CHBC · California Historical Building Code

How must unreinforced masonry buildings be evaluated and improved seismically?

If your historic building has unreinforced masonry bearing walls, the CHBC requires evaluation and seismic repairs using the CEBC Appendix A1 procedures (adopted by **§ 8‑706.1.2**). A qualified architect/engineer must survey and test the masonry (mortar shear and tensile tests, lay‑up inspection). If masonry fails CEBC minimums (for example lower‑bound mortar shear < **30 psi** or unsupported height/thickness > **13**), the CHBC directs repointing, retesting, anchorage, or replacement to achieve a continuous load path and meet the CHBC performance objectives.

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Last reviewed: July 6, 2026

What the code requires — in plain English

The California Historical Building Code requires that evaluation and seismic improvement of unreinforced masonry (URM) bearing‑wall buildings follow the procedures in the California Existing Building Code (CEBC), Appendix Chapter A1 (2013 edition) as modified by the CHBC — i.e., you use the CEBC Appendix A1 test/classification/retrofit procedures unless a CHBC modification or approved alternative applies. See § 8-706.1.2.

The single controlling rule: URM bearing‑wall buildings must be evaluated and retrofitted using the CEBC Appendix A1 procedures adopted by the CHBC (with CHBC exceptions and modifications). § 8-706.1.2

Requirements in detail

High‑level required steps (how the CHBC directs you to proceed)

  • Perform a documented structural survey by an architect or structural engineer experienced with historic structures (see § 8-703.1).
  • Evaluate existing URM walls using the CEBC Appendix A1 tests and classification procedures (in‑place shear, splitting tensile, lay‑up inspection, mortar condition, etc.), as adopted by the CHBC via § 8-706.1.2.
  • Where masonry does not meet CEBC minimums, repair (repointing), reinforce, replace, or provide new structural elements and anchorage so the building meets CHBC performance objectives (prevent collapse / reduce life‑threatening failure) per § 8-701.2 and § 8-705.2.1.

Key decision‑relevant dimensions, thresholds and test values

Decision / dimension Critical value or rule Code reference
Governing requirement for URM evaluation/retrofit Use CEBC Appendix Chapter A1 (2013) as modified by CHBC § 8-706.1.2
Allowable ultimate shear (without testing) for existing solid masonry (non‑adobe) 9 psi ultimate shear (when inspection confirms filled joints and reasonably good brick & mortar; applies where unsupported height/length : thickness ≤ 13) § 8-805.1
Maximum unsupported height/length : thickness ratio for the above allowance 13 § 8-805.1
Minimum mortar shear strength triggering pointing/retest lower bound (mean − 1σ) < 30 psi → must point & retest or replace/anchor CEBC § A106.2.3.6 (adopted/used per § 8-706.1.2)
Minimum average splitting tensile (fsp) mean ≥ 50 psi; lower values → pointing & retest CEBC § A106.2.3.7
Lay‑up / composite requirement for multiple‑wythe walls (headers) Not less than 10% of exposed face area in headers extending ≥ 4 in into backing; header spacing ≤ 24 in CEBC § A106.2.2.1 (applies via § 8-706.1.2)
When new lateral system R‑value may be used New system may be used if it resists ≥ 75% of base shear § 8-706.1.1
Limitation on seismic forces used under CHBC Forces need not exceed 0.75 × the regular code seismic forces; base shear caps of 0.30 W (Risk Cat I/II) and 0.40 W (Risk Cat III/IV) also apply § 8-706.1 (exceptions)
Tension / shear bolt typical capacities (design reference values) e.g., 5,400 lb per embedded through‑bolt in 3‑wythe wall (varies by detail); shear bolt capacities given by bolt size (½″ = 1,050 lb, ⅝″ = 1,500 lb, ¾″ = 2,250 lb) CHBC Appendix values (see CHBC table) — apply via § 8-706.1.2 and CHBC modification notes

Practical elements that must be checked and/or provided

  • Confirm masonry lay‑up (running bond / adequate headers) and collar joints; if wythes act as veneer they are not counted in effective thickness for stability calculations (CEBC rules adopted per § 8-706.1.2).
  • Perform in‑place mortar shear tests (ASTM C1531) and splitting tensile tests as required by CEBC Appendix A1; use statistical interpretation (mean and standard deviation) to classify walls and decide on pointing/retesting or replacement. (CEBC test procedures adopted; CHBC directs use of CEBC Appendix A1.)
  • Provide anchorage (through‑bolts, embedded rods, anchors at floor/roof lines) or new lateral resistance when masonry strength, detailing, or wall slenderness cannot meet the performance objective without intervention — see CHBC requirement for a continuous load path and ties § 8-706.3 and survey requirements § 8-703.

Exceptions & special cases

  • The CHBC permits case‑by‑case use of alternative standards if approved by the authority having jurisdiction (AHJ); such alternatives may supersede CEBC A1 when documented and approved (CHBC § 8-706.1.2 exceptions).
  • The CHBC allows exceeding the 100 psi strength limitation in CEBC A108.2 where test data and building configuration justify it and the AHJ approves. (This is a CHBC exception to the CEBC numeric limit.) § 8-706.1.2 (Exception 1).
  • CEBC Section A102.2 (some CEBC procedural provisions) is not applied to Qualified Historical Buildings in Risk Category III and certain public‑assembly occupancies per CHBC Exception 2 to § 8-706.1.2.
  • CHBC allows reduced seismic force levels relative to the regular code (e.g., ≤ 0.75× regular code forces) for strength‑level evaluation § 8-706.1; use these caps where applicable.

Common mistakes

  • Treating CHBC as identical to the regular CBC: CHBC requires CEBC Appendix A1 procedures for URM evaluation but also includes CHBC‑specific exceptions and allowable relaxed force levels — cite § 8-706.1.2 and § 8-706.1.
  • Skipping the structural survey by a qualified architect/engineer: CHBC § 8-703.1 mandates a documented survey addressing deterioration, detailing, reinforcement and anchorage before design.
  • Relying on small, non‑representative test samples: CEBC/CHBC require statistically appropriate sampling and reporting (mean and standard deviation) to establish lower bound strengths (see CEBC A106.2.3 procedures adopted by CHBC § 8-706.1.2).
  • Ignoring composite behavior: failing to verify header bonding and collar joints can lead to over‑estimating effective thickness; CEBC lay‑up rules govern whether wythes count toward thickness.
  • Assuming parapets or veneers are exempt: CHBC separately requires evaluation/anchorage of parapets and nonstructural features (see § 8-706.4 and § 8-706.5).

Worked example — a concrete scenario

Scenario: A 2‑story historic commercial building has unreinforced solid brick bearing walls, 20 ft unsupported wall height to the next diaphragm, and wall thickness 12 in. The owner wants to know whether pointing and anchors are required.

Step 1 — check height‑to‑thickness ratio:

  • Unsupported height / thickness = 20 ft / 1 ft = 20. The CHBC allowance for treating masonry as having the 9 psi ultimate shear without testing applies only where ratio ≤ 13 per § 8-805.1. Here 20 > 13, so the “no‑test 9 psi” allowance does not apply; testing and/or strengthening are needed.

Step 2 — perform in‑place mortar shear tests and splitting tensile tests per CEBC Appendix A1 (adopted per § 8-706.1.2). Suppose the tests give:

  • Mean mortar shear = 35 psi, standard deviation = 6 psi → lower bound = 35 − 6 = 29 psi.
  • Mean splitting fsp = 55 psi, σ = 7 → lower bound = 48 psi.

Step 3 — interpret results against CEBC minima:

  • Lower bound mortar shear 29 psi < 30 psi → CEBC § A106.2.3.6 requires pointing and retest or replacement/anchorage (applies via CHBC § 8-706.1.2). So the engineer must specify repointing and re‑testing.
  • Splitting tensile lower bound 48 psi < 50 psi → also indicates pointing and retest per CEBC § A106.2.3.7.

Step 4 — if re‑testing after pointing still shows inadequate strength, the retrofit options (per CEBC procedures) include:

  • Install through‑bolts or embedded anchors at floor/roof lines and provide a continuous load path to the foundation (CHBC § 8-706.3, and CEBC anchorage provisions adopted by CHBC).
  • Provide new lateral system elements (frames, shear walls) sized so the new system resists ≥ 75% of base shear if using the new system’s R‑value (CHBC § 8-706.1.1).

Result (practical): At minimum, the owner should expect repointing and retesting; probable anchorage (wall anchors/through‑bolts at diaphragm lines) or replacement of deficient wall sections if the re‑test does not meet CEBC minimums per CHBC direction.

Related provisions (CHBC)

  • § 8-706.1 — Seismic forces for CHBC evaluations (force limits and caps).
  • § 8-706.1.1 — Use of R‑value for new lateral systems when they resist ≥ 75% of base shear.
  • § 8-706.3 — Required continuous load path and ties between elements.
  • § 8-706.4 — Parapet investigation and anchorage.
  • § 8-706.5 — Nonstructural features (veneers, cornices) to be evaluated/anchored.
  • § 8-703.1 — Structural survey scope (must be done by an architect or engineer familiar with historic structures).
  • § 8-805.1 — CHBC allowable conditions for existing solid masonry (9 psi allowance; height/thickness ratio ≤ 13).
  • CEBC Appendix A (e.g., § A106.2.3.6, § A106.2.3.7, § A106.2.2.1) — testing, mortar thresholds, lay‑up and header rules as applied by CHBC § 8-706.1.2.

Code references

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

  • CHBC § 8-706 High relevance — show source text

    SECTION 8-706 — LATERAL LOAD REGULATIONS

    8-706.1 Seismic forces. Strength-level seismic forces used to evaluate the structure for resistance to seismic loads shall be based on the R -values tabulated in the regular code for similar lateral-force-resisting systems including consideration of the structural detailing of the members where such R -values exist. Where such R -values do not exist, an appropriate R -value shall be rationally assigned considering the structural detailing of the members.

    Exceptions:

    1. The forces need not exceed 0.75 times the seismic forces prescribed by the regular code requirements.
    2. For Risk Category I, II or III structures, near-fault increases in ground motion (maximum considered earthquake ground motion of 0.2 second spectral response greater than 150 percent at 5 percent damping) need not be considered when the fundamental period of the building is 0.5 seconds in the direction under consideration.
    3. For Risk Category I or II structures, the seismic base shear need not exceed 0.30W.
    4. For Risk Category III or IV structures, the seismic base shear need not exceed 0.40W.

    8-706.1.1 When a building is to be strengthened with the addition of a new lateral force resisting system, the R -value of the new system can be used when the new lateral force resisting system resists at least 75 percent of the building’s base shear regardless of its relative rigidity.

    8-706.1.2 Evaluation and seismic improvement of unreinforced masonry bearing wall buildings shall comply with the California Existing Building Code (CEBC), Appendix Chapter A1 2013 Edition, and as modified by the CHBC.

    Exceptions:

    1. Alternative standards may be used on a case-by-case basis when approved by the authority having jurisdiction. It shall be permitted to exceed the strength limitation of 100 psi in Section A108.2 of the CEBC when test data and building configuration supports higher values subject to the approval of the authority having jurisdiction.
    2. CEBC Section A102.2 shall not apply to Qualified Historical Buildings in Risk Category III buildings and other structures whose primary occupancies are public assembly with an occupancy load greater than 300.

    8-706.1.3 All deviations from the detailing provisions of the lateral-force-resisting systems shall be evaluated for stability and the ability to maintain load-carrying capacity at the expected inelastic deformations.

    8-706.2 Existing building performance. The seismic resistance may be based upon the ultimate capacity of the structure to perform, giving due consideration to ductility and reserve strength of the lateral-force-resisting system and materials while maintaining a reasonable factor of safety. Broad judgment may be exercised regarding the strength and performance of materials not recognized by regular code requirements. (See Chapter 8-8, Archaic Materials and Methods of Construction.)

    8-706.2.1 All structural materials or members that do not comply with detailing and proportioning requirements of the regular code shall be evaluated for potential seismic performance and the consequence of non-compliance. All members that would be reasonably expected to fail and lead to collapse or life threatening injury when subjected to seismic demands shall be judged unacceptable, and appropriate structural strengthening shall be developed.

    8-706.3 Load path. A complete and continuous load path, including connections, from every part or portion of the structure to the ground shall be provided for the required forces. It shall be verified that the structure is adequately tied together to perform as a unit when subjected to earthquake forces.

  • CHBC § 8-706.3 High relevance — show source text

    8-706.3 Load path. A complete and continuous load path, including connections, from every part or portion of the structure to the ground shall be provided for the required forces. It shall be verified that the structure is adequately tied together to perform as a unit when subjected to earthquake forces.

    8-706.4 Parapets. Parapets and exterior decoration shall be investigated for conformance with regular code requirements for anchorage and ability to resist prescribed seismic forces.

    An exception to regular code requirements shall be permitted for those parapets and decorations which are judged not to be a hazard to life safety.

    8-706.5 Nonstructural features. Nonstructural features of historical structure, such as exterior veneer, cornices and decorations, which might fall and create a life safety hazard in an earthquake, shall be evaluated. Their ability to resist seismic forces shall be verified, or the feature shall be strengthened with improved anchorage when appropriate.

    8-706.5.1 Partitions and ceilings of corridors and stairways serving an occupant load of 30 or more shall be investigated to determine their ability to remain in place when the building is subjected to earthquake forces.

    8-706.5.2 Seismic forces used to evaluate and improve nonstructural components and their anchorage, where required, shall comply with ASCE 41 or need not exceed 0.75 times the seismic forces prescribed by the requirements of the regular code.

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    8-8 ARCHAIC MATERIALS AND METHODS OF CONSTRUCTION

    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

  • CHBC § 8-705.1 High relevance — show source text

    8-705.1 Gravity loads. The capacity of the structure to resist gravity loads shall be evaluated and the structure strengthened as necessary. The evaluation shall include all parts of the load path. Where no distress is evident, and a complete load path is present, the structure may be assumed adequate by having withstood the test of time if anticipated dead and live loads will not exceed those historically present.

    8-705.2 Wind and seismic loads. The ability of the structure to resist wind and seismic loads shall be evaluated. Wind loads shall be considered when appropriate, but need not exceed 75 percent of the wind loads prescribed by the regular code. The evaluation shall be based on the requirements of Section 8-706.

    8.705.2.1 Any unsafe conditions in the lateral-load-resisting system shall be corrected, or alternative resistance shall be provided. When strengthening is required, additional resistance shall be provided to meet the minimum requirements of the CHBC. The strengthening measures shall be selected with the intent of meeting the performance objectives set forth in Section 8-701.2. The evaluation of structural members and structural systems for seismic loads shall consider the inelastic performance of structural members and their ability to maintain load-carrying capacity during the seismic loadings prescribed by the regular code.

    8.705.2.2 The architect or engineer shall consider additional measures with minimal loss of, and impact to, historical materials which will reduce damage and needed repairs in future earthquakes to better preserve the historical structure in perpetuity. These additional measures shall be presented to the owner for consideration as part of the rehabilitation or restoration.

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    STRUCTURAL REGULATIONS

    SECTION 8-706 — LATERAL LOAD REGULATIONS

    8-706.1 Seismic forces. Strength-level seismic forces used to evaluate the structure for resistance to seismic loads shall be based on the R -values tabulated in the regular code for similar lateral-force-resisting systems including consideration of the structural detailing of the members where such R -values exist. Where such R -values do not exist, an appropriate R -value shall be rationally assigned considering the structural detailing of the members.

    Exceptions:

    1. The forces need not exceed 0.75 times the seismic forces prescribed by the regular code requirements.
    2. For Risk Category I, II or III structures, near-fault increases in ground motion (maximum considered earthquake ground motion of 0.2 second spectral response greater than 150 percent at 5 percent damping) need not be considered when the fundamental period of the building is 0.5 seconds in the direction under consideration.
    3. For Risk Category I or II structures, the seismic base shear need not exceed 0.30W.
    4. For Risk Category III or IV structures, the seismic base shear need not exceed 0.40W.

    8-706.1.1 When a building is to be strengthened with the addition of a new lateral force resisting system, the R -value of the new system can be used when the new lateral force resisting system resists at least 75 percent of the building’s base shear regardless of its relative rigidity.

    8-706.1.2 Evaluation and seismic improvement of unreinforced masonry bearing wall buildings shall comply with the California Existing Building Code (CEBC), Appendix Chapter A1 2013 Edition, and as modified by the CHBC.

    Exceptions:

  • CHBC § 8-7 High relevance — show source text

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    8-7 STRUCTURAL REGULATIONS

    SECTION 8-701 — PURPOSE, INTENT AND SCOPE

    8-701.1 Purpose. The purpose of the CHBC is to provide alternative regulations to the regular code for the structural safety of buildings designated as qualified historical buildings or properties. The CHBC requires enforcing agencies to accept any reasonably equivalent alternatives to the regular code when dealing with qualified historical buildings or properties.

    8-701.2 Intent. The intent of this chapter is to encourage the preservation of qualified historical buildings or structures while providing standards for a minimum level of building performance with the objective of preventing partial or total structural collapse such that the overall risk of life-threatening injury as a result of structural collapse is low.

    8-701.3 Application. The alternative structural regulations provided by Section 8-705 are to be applied in conjunction with the regular code whenever a structural upgrade or reconstruction is undertaken for qualified historical buildings or properties.

    SECTION 8-702 — GENERAL

    8-702.1 The CHBC shall not be construed to allow the enforcing agency to approve or permit a lower level of safety of structural design and construction than that which is reasonably equivalent to the regular code provisions in occupancies which are critical to the safety and welfare of the public at large, including, but not limited to, public and private schools, hospitals, municipal police and fire stations and essential services facilities.

    8-702.2 Nothing in these regulations shall prevent voluntary and partial seismic upgrades when it is demonstrated that such upgrades will improve life safety and when a full upgrade would not otherwise be required.

    SECTION 8-703 — STRUCTURAL SURVEY

    8-703.1 Scope. When a structure or portion of a structure is to be evaluated for structural capacity under the CHBC, it shall be surveyed for structural conditions by an architect or engineer knowledgeable in historical structures. The survey shall evaluate deterioration or signs of distress. The survey shall determine the details of the structural framing and the system for resistance of gravity and lateral loads. Details, reinforcement and anchorage of structural systems and veneers shall be determined and documented where these members are relied on for seismic lateral resistance.

    8-703.2 The results of the survey shall be utilized for evaluating the structural capacity and for designing modifications to the structural system to reach compliance with this code.

    8-703.3 Historical records. Past historical records of the structure or similar structures may be used in the evaluation, including the effects of subsequent alterations.

    SECTION 8-704 — NONHISTORICAL ADDITIONS AND NONHISTORICAL ALTERATIONS

    8-704.1 New nonhistorical additions and nonhistorical alterations which are structurally separated from an existing historical building or structure shall comply with regular code requirements.

    8-704.2 New nonhistorical additions which impose vertical or lateral loads on an existing structure shall not be permitted unless the affected part of the supporting structure is evaluated and strengthened, if necessary, to meet regular code requirements.

    Note: For use of archaic materials, see Chapter 8-8.

    SECTION 8-705 — STRUCTURAL REGULATIONS

  • CHBC § 181.4 High relevance — show source text
    1. Buildings in which the increase in the demand-capacity ratio is due entirely to the addition of rooftop-supported mechanical equipment individually having an operating weight less than 400 pounds (181.4 kg) and where the total additional weight of all rooftop equipment placed after initial construction of the building is less than 10 percent of the roof dead load. For purposes of this exception, “roof” shall mean the roof level above a particular story.
    2. Increases in the demand-capacity ratio due to lateral loads from seismic forces need not be evaluated for the installation of rooftop photovoltaic panel systems where the additional roof dead load due to the system, including ballast where applicable, does not exceed 5 pounds per square foot (psf) (0.2394 kN/m [2] ) and does not exceed 10 percent of the dead load of the existing roof.

    [BS] 503.5 Seismic Design Category F. Where the work area exceeds 50 percent of the building area, and where the building is assigned to Seismic Design Category F, the lateral force-resisting system of the altered building shall meet the requirements of Section 1609 of the California Building Code and Section 304.3.2 of this code. Supports and attachments for nonstructural components serving any portion of the building with a use included in Risk Category IV shall comply with Section 1613 of the California Building Code or shall comply with ASCE 41 using an objective of Position Retention nonstructural performance with the BSE-1E earthquake hazard level.

    [BS] 503.6 Bracing for unreinforced masonry parapets on reroofing. Where the intended alteration requires a permit for reroofing and involves removal of roofing materials from more than 25 percent of the roof area of a building assigned to Seismic Design Category D, E or F that has parapets constructed of unreinforced masonry, the work shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of parapet bracing to resist out-of-plane seismic forces.

    [BS] 503.7 Anchorage for concrete and reinforced masonry walls. Where the work area exceeds 50 percent of the building area, the building is assigned to Seismic Design Category C, D, E or F and the building’s structural system includes concrete or reinforced masonry walls with a flexible roof diaphragm, the alteration shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of wall anchors at the roof line.

    [BS] 503.8 Anchorage for unreinforced masonry walls in major alterations. Where the work area exceeds 50 percent of the building area, the building is assigned to Seismic Design Category C, D, E or F and the building’s structural system includes unreinforced masonry bearing walls, the alteration shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of wall anchors at the floor and roof lines.

    [BS] 503.9 Bracing for unreinforced masonry parapets in major alterations. Where the work area exceeds 50 percent of the building area, and where the building is assigned to Seismic Design Category C, D, E or F, and the building has parapets constructed of unreinforced masonry, the alteration shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of parapet bracing to resist out-of-plane seismic forces.

  • CHBC § 2.3.10. High relevance — show source text

    SECTION A106—MATERIALS REQUIREMENTS

    [BS] A106.1 Condition of existing materials. Existing materials used as part of the required vertical load-carrying or seismic forceresisting system shall be evaluated by on-site investigation and: determined to be in good condition (free of degraded mortar, degraded masonry units or significant cracking); or shall be repaired, enhanced, retrofitted or removed and replaced with new materials. Mortar joint deterioration shall be patched by pointing or repointing of the eroded joint in accordance with Section A106.2.3.10. Existing significant cracks in solid unit unreinforced and solid grouted hollow unit masonry shall be repaired.

    [BS] A106.2 Existing unreinforced masonry.

    [BS] A106.2.1 General. Unreinforced masonry walls used to support vertical loads or seismic forces parallel and perpendicular to the wall plane shall be tested as specified in this section. Masonry that does not meet the minimum requirements established by this chapter shall be repaired, enhanced, removed and replaced with new materials, or alternatively, shall have its structural functions replaced with new materials and shall be anchored to supporting elements.

    [BS] A106.2.2 Lay-up of walls. Unreinforced masonry walls shall be laid in a running bond pattern.

    [BS] A106.2.2.1 Header in multiple-wythe solid brick. The facing and backing wythes of multiple-wythe walls shall be bonded so that not less than 10 percent of the exposed face area is composed of solid headers extending not less than 4 inches (102 mm) into the backing wythes. The clear distance between adjacent header courses shall not exceed 24 inches (610 mm) vertically or horizontally. Where backing consists of two or more wythes, the headers shall extend not less than 4 inches (102 mm) into the most distant wythe, or the backing wythes shall be bonded together with separate headers for which the area and spacing conform to the foregoing. Wythes of walls not meeting these requirements shall be considered to be veneer, and shall not be included in the effective thickness used in calculating the height-to-thickness ratio and the shear capacity strength of the wall. Exception: Where S D 1 is 0.3 g or less, veneer wythes anchored and made composite with backup masonry are permitted to be used for calculation of the effective thickness.

    [BS] A106.2.2.2 Lay-up patterns. Lay-up patterns other than those specified in Section A106.2.2.1 are allowed if their performance can be justified.

    [BS] A106.2.3 Testing of masonry.

    [BS] A106.2.3.1 Concrete masonry units and structural clay load-bearing tile. Grouted or ungrouted hollow concrete masonry units shall be tested in accordance with ASTM C140. Grouted or ungrouted structural clay load-bearing tile shall be tested in accordance with ASTM C67.

    APPENDIX A-6 2025 CALIFORNIA EXISTING BUILDING CODE

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    APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

    [BS] A106.2.3.2 In-place mortar joint shear tests. Mortar joint shear test values, v to, shall be obtained by one of the following:

    1. ASTM C1531.
  • CHBC § 8-804 High 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 § 8-702.2 High relevance — show source text

    8-702.2 Nothing in these regulations shall prevent voluntary and partial seismic upgrades when it is demonstrated that such upgrades will improve life safety and when a full upgrade would not otherwise be required.

    SECTION 8-703 — STRUCTURAL SURVEY

    8-703.1 Scope. When a structure or portion of a structure is to be evaluated for structural capacity under the CHBC, it shall be surveyed for structural conditions by an architect or engineer knowledgeable in historical structures. The survey shall evaluate deterioration or signs of distress. The survey shall determine the details of the structural framing and the system for resistance of gravity and lateral loads. Details, reinforcement and anchorage of structural systems and veneers shall be determined and documented where these members are relied on for seismic lateral resistance.

    8-703.2 The results of the survey shall be utilized for evaluating the structural capacity and for designing modifications to the structural system to reach compliance with this code.

    8-703.3 Historical records. Past historical records of the structure or similar structures may be used in the evaluation, including the effects of subsequent alterations.

    SECTION 8-704 — NONHISTORICAL ADDITIONS AND NONHISTORICAL ALTERATIONS

    8-704.1 New nonhistorical additions and nonhistorical alterations which are structurally separated from an existing historical building or structure shall comply with regular code requirements.

    8-704.2 New nonhistorical additions which impose vertical or lateral loads on an existing structure shall not be permitted unless the affected part of the supporting structure is evaluated and strengthened, if necessary, to meet regular code requirements.

    Note: For use of archaic materials, see Chapter 8-8.

    SECTION 8-705 — STRUCTURAL REGULATIONS

    8-705.1 Gravity loads. The capacity of the structure to resist gravity loads shall be evaluated and the structure strengthened as necessary. The evaluation shall include all parts of the load path. Where no distress is evident, and a complete load path is present, the structure may be assumed adequate by having withstood the test of time if anticipated dead and live loads will not exceed those historically present.

    8-705.2 Wind and seismic loads. The ability of the structure to resist wind and seismic loads shall be evaluated. Wind loads shall be considered when appropriate, but need not exceed 75 percent of the wind loads prescribed by the regular code. The evaluation shall be based on the requirements of Section 8-706.

    8.705.2.1 Any unsafe conditions in the lateral-load-resisting system shall be corrected, or alternative resistance shall be provided. When strengthening is required, additional resistance shall be provided to meet the minimum requirements of the CHBC. The strengthening measures shall be selected with the intent of meeting the performance objectives set forth in Section 8-701.2. The evaluation of structural members and structural systems for seismic loads shall consider the inelastic performance of structural members and their ability to maintain load-carrying capacity during the seismic loadings prescribed by the regular code.

    8.705.2.2 The architect or engineer shall consider additional measures with minimal loss of, and impact to, historical materials which will reduce damage and needed repairs in future earthquakes to better preserve the historical structure in perpetuity. These additional measures shall be presented to the owner for consideration as part of the rehabilitation or restoration.

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    STRUCTURAL REGULATIONS

  • CHBC § 503.7 High relevance — show source text

    [BS] 503.7 Anchorage for concrete and reinforced masonry walls. Where the work area exceeds 50 percent of the building area, the building is assigned to Seismic Design Category C, D, E or F and the building’s structural system includes concrete or reinforced masonry walls with a flexible roof diaphragm, the alteration shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of wall anchors at the roof line.

    [BS] 503.8 Anchorage for unreinforced masonry walls in major alterations. Where the work area exceeds 50 percent of the building area, the building is assigned to Seismic Design Category C, D, E or F and the building’s structural system includes unreinforced masonry bearing walls, the alteration shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of wall anchors at the floor and roof lines.

    [BS] 503.9 Bracing for unreinforced masonry parapets in major alterations. Where the work area exceeds 50 percent of the building area, and where the building is assigned to Seismic Design Category C, D, E or F, and the building has parapets constructed of unreinforced masonry, the alteration shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of parapet bracing to resist out-of-plane seismic forces.

    [BS] 503.10 Anchorage of unreinforced masonry partitions in major alterations. Where the work area exceeds 50 percent of the building area, or where the building is assigned to Seismic Design Category C, D, E or F, and the building has unreinforced masonry partitions and nonstructural walls, the alteration work shall include evaluation of the existing condition or removal, anchoring or alteration of any such partitions or walls within the work area and adjacent to egress paths from the work area, to comply with Section 304.3.2.

    [BS] 503.11 Substantial structural alteration. Where the work area exceeds 50 percent of the building area and where work involves a substantial structural alteration, the lateral load-resisting system of the altered building shall satisfy the requirements of Section 1609 of the California Building Code and Section 304.3.2 of this code. Where the building is assigned to Seismic Design Category D or F, supports and attachments for nonstructural components required to serve any portion of the building with a use included in Risk Category IV shall comply with Section 1613 of the California Building Code or shall comply with ASCE 41 using an objective of Position Retention nonstructural performance with the BSE-1E earthquake hazard level.

    Exceptions:

    1. Buildings of Group R occupancy with not more than five dwelling or sleeping units used solely for residential purposes that are altered based on the conventional light-frame construction methods of the California Building Code or in compliance with the provisions of the California Residential Code .
    2. Where the intended alteration involves structural components of the lowest story of a building, only the lateral loadresisting system above that story need not comply with this section.

    [BS] 503.12 Roof diaphragms resisting wind loads in high-wind regions. Where the intended alteration requires a permit for reroofing and involves removal of roofing materials from more than 50 percent of the roof diaphragm of a building or section of a building located where the basic wind speed, V, is greater than 130 mph (58 m/s) in accordance with Figure 1609.3(2) of the California

  • CHBC § 8-801 High 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 § 906.2 High relevance — show source text

    [BS] 906.2 Existing structural elements resisting lateral loads. Where work involves a substantial structural alteration,the lateral load-resisting system of the altered building shall be shown to satisfy the requirements of Section 1609 of the California Building Code and Section 304.3.2 of this code. Where the building is assigned to Seismic Design Category D or F, supports and attachments for nonstructural components required to serve any portion of the building with a use included in Risk Category IV shall comply with Section 1613 of the California Building Code or shall comply with ASCE 41 using an objective of Position Retention nonstructural performance with the BSE-1E earthquake hazard level.

    Exceptions:

    1. Buildings of Group R occupancy with not more than five dwelling or sleeping units used solely for residential purposes that are altered based on the conventional light-frame construction methods of the California Building Code or in compliance with the provisions of the California Residential Code .
    2. Where the intended alteration involves only the lowest story of a building, structural components of the lateral load resisting system above that story need not comply with this section.

    [BS] 906.3 Seismic Design Category F. Where the building is assigned to Seismic Design Category F, the lateral force-resisting system of the altered building shall meet the requirements of Section 1609 of the California Building Code and Section 304.3.2 of this code. Supports and attachments for nonstructural components serving any portion of the building with a use included in Risk Cate- gory IV shall comply with Section 1613 of the California Building Code or shall comply with ASCE 41 using an objective of Position Retention nonstructural performance with the BSE-1E earthquake hazard level.

    [BS] 906.4 Anchorage for concrete and masonry buildings. For any building assigned to Seismic Design Category D, E or F with a structural system that includes concrete or reinforced masonry walls with a flexible roof diaphragm, the alteration shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of wall anchors at the roof line of all subject buildings and at the floor lines of unreinforced masonry.

    [BS] 906.5 Anchorage for unreinforced masonry walls. For any building assigned to Seismic Design Category C, D, E or F with a structural system that includes unreinforced masonry bearing walls, the alteration shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of wall anchors at the roof line.

    [BS] 906.6 Bracing for unreinforced masonry parapets. Parapets constructed of unreinforced masonry in buildings assigned to Seismic Design Category C, D, E or F shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of parapet bracing.

    [BS] 906.7 Anchorage of unreinforced masonry partitions. Where the building is assigned to Seismic Design Category C, D, E or F, unreinforced masonry partitions and nonstructural walls within the work area and adjacent to egress paths from the work area shall have their existing conditions evaluated or shall be anchored, removed or altered to resist out-of-plane seismic forces to comply with Section 304.3.2.

    SECTION 907—ENERGY CONSERVATION

    907.1 Minimum requirements. Level 3 alterations to existing buildings or structures shall comply with applicable provisions of the California Energy Code (Part 6, Title 24, C.C.R).

  • CHBC § 906.5 High relevance — show source text

    [BS] 906.5 Anchorage for unreinforced masonry walls. For any building assigned to Seismic Design Category C, D, E or F with a structural system that includes unreinforced masonry bearing walls, the alteration shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of wall anchors at the roof line.

    [BS] 906.6 Bracing for unreinforced masonry parapets. Parapets constructed of unreinforced masonry in buildings assigned to Seismic Design Category C, D, E or F shall comply with Section 304.3.2 by evaluation of the existing condition or by installation of parapet bracing.

    [BS] 906.7 Anchorage of unreinforced masonry partitions. Where the building is assigned to Seismic Design Category C, D, E or F, unreinforced masonry partitions and nonstructural walls within the work area and adjacent to egress paths from the work area shall have their existing conditions evaluated or shall be anchored, removed or altered to resist out-of-plane seismic forces to comply with Section 304.3.2.

    SECTION 907—ENERGY CONSERVATION

    907.1 Minimum requirements. Level 3 alterations to existing buildings or structures shall comply with applicable provisions of the California Energy Code (Part 6, Title 24, C.C.R).

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    ALTERATIONS—LEVEL 3

    SECTION 908—EMERGENCY RESPONDER COMMUNICATIONS ENHANCEMENT SYSTEM COVERAGE

    908.1 Emergency responder communication enhancement system coverage. The existing building shall undergo an evaluation of the emergency responder communication signal strength and coverage area within the entire building in accordance with Sections 908.1.1 and 908.1.2.

    Exception: Where it is determined by the fire code official that the emergency responder communication enhancement system (ERCES) is not needed.

    908.1.1 Evaluation. The evaluation shall determine the current signal strength and coverage capabilities of the public safety communication systems utilized by the jurisdiction, measured at the exterior of the building.

    908.1.2 Compliance. The evaluation report shall be submitted for approval by the fire code official and the frequency license holder. Where the coverage area, signal strength or DAQ does not comply with Section 510 of the California Fire Code, the existing building shall be provided with ERCES coverage. The fire code official is authorized to establish the timeframe for such installation or modification.

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    9-6 2025 CALIFORNIA EXISTING BUILDING CODE

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    CALIFORNIA EXISTING BUILDING CODE – MATRIX ADOPTION TABLE

    CHAPTER 10 – CHANGE OF OCCUPANCY

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

Frequently asked questions

What section of the CHBC controls URM retrofits?

The controlling CHBC provision is § 8-706.1.2, which directs that URM bearing‑wall buildings be evaluated and improved per CEBC Appendix Chapter A1 (2013 edition), as modified by the CHBC.

Do I always have to test the masonry?

Not always. CHBC § 8-805.1 permits treating good‑condition solid masonry as 9 psi ultimate shear without testing when unsupported height/length : thickness ≤ 13 and joints/units are in good condition. Otherwise, CEBC Appendix A1 testing is required under CHBC § 8-706.1.2.

If tests show mortar shear lower bound < 30 psi, what must be done?

If the lower bound mortar shear strength (mean − 1σ) is < 30 psi, CEBC Appendix A1 requires pointing and retesting or replacing/anchoring the wall — this procedure is applied by the CHBC per § 8-706.1.2.

Can I use a different retrofit standard instead of CEBC Appendix A1?

Yes — the CHBC allows alternative standards on a case‑by‑case basis when approved by the authority having jurisdiction (AHJ), per the exceptions to § 8-706.1.2.

Who must perform the survey and testing?

A licensed architect or structural engineer knowledgeable about historic structures must perform the structural survey and interpret testing; this is required by § 8-703.1 and applied to the URM evaluation required by § 8-706.1.2.

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