    1.5″ PLASTER THICKNESS EACH SIDEg    		 •
    SOIL CLASS Df
    •
    TOTAL WALL HEIGHT = 10 FEET (INCLUDING STEM WALL AND BOND BEAM)
    •
    COB WALL HEIGHT PER TABLE BK106.11(1)
    •
    15 PSF ROOF-CEILING DEAD LOADd
    •
    STORY LOCATION: ONE-STORY BUILDING
    •
    SESIMIC DESIGN CATEGORY B
    •
    1.5″ PLASTER THICKNESS EACH SIDEg    		 •
    SOIL CLASS Df
    •
    TOTAL WALL HEIGHT = 10 FEET (INCLUDING STEM WALL AND BOND BEAM)
    •
    COB WALL HEIGHT PER TABLE BK106.11(1)
    •
    15 PSF ROOF-CEILING DEAD LOADd
    •
    STORY LOCATION: ONE-STORY BUILDING
    •
    SESIMIC DESIGN CATEGORY B
    •
    1.5″ PLASTER THICKNESS EACH SIDEg    		 •
    SOIL CLASS Df
    •
    TOTAL WALL HEIGHT = 10 FEET (INCLUDING STEM WALL AND BOND BEAM)
    •
    COB WALL HEIGHT PER TABLE BK106.11(1)
    •
    15 PSF ROOF-CEILING DEAD LOADd
    •
    STORY LOCATION: ONE-STORY BUILDING
    •
    SESIMIC DESIGN CATEGORY B
    •
    1.5″ PLASTER THICKNESS EACH SIDEg    		 MINIMUM TOTAL LENGTH (feet) OF COB BRACED WALL
    **PANELS REQUIRED ALONG EACH BRACED WALL LINEa, b, c, d,
  • CRC § 2500 High relevance — show source text

    4 bars****a
    •
    2 inches clear from bottom
    •
    2 inches clear from sides    a|CONCRETE:
    •
    2500 psi compressive strength
    •
    Height = 6 inches
    •
    Extend 1 foot beyond opening sides
    •
    Reinforcement two No. 4 bars    a
    •
    2 inches clear from bottom
    •
    2 inches clear from sides    a| |Building
    width (feet)|Cob above
    lintel (feet)|Total cob wall
    and plaster
    thickness
    (inches)|Size of wood lintel or bond beam—H ×W
    (nominal inches)    |Size of wood lintel or bond beam—H ×W
    (nominal inches)    |Width of concrete lintel or bond beam
    (inches)|Width of concrete lintel or bond beam
    (inches)| |Building
    width (feet)|Cob above
    lintel (feet)|Total cob wall
    and plaster
    thickness
    (inches)**|For span ≤ 4 ft|For span ≤ 6 ft|For span ≤ 6 ft|For span ≤ 8 ft| |10|0|≤ 27|4 × 8|4 × 8|8|8| |10|1|15|4 × 12|4 × 12|12|12| |10|1|19|4 × 16|4 × 16|16|16| |10|1|27|4 × 24|4 × 24|24|24| |10|2|15|4 × 12|6 × 12|12|12| |10|2|19|4 × 16|6 × 16|16|16| |10|2|27|4 × 24|4 × 24|24|24|

    2025 CALIFORNIA RESIDENTIAL CODE APPENDIX BK-11

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

    APPENDIX BK — COB CONSTRUCTION (MONOLITHIC ADOBE)

    TABLE BK106.10—LINTELS AND BOND BEAMS SPANNING OPENINGS—continued Col2 Col3 Col4 Col5 Col6 Col7
    GROUND SNOW LOAD ≤ 30 PSF GROUND SNOW LOAD ≤ 30 PSF GROUND SNOW LOAD ≤ 30 PSF WOOD:
    •
    _F_b ≥ 850 psi
    •
    E ≥ 1,300,000 psi
    •
    **No.
  • CHBC § 9.5. High relevance — show source text

    Attach rafters to bond beam with 4-inch by 3-inch by 3-inch by 18-gage tension tie angles at prescribed spacing. See Figure BK106.9.5. Where rafters are attached to tension
    ties, roof sheathing shall be edge nailed.
    g. All walls shall be tested for compressive strength in accordance with Section BK106.6.
    h. For curved walls with an arc length (ARCc) to radius (Rc) ratio of 1.5:1 or greater, the_H_/ T factor shall be increased by 1, and the absolute height limit by 1 foot. See Section
    BK106.11.3.
    i.
    Wall type requires a modulus of rupture test in accordance with Section BK106.7.
    j.
    See wall Type A in Table BK106.11(1) for top anchor requirements.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s.
    N/A = Not Applicable
    a. See Table BK106.11(1) for reinforcing and anchorage specifications for wall Types A, B, C, D and E.
    b._ H_ = height of the cob portion of the wall only. See Figure BK101.4. The maximum_H_ is the absolute limit or the limit based on wall thickness, whichever is more restrictive.
    c. Bond beams or other horizontal restraints are permitted to divide a wall into more than one unrestrained wall height with an approved engineered design.
    d._ T_= Cob wall thickness (in feet) at its minimum, without plaster.
    e.
    5/8-inch threaded rod anchors at prescribed spacing with 12-inch embedment in cob, full embedment in concrete bond beams or full penetration in wood bond beam with a
    nut and washer.
    f. Attach rafters to bond beam with 4-inch by 3-inch by 3-inch by 18-gage tension tie angles at prescribed spacing. See Figure BK106.9.5. Where rafters are attached to tension
    ties, roof sheathing shall be edge nailed.
    g. All walls shall be tested for compressive strength in accordance with Section BK106.6.
    h. For curved walls with an arc length (ARCc) to radius (Rc) ratio of 1.5:1 or greater, the_H_/ T factor shall be increased by 1, and the absolute height limit by 1 foot. See Section
    BK106.11.3.
    i.
    Wall type requires a modulus of rupture test in accordance with Section BK106.7.
    j.
    See wall Type A in Table BK106.11(1) for top anchor requirements.|

    APPENDIX BK-6 2025 CALIFORNIA RESIDENTIAL CODE

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

    APPENDIX BK — COB CONSTRUCTION (MONOLITHIC ADOBE)

Frequently asked questions

Can I use the numeric bond‑beam sizes from the regular CBC to comply with § 8-806.5?

The CHBC § 8-806.5 does not prescribe numeric bond‑beam sizes — it requires the element be “sufficient” to brace the wall and tie to floor/roof. Use a registered design professional to size details or obtain enforcing‑agency concurrence.

How exactly do I measure the wall “height” for the ratio?

Measure floor‑to‑floor height for stories (the CHBC explicitly says the two‑story ratios are measured at floor‑to‑floor height) and the usual wall‑clear vertical distance for one‑story walls. § 8-806.3

Do nonload‑bearing adobe partitions have numeric H:T limits in the CHBC?

No numeric H:T limit is provided for nonload‑bearing partitions; § 8-806.4 requires evaluation for stability and anchorage against out‑of‑plane failure if necessary.

What if my existing historic wall exceeds the CHBC ratio limits?

The CHBC anticipates that existing walls may not meet the ratios and states additional strengthening measures (such as a bond beam) may be appropriate; the chosen retrofit and its design should be by an RDP and coordinated with the enforcing agency. § 8-806.3 and § 8-806.5.

Does the CHBC address moisture or material compatibility for adobe repairs?

Yes — § 8-806.2 requires moisture‑protection measures and attention to adobe condition; repairs and mortar compatibility are addressed elsewhere in the adobe section.

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