CHBC · California Historical Building Code
How should deterioration, framing details and the load path be documented?
A licensed architect or engineer must inspect and record any deterioration, the sizes and connections of framing members, the location and condition of anchors/reinforcement, and draw the complete load path from roof/floors down to the foundation. This documentation lets the designer decide whether the historic structure can be assumed adequate or what strengthening is necessary under the CHBC.
Last reviewed: July 6, 2026
What the code requires — 2–4 sentences
The CHBC requires a qualified architect or engineer to perform a structural survey that documents deterioration, the details of structural framing and the system for resistance of gravity and lateral loads; where members are relied on for seismic lateral resistance their reinforcement and anchorage must be determined and documented (§ 8-703.1) . The structure’s capacity to resist gravity loads must be evaluated and the evaluation must include all parts of the load path; if no distress is evident and a complete load path exists, the CHBC allows assuming adequacy provided anticipated dead and live loads do not exceed historical values (§ 8-705.1) .
The single most important requirement: document observed deterioration, show the full framing details and connections, and trace a complete and continuous load path from every structural element to the ground so the designer can evaluate gravity and lateral capacity (see § 8-703.1 and § 8-705.1) .
Requirements in detail
Who must do the work
- The survey shall be performed by an architect or engineer knowledgeable in historical structures — bolded requirement in § 8-703.1 .
What to document (minimum)
- Deterioration or signs of distress: rot, corrosion, cracking, settlement, voids, spalled masonry — record location, extent and probable cause (§ 8-703.1) .
- Details of structural framing: member sizes, species/materials, connections, fastener types and spacings, diaphragm construction and continuity (§ 8-703.1) .
- System for resistance of gravity and lateral loads: identify diaphragms, collectors, shear walls, braced frames, foundations and how loads flow between them (§ 8-703.1 and § 8-705.1) .
- Reinforcement and anchorage where members are relied on for seismic lateral resistance: document existing anchors, anchor spacing, embedment, corrosion condition and any supplemental ties (§ 8-703.1) .
Decision-relevant dimensions, values and thresholds
- The CHBC does not replace structural analysis; it requires documentation so capacity can be assessed. The table below summarizes the decision inputs the CHBC explicitly requires to be documented or considered.
| Decision dimension / value | What to show in the record | Code Reference |
|---|---|---|
| Presence/extent of deterioration | Location, type (rot, corrosion, cracks), percent of section loss, photos and measured dimensions | § 8-703.1 |
| Framing member details | Sizes, spacing, species/material, connections, fastener type & spacing | § 8-703.1 |
| Load-path elements | Diaphragms, collectors, shear walls/braces, columns, foundations and their connections | § 8-703.1, § 8-705.1 |
| Reinforcement & anchorage | Existing anchors, tie-rods, embedment depth, corrosion, spacing, connection details | § 8-703.1 |
| Assumption of adequacy | Documented only if no distress and complete load path exists and anticipated loads ≤ historical loads | § 8-705.1 |
| Use of historical records | Past drawings/repairs may be used to support the evaluation | § 8-703.3 |
How to document connections and load path
- Provide clear plan and section sketches or photos with annotated arrows showing the load flow from roof/floors to foundation.
- Show connection details (e.g., beam-to-post, diaphragm-to-wall, anchor type/spacing), with measured fastener spacing and condition. This is required where those members are part of the lateral-resisting system (§ 8-703.1) .
- Verify and show continuity (a complete and continuous load path) from the element to ground; the CHBC emphasizes that every part or portion of the structure must have this path to resist required forces (§ 8-705.1, related § 8-706.3) .
Reporting format and level of detail
- The CHBC requires a professional survey report adequate to evaluate structural capacity and to design modifications as needed — include narratives, annotated plans, photos, measured dimensions, material descriptions and recommendations (§ 8-703.2, § 8-703.1) .
- For archaic materials, testing or assigned allowable strengths must be supported and documented per Section 8-804 and related provisions; the survey must document reinforcement, anchorage and deterioration to support assigned allowable stresses .
Exceptions & special cases
- If no distress is evident and a complete load path is present, CHBC allows assuming gravity resistance adequacy if anticipated dead and live loads will not exceed those historically present (i.e., historic performance may be accepted) (§ 8-705.1) .
- Historical records (old drawings, prior reports) may supplement the survey but do not replace a site inspection; they may be used to evaluate effects of prior alterations (§ 8-703.3) .
