CHBC · California Historical Building Code

What are CHBC rules for repair/reconstruction, shear values and mortar compatibility for adobe?

For homeowners: CHBC allows in-kind repairs of historic adobe using unstabilized adobe and soil-based mortar that match the original; engineers usually assume a conservative shear strength of 12 psi for existing adobe unless testing justifies a different value, and full rebuilds may require meeting current code.

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

Repairs and limited reconstructions of adobe in a qualified historical building may be done in-kind using unstabilized adobe or brick that is designed to be compatible with the constituents of the existing adobe (§ 8-806.6) . The CHBC allows existing adobe to be assigned a maximum shear strength of 12 pounds per square inch (82.7 kPa) (§ 8-806.7) . Mortar may be of the same soil composition as the existing wall—or otherwise selected to be compatible with the adobe units (§ 8-806.8) .

Repairs to adobe should be in-kind and compatible with the original materials; for structural evaluation, existing adobe is typically capped at 12 psi shear unless testing and agency concurrence support otherwise.

Key controlling sections (first mention bolded)

  • § 8-806.6 — Repair or reconstruction
  • § 8-806.7 — Shear values (12 psi / 82.7 kPa)
  • § 8-806.8 — Mortar compatibility (same soil composition allowed)

Requirements in detail

1) Repair / Reconstruction (what you are allowed to do)

  • Allowed: Repairs or reconstruction of wall area may use unstabilized brick or adobe masonry so long as the repair material is designed to be compatible with the constituents of the existing adobe (§ 8-806.6) .
  • Note: A totally reconstructed wall using original brick or masonry that is rebuilt similar to the original may be required to be built to the regular (non‑historical) code; partial repairs/infill may be done in a similar manner to the original without conforming to the regular code (see § 8-805.3) .
  • Practical implication: small-to-moderate in-kind repairs (matching soil, size, compaction/stabilization) are explicitly allowed; full re-builds may trigger regular code requirements.

2) Shear values (what strength you can assume)

  • The CHBC explicitly states existing adobe may be allowed a maximum shear strength of 12 psi (82.7 kPa) (§ 8-806.7) .
  • Who assigns values: the CHBC also requires the architect/engineer in responsible charge to investigate and assign allowable stresses (and values shall not exceed those provided without testing) — see § 8-802 (general engineering approach) .
  • If higher values are desired, they must be justified by testing and the approval process described by the CHBC and the enforcing agency (see §§ 8-802 and 8-804) .

3) Mortar compatibility (what mortar you may use)

  • CHBC permits mortar to be of the same soil composition as that used in the existing wall, or in new walls to be compatible with the adobe brick (§ 8-806.8) .
  • Practical guidance: this means soil-based (earth) mortars that match the brick are explicitly allowed. The code therefore recognizes that cement‑rich mortars can be incompatible and that matching composition is an approved solution; selection should still be confirmed by the project engineer/architect and the enforcing agency.

Decision-relevant table

Decision item Requirement / value Code Reference
Repair method allowed Use of unstabilized brick/adobe masonry when compatible with existing constituents § 8-806.6
Maximum shear to assume for existing adobe 12 psi (82.7 kPa) (existing adobe may be allowed this maximum strength level) § 8-806.7
Mortar for repointing or new small repairs Mortar may be of the same soil composition or otherwise compatible with adobe brick § 8-806.8
Totally reconstructed walls Full reconstructions using original masonry may have to comply with the regular code; repairs/infill may be in-kind § 8-805.3
Who assigns allowable stresses Architect/engineer must assign allowable stresses; values shall not exceed CHBC provisions without testing and agency concurrence § 8-802

Exceptions & special cases

  • Total replacement: If a wall is totally reconstructed (even using original bricks), the CHBC says it “shall be constructed in accordance with the regular code”; partial repairs or infill can remain in-kind under CHBC § 8-805.3 .
  • Higher shear values: The CHBC caps existing adobe at 12 psi for design unless testing and a responsible design professional justify a higher value; the engineer’s assigned values are subject to the enforcing agency’s concurrence (§ 8-806.7, § 8-802) .
  • Mortar: While soil‑based mortar is allowed and often preferred for compatibility, any mortar used should be shown to be compatible with the adobe units — testing or professional judgment may be needed where composition differs (§ 8-806.8) .

Common mistakes

  • Assuming you can always rebuild to the CHBC in-kind: a full rebuild may require compliance with the regular (current) code — check § 8-805.3 .
  • Using Portland-cement rich mortar without evaluation: cement mortar is often much harder and less permeable than earthen adobe; CHBC explicitly allows soil‑composition mortar to preserve compatibility (§ 8-806.8) .
  • Treating the 12 psi shear as a universal “capacity” for every detail: 12 psi is the CHBC maximum for existing adobe per § 8-806.7, but the project’s structural survey and engineer may assign different allowable stresses after testing or based on wall geometry (see § 8-802) .
  • Forgetting enforcing‑agency concurrence: CHBC frequently requires the enforcing agency’s concurrence for alternative approaches and assigned values — don’t skip that step (see § 8-801.1 and § 8-802) .

Worked example — applying the rule with numbers

Scenario: You are repairing a single stretch of existing adobe wall and want to estimate the shear resistance along its base for preliminary checks.

Given:

  • Wall segment length = 8 ft (96 in)
  • Wall thickness = 12 in (1 ft) — many exterior adobe walls are ~10–14 in; use actual measured thickness in practice
  • CHBC maximum allowable shear stress for existing adobe = 12 psi (82.7 kPa) per § 8-806.7

Calculation:

  • Shear resisting area (base plane) = thickness × length = 12 in × 96 in = 1,152 in²
  • Allowable shear force = shear stress × area = 12 psi × 1,152 in² = 13,824 lb (≈ 6.9 tons)

Interpretation:

  • Under CHBC default allowance you could preliminarily assume this wall segment could resist up to ~13,800 lb of shear along that base plane, using the CHBC maximum shear stress.
  • Important caveats: this is a simplified calculation. The architect/engineer must perform a full structural survey, consider load path, connections, out‑of‑plane stability, axial loads, and obtain enforcing‑agency concurrence. The CHBC also requires the design professional to assign allowable stresses (see § 8-802) .

Related provisions (CHBC sections)

  • § 8-806.1 — General (scope and agency concurrence for alternatives)
  • § 8-806.2 — Moisture protection; protect adobe from moisture deterioration
  • § 8-806.3 — Height‑to‑thickness ratios for out‑of‑plane evaluation of adobe walls
  • § 8-806.5 — Bond beam guidance for adobe walls (top/top of second floor)
  • § 8-805.3 — Reconstructed walls: total reconstruction vs. repair/infill (regular code vs. CHBC)
  • § 8-802 — General engineering approaches; assign stresses and testing requirements (architect/engineer responsibility)
  • § 8-703 — Structural survey requirement (documents existing conditions relevant to allowable stresses)

(If you need the exact text of any of these sections I referenced, I can pull the section language and show the precise lines with citations.)

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 § 8-806.4 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 § 7-3 High relevance — show source text

    702 Building Elements and Materials . . . . . . . . . . . . . . . . . 7-3

    703 Fire Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

    704 Means of Egress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

    705 Reroofing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

    706 Structural. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5

    707 Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

    708 Energy Conservation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

    CHAPTER 8 ALTERATIONS—LEVEL 2 . . . . . . . . . . . . . . . . . .8-3

    801 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

    802 Building Elements and Materials . . . . . . . . . . . . . . . . . 8-3

    803 Fire Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-5

    804 Means of Egress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-5

    805 Structural. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9

    806 Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-10

    807 Mechanical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-10

    808 Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-10

    809 Energy Conservation. . . . . . . . . . . . . . . . . . . . . . . . . . . 8-10

    CHAPTER 9 ALTERATIONS—LEVEL 3 . . . . . . . . . . . . . . . . . .9-3

    901 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3

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

    CHAPTER 8-8 ARCHAIC MATERIALS AND METHODS OF

    CONSTRUCTION . . . . . . . . . . . . . . . . . . . . . . . 15

    Section

    8-801 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 15 8-802 General Engineering Approaches. . . . . . . . . . . . . . . . . 15 8-803 Nonstructural Archaic Materials. . . . . . . . . . . . . . . . . . 15

    8-804 Allowable Conditions for Specific Materials . . . . . . . 15 8-805 Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 8-806 Adobe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

    8-807 Wood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

    8-808 Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

    8-809 Steel and Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

    8-810 Hollow Clay Tile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

    8-811 Veneers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

    8-812 Glass and Glazing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

    CHAPTER 8-9 MECHANICAL, PLUMBING AND ELECTRICAL REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . 19

    Section

    8-901 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 19 8-902 Mechanical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

    8-903 Plumbing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 8-904 Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

    CHAPTER 8-10 QUALIFIED HISTORICAL DISTRICTS,

    SITES AND OPEN SPACES . . . . . . . . . . . . . . . 23

    Section

  • CHBC § 8-1 High relevance — show source text

    CHAPTER 8 INTERIOR FINISHES. . . . . . . . . . . . . . . . . . . . . .8-1

    801 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

    802 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

    803 Wall and Ceiling Finishes . . . . . . . . . . . . . . . . . . . . . . . . 8-3

    804 Interior Floor Finish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6

    805 Combustible Materials in Types I and II Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-7

    806 Decorative Materials and Trim . . . . . . . . . . . . . . . . . . . 8-7

    807 Insulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-8

    808 Acoustical Ceiling Systems . . . . . . . . . . . . . . . . . . . . . . 8-8

    CHAPTER 9 FIRE PROTECTION AND LIFE

    SAFETY SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-1

    901 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7

    902 Fire Pump and Riser Room Size . . . . . . . . . . . . . . . . . . 9-7

    903 Automatic Sprinkler Systems . . . . . . . . . . . . . . . . . . . . 9-8

    904 Alternative Automatic Fire-Extinguishing Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-17

    905 Standpipe Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-20

    906 Portable Fire Extinguishers . . . . . . . . . . . . . . . . . . . . . 9-22

    907 Fire Alarm and Detection Systems . . . . . . . . . . . . . . . 9-25

    908 Emergency Alarm Systems . . . . . . . . . . . . . . . . . . . . . 9-43

    909 Smoke Control Systems . . . . . . . . . . . . . . . . . . . . . . . . 9-43

    910 Smoke and Heat Removal . . . . . . . . . . . . . . . . . . . . . . 9-51

  • CHBC § 8-6 Medium relevance — show source text

    CHAPTER 8-6 ACCESSIBILITY . . . . . . . . . . . . . . . . . . . . . . . . 11

    Section

    8-601 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 11

    8-602 Basic Provisions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

    8-603 Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

    8-604 Equivalent Facilitation. . . . . . . . . . . . . . . . . . . . . . . . . . 12

    CHAPTER 8-7 STRUCTURAL REGULATIONS. . . . . . . . . . . . . 13

    Section

    8-701 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 13 8-702 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

    8-703 Structural Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8-704 Nonhistorical Additions and

    Nonhistorical Alterations . . . . . . . . . . . . . . . . . . . . . . . 13

    8-705 Structural Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8-706 Lateral Load Regulations. . . . . . . . . . . . . . . . . . . . . . . . 14

    CHAPTER 8-8 ARCHAIC MATERIALS AND METHODS OF

    CONSTRUCTION . . . . . . . . . . . . . . . . . . . . . . . 15

    Section

    8-801 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 15 8-802 General Engineering Approaches. . . . . . . . . . . . . . . . . 15 8-803 Nonstructural Archaic Materials. . . . . . . . . . . . . . . . . . 15

    8-804 Allowable Conditions for Specific Materials . . . . . . . 15 8-805 Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 8-806 Adobe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

    8-807 Wood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

    8-808 Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

  • CHBC § 8-804 Medium relevance — show source text

    SECTION 8-804 — ALLOWABLE CONDITIONS FOR SPECIFIC MATERIALS

    Archaic materials which exist and are to remain in qualified historical buildings or structures shall be evaluated for their condition and for loads required by this code. The structural survey required in Section 8-703 of the CHBC shall document existing conditions, reinforcement, anchorage, deterioration and other factors pertinent to establishing allowable stresses, strength levels and adequacy of the archaic materials. The remaining portion of this chapter provides additional specific requirements for commonly encountered archaic materials.

    SECTION 8-805 — MASONRY

    For adobe, see Section 8-806.

    8-805.1 Existing solid masonry. Existing solid masonry walls of any type, except adobe, may be allowed, without testing, a maximum ultimate strength of 9 pounds per square inch (62.1 kPa) in shear where there is a qualifying statement by the architect or engineer that an inspection has been made, that mortar joints are filled and that both brick and mortar are reasonably good. The shear stress above applies to unreinforced masonry, except adobe, where the maximum ratio of unsupported height or length to thickness does not exceed 13, and where minimum quality mortar is used or exists. Wall height or length is measured to supporting or resisting elements that are at least twice as stiff as the tributary wall. Stiffness is based on the gross section. Shear stress may be increased by the addition of 10 percent of the axial direct stress due to the weight of the wall directly above. Higher-quality mortar may provide a greater shear value and shall be tested in accordance with Appendix A, Chapter A1 of the California Existing Building Code (CEBC) 2010 edition, and as modified by the CHBC.

    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.

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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.

  • CHBC § 0.3 Medium 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

    2025 CALIFORNIA EXISTING BUILDING CODE APPENDIX A-17

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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

  • CHBC § 62.1 Medium relevance — show source text
    1. 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.
    2. 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

    2025 CALIFORNIA EXISTING BUILDING CODE APPENDIX A-17

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

    APPENDIX A-18 2025 CALIFORNIA EXISTING BUILDING CODE

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

    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

    (Matrix Adoption Tables are nonregulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

    Adopting Agency BSC BSC-
    CG    		 SFM HCD Col6 Col7 DSA Col9 Col10 OSHPD Col12 Col13 Col14 Col15 Col16 Col17 BSCC DPH AGR DWR CEC CA SL SLC
    Adopting Agency BSC BSC-
    CG    		 SFM 1 2 1/AC AC SS SS/CC 1 1R 2 3 4 5 6 6 6 6 6 6 6 6 6
    Adopt Entire Chapter
    Adopt Entire Chapter as
    amended (amended
    sections listed below)    		 X
    Adopt only those sections
    that are listed below
    Chapter / Section
    A202.1 X

    The state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.

  • CHBC § 8-801 Medium relevance — show source text

    SECTION 8-801 — PURPOSE, INTENT AND SCOPE

    8-801.1 Purpose. The purpose of the CHBC is to provide regulations for the use of historical methods and materials of construction that are at variance with regular code requirements or are not otherwise codified, in buildings or structures designated as qualified historical buildings or properties. The CHBC require enforcing agencies to accept any reasonably equivalent alternatives to the regular code when dealing with qualified historical buildings or properties.

    8-801.2 Intent. It is the intent of the CHBC to provide for the use of historical methods and materials of construction that are at variance with specific code requirements or are not otherwise codified.

    8-801.3 Scope. Any construction type or material that is, or was, part of the historical fabric of a structure is covered by this chapter. Archaic materials and methods of construction present in a historical structure may remain or be reinstalled or be installed with new materials of the same class to match existing conditions.

    SECTION 8-802 — GENERAL ENGINEERING APPROACHES

    Strength values for archaic materials shall be assigned based upon similar conventional codified materials, or on tests as hereinafter indicated. The archaic materials and methods of construction shall be thoroughly investigated for their details of construction in accordance with Section 8-703. Testing shall be performed when applicable to evaluate existing conditions. The architect or structural engineer in responsible charge of the project shall assign allowable stresses or strength levels to archaic materials. Such assigned strength values shall not be greater than those provided for in the following sections without adequate testing, and shall be subject to the concurrence of the enforcing agency.

    SECTION 8-803 — NONSTRUCTURAL ARCHAIC MATERIALS

    Where nonstructural historical materials exist in uses which do not meet the requirements of the regular code, their continued use is allowed by this code, provided that any public health and life safety hazards are mitigated subject to the concurrence of the enforcing agency.

    SECTION 8-804 — ALLOWABLE CONDITIONS FOR SPECIFIC MATERIALS

    Archaic materials which exist and are to remain in qualified historical buildings or structures shall be evaluated for their condition and for loads required by this code. The structural survey required in Section 8-703 of the CHBC shall document existing conditions, reinforcement, anchorage, deterioration and other factors pertinent to establishing allowable stresses, strength levels and adequacy of the archaic materials. The remaining portion of this chapter provides additional specific requirements for commonly encountered archaic materials.

    SECTION 8-805 — MASONRY

    For adobe, see Section 8-806.

    8-805.1 Existing solid masonry. Existing solid masonry walls of any type, except adobe, may be allowed, without testing, a maximum ultimate strength of 9 pounds per square inch (62.1 kPa) in shear where there is a qualifying statement by the architect or engineer that an inspection has been made, that mortar joints are filled and that both brick and mortar are reasonably good. The shear stress above applies to unreinforced masonry, except adobe, where the maximum ratio of unsupported height or length to thickness does not exceed 13, and where minimum quality mortar is used or exists. Wall height or length is measured to supporting or resisting elements that are at least twice as stiff as the tributary wall. Stiffness is based on the gross section. Shear stress may be increased by the addition of 10 percent of the axial direct stress due to the weight of the wall directly above.

  • CHBC § 2109.2.3.1 Medium relevance — show source text
    TABLE 2109.2.3.1—ALLOWABLE SHEAR ON BOLTS IN ADOBE MASONRY Col2 Col3
    DIAMETER OF BOLTS (inches) MINIMUM EMBEDMENT (inches) SHEAR (pounds)
    1/2 — —
    5/8 12 200
    3/4 15 300
    7/8 18 400
    1 21 500
    11/8 24 600
    For SI: 1 inch = 25.4 mm, 1 pound = 4.448 N. For SI: 1 inch = 25.4 mm, 1 pound = 4.448 N. For SI: 1 inch = 25.4 mm, 1 pound = 4.448 N.

    2109.2.4 Detailed requirements. Adobe construction shall comply with Sections 2109.2.4.1 through 2109.2.4.9.

    2109.2.4.1 Number of stories. Adobe construction shall be limited to buildings not exceeding one story, except that two-story construction is allowed where designed by a registered design professional.

    2025 CALIFORNIA BUILDING CODE 21-9

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    MASONRY

    2109.2.4.2 Mortar. Mortar for adobe construction shall comply with Sections 2109.2.4.2.1 and 2109.2.4.2.2.

    2109.2.4.2.1 General. Mortar for adobe units shall be in accordance with Section 2103.2.1, or be composed of adobe soil of the same composition and stabilization as the adobe brick units. Unstabilized adobe soil mortar is permitted in conjunction with unstabilized adobe brick units.

    2109.2.4.2.2 Mortar joints. Adobe units shall be laid with full head and bed joints and in full running bond.

    2109.2.4.3 Parapet walls. Parapet walls constructed of adobe units shall be waterproofed.

    2109.2.4.4 Wall thickness. The minimum thickness of exterior walls in one-story buildings shall be 10 inches (254 mm). The walls shall be laterally supported at intervals not exceeding 24 feet (7315 mm). The minimum thickness of interior load-bearing walls shall be 8 inches (203 mm). The unsupported height of any wall constructed of adobe units shall not exceed 10 times the thickness of such wall.

    2109.2.4.5 Foundations. Foundations for adobe construction shall be in accordance with Sections 2109.2.4.5.1 and

    2109.2.4.5.2.

    2109.2.4.5.1 Foundation support. Walls and partitions constructed of adobe units shall be supported by foundations or footings that extend not less than 6 inches (152 mm) above adjacent ground surfaces and are constructed of solid masonry (excluding adobe) or concrete. Footings and foundations shall comply with Chapter 18.