- Archaic materials and methods: where historic materials remain, allowable values and assumptions must be supported by the survey and tests where appropriate (see § 8-804) .
- For lateral loads the CHBC has modified force limits and evaluation bases (see Section 8-706); these affect how much strengthening may be required and what forces the documented load path must resist (see § 8-706.1 and § 8-706.3) .
Common mistakes
- Failing to document connections: listing member sizes but not the fastener type/spacing or connector condition (CHBC requires anchorage detail where relied on for lateral resistance, § 8-703.1) .
- Tracing only vertical elements and ignoring diaphragm/collector paths — a complete load path includes diaphragms and collectors, not just walls and columns (§ 8-705.1 and related § 8-706.3) .
- Assuming adequacy without documenting “no distress” or without comparing anticipated loads to historical loads (the CHBC permits the assumption only when both conditions are met, § 8-705.1) .
- Overlooking veneer anchorage and corrosion of anchors; Section 8-811 requires investigation of veneer anchors and corrosion where veneers participate in lateral resistance .
- Treating historical material strengths as code values without documenting tests or justification per the archaic materials chapter (§ 8-804) .
Worked example — small historic townhouse (illustrative)
This example illustrates documenting and applying the CHBC rules; the CHBC sets the documentation requirements but does not specify these numeric examples — they are illustrative only.
Scenario: 2-story historic townhouse with wood-framed floors and a roof. The project engineer must evaluate gravity capacity and document the load path for lateral resistance.
Field survey findings (documented): roof sheathing: 3/4" tongue-and-groove decking; joists 2x10 @ 16" o.c.; exterior wood sill anchored with old 1/2" bolts at ~6 ft o.c.; some sill plates show 20% section rot at two locations; diaphragm nailing is 8d nails at 6" o.c. at edges and 12" o.c. in field; shear walls are historic plaster-over-lath with embedded studs and sporadic horizontal blocking. (All items photographed and dimensioned in report per § 8-703.1) .
Load-path documentation: Annotated plan shows roof -> roof joists -> wall top plate -> wall studs -> sill plate -> foundation. Lateral load path diagrams show diaphragm chords collecting into wall studs and down to foundation; connections are sketched with measured fastener types and spacings (required by § 8-703.1 and to evaluate gravity capacity under § 8-705.1) .
Use of CHBC allowance: Because the survey documents small, localized rot but otherwise a complete load path and no system-wide distress, the engineer may determine that the structure has historically carried typical residential live loads. If the proposed use remains similar and anticipated live loads do not increase, the CHBC allows assuming adequacy for gravity loads — but the rot locations must be repaired or strengthened where they reduce load-carrying capacity (per § 8-705.1) .
If any diaphragm or anchor is found corroded or missing where the lateral system relies on it, the CHBC requires documentation and strengthening/anchorage be provided as needed because reinforcement/anchorage must be determined and documented where relied on for seismic lateral resistance (§ 8-703.1) .
Note: the CHBC does not provide the numeric live-load limits in § 8-703.1/8-705.1 — the example uses common engineering loads for illustration; the controlling code language requires the documentation and evaluation steps shown above .
Related provisions
- § 8-706.3 — Load path: requires a complete and continuous load path including connections from every part to the ground (related to § 8-705.1) .
- § 8-703.3 — Historical records: past records may be used in the evaluation and for effects of alterations (supports documentation) .
- § 8-804 — Allowable conditions for specific (archaic) materials: survey must document reinforcement, anchorage and deterioration to establish allowable stresses .
- § 8-807.1 — Existing wood diaphragms: requires the survey to determine fastener details and spacings and verify a load path through floor construction .
- § 8-811.1 / 8-811.2 — Veneers and anchorage: investigate veneer anchors and corrosion where veneers are relied on for lateral resistance .
Code references
Grounded in the retrieved California Historical Building Code — click a citation to read the verbatim passage:
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 § 319.1.3 High relevance — show source text
319.1.3 For state-owned and community college buildings, where unreinforced masonry is not bearing, it may be used only to resist applied lateral loads. Where unreinforced masonry walls are part of the structure they must be assessed for stability under the applicable nonstructural evaluation procedure.
319.1.4 Public schools. [DSA-SS] For public schools, unreinforced masonry shall not be used to resist in-plane or out-of-plane seismic forces or superimposed gravity loads.