    2109.2.4.5.2 Lower course requirements. Stabilized adobe units shall be used in adobe walls for the first 4 inches (102 mm) above the finished first-floor elevation.

  • CHBC § 2109.2.1.3 Medium relevance — show source text

    2109.2.1.3 Moisture content requirements. Adobe units shall have a moisture content not exceeding 4 percent by weight.

    2109.2.1.4 Shrinkage cracks. Adobe units shall not contain more than three shrinkage cracks and any single shrinkage crack shall not exceed 3 inches (76 mm) in length or [1] / 8 inch (3.2 mm) in width.

    2109.2.2 Stabilized adobe. Stabilized adobe shall comply with Section 2109.2.1 for unstabilized adobe in addition to Sections 2109.2.2.1 and 2109.2.2.2.

    2109.2.2.1 Soil requirements. Soil used for stabilized adobe units shall be chemically compatible with the stabilizing material.

    2109.2.2.2 Absorption requirements. A 4-inch (102 mm) cube, cut from a stabilized adobe unit dried to a constant weight in a ventilated oven at 212°F to 239°F (100°C to 115°C), shall not absorb more than 2 [1] / 2 percent moisture by weight when placed on a constantly water-saturated, porous surface for seven days. Not fewer than five specimens shall be tested and each specimen shall be cut from a separate unit.

    2109.2.3 Allowable stress. The allowable compressive stress based on gross cross-sectional area of adobe shall not exceed 30 psi (207 kPa).

    2109.2.3.1 Bolts. Bolt values shall not exceed those set forth in Table 2109.2.3.1.

    TABLE 2109.2.3.1—ALLOWABLE SHEAR ON BOLTS IN ADOBE MASONRY Col2 Col3
    DIAMETER OF BOLTS (inches) MINIMUM EMBEDMENT (inches) SHEAR (pounds)
    1/2 — —
    5/8 12 200
    3/4 15 300
    7/8 18 400
    1 21 500
    11/8 24 600
    For SI: 1 inch = 25.4 mm, 1 pound = 4.448 N. For SI: 1 inch = 25.4 mm, 1 pound = 4.448 N. For SI: 1 inch = 25.4 mm, 1 pound = 4.448 N.

    2109.2.4 Detailed requirements. Adobe construction shall comply with Sections 2109.2.4.1 through 2109.2.4.9.

    2109.2.4.1 Number of stories. Adobe construction shall be limited to buildings not exceeding one story, except that two-story construction is allowed where designed by a registered design professional.

    2025 CALIFORNIA BUILDING CODE 21-9

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

    MASONRY

    2109.2.4.2 Mortar. Mortar for adobe construction shall comply with Sections 2109.2.4.2.1 and 2109.2.4.2.2.

Frequently asked questions

Can I use modern cement mortar to repoint an old adobe wall?

The CHBC explicitly allows mortar that is of the same soil composition as the existing wall or mortar that is compatible with the adobe brick (§ 8-806.8) . Cement‑rich mortar is often incompatible; use of cement mortar should be justified by an engineer and approved by the enforcing agency.

Is 12 psi a guaranteed capacity for all adobe walls?

No. § 8-806.7 states existing adobe may be allowed a maximum of 12 psi for shear, but the architect/engineer must assign allowable stresses after inspection and testing and values over the CHBC default require justification and agency concurrence (§ 8-802) .

If I completely rebuild an adobe wall using the same bricks, can I use CHBC rules?

Totally reconstructed walls using original brick and constructed similar to the original shall be constructed in accordance with the regular code; repairs/infill can be done in-kind under CHBC (§ 8-805.3) .

Who decides whether a proposed in-kind repair is acceptable?

The project’s architect or structural engineer assigns allowable stresses and documents conditions; the enforcing agency must concur with alternatives and assigned values per CHBC procedures (see § 8-802 and § 8-801.1) .

If I want to assume a higher shear value than 12 psi, what must I do?

You need representative testing or other engineering justification and the architect/engineer must document and assign the higher value; the enforcing agency must concur (see § 8-802 and related sections) .

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