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PROVISIONS FOR ALL COMPLIANCE METHODS
319.1.5 Public schools. [DSA-SS] Wood horizontal diaphragms and wood vertical shear walls shall consist of either diagonal lumber sheathing or structural panel sheathing. Braced horizontal diaphragms may be acceptable when approved by DSA. Straight lumber sheathing may be used as diaphragms or shear walls only when overlain with structural panel sheathing. Let-in bracing, plaster (stucco), hollow clay tile, gypsum wallboard and particleboard sheathing shall not be relied upon to resist seismic forces.
319.2 Existing conditions. The existing condition and properties of the entire structure must be determined and documented by thorough inspection of the structure and site, review of all available related construction documents, review of geotechnical and engineering geologic reports, and performance of necessary testing and investigation. Where samples from the existing structure are taken or in situ tests are performed, they shall be selected and interpreted in a statistically appropriate manner to ensure that the properties determined and used in the evaluation or design are representative of the conditions and structural circumstances likely to be encountered in the structure as a whole. Adjacent structures or site features that may affect the retrofit design shall be identified.
The entire load path of the seismic-force-resisting system shall be determined, documented and evaluated. The load path includes all the horizontal and vertical elements participating in the structural response: such as diaphragms, diaphragm chords, diaphragm collectors, vertical elements such as walls frames, braces; foundations and the connections between the components and elements of the load path. Repaired or retrofitted elements and the standards under which the work was constructed shall be identified.
Data collection in accordance with ASCE 41 shall meet the following minimum levels: 1. [BSC] For state-owned buildings, the requirements shall be met following the data collection requirements of ASCE 41, Section 6.2.
2. [DSA-SS, DSA-SS/CC] For public schools and community college buildings constructed in conformance with the Field Act, visual condition assessment and usual material testing is required unless a more extensive level is required by ASCE 41, Section 6.2.
3. [DSA-SS, DSA-SS/CC] For public schools and community college buildings not constructed in conformance with the Field Act, comprehensive condition assessment and material testing is required, unless a more extensive level is required by ASCE 41, Section 6.2.
Concrete material requirements and testing for public school and community college buildings shall also comply with Sections 1911A and 1909.5 of the California Building Code, respectively.
CHBC § 8-706.1.3 High relevance — show source text
Exceptions:
- 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.
- 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.
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
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 § 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:
- The forces need not exceed 0.75 times the seismic forces prescribed by the regular code requirements.
- 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.
- For Risk Category I or II structures, the seismic base shear need not exceed 0.30W.
- 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 § 8-706.3 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 § 8-706 Medium 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:
- The forces need not exceed 0.75 times the seismic forces prescribed by the regular code requirements.
- 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.
- For Risk Category I or II structures, the seismic base shear need not exceed 0.30W.
- 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:
- 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.
- 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 § 8-806.4 Medium 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 § 8-807.3 Medium relevance — show source text
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
The hand-built, untested use of wrought or black iron, the use of cast iron or grey iron, and the myriad of joining methods that are not specifically allowed by code may be used wherever applicable and wherever they have proven their worth under the considerable span of years involved with most qualified historical buildings or structures. Uplift capacity should be evaluated and strengthened where necessary. Fixed conditions or midheight lateral loads on cast iron columns that could cause failure should be taken into account. Existing structural wrought, forged steel or grey iron may be assigned the maximum working stress prevalent at the time of original construction.
SECTION 8-810 — HOLLOW CLAY TILE
The historical performance of hollow clay tile in past earthquakes shall be carefully considered in evaluating walls of hollow clay tile construction. Hollow clay tile bearing walls shall be evaluated and strengthened as appropriate for lateral loads and their ability to maintain support of gravity loads. Suitable protective measures shall be provided to prevent blockage of exit stairways, stairway enclosures, exit ways and public ways as a result of an earthquake.
SECTION 8-811 — VENEERS
8-811.1 Terra cotta and stone. Terra cotta, cast stone and natural stone veneers shall be investigated for the presence of suitable anchorage. Steel anchors shall be investigated for deterioration or corrosion. New or supplemental anchorage shall be provided as appropriate.
8-811.2 Anchorage. Brick veneer with mechanical anchorage at spacings greater than required by the regular code may remain, provided the anchorages have not corroded. Nail strength in withdrawal in wood sheathing may be utilized to its capacity in accordance with code values.
SECTION 8-812 — GLASS AND GLAZING
CHBC § 8-805.3 Medium 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.
- One-story adobe load-bearing walls shall not exceed a height-to-thickness ratio of 6.
- 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 § 8-602.2 Medium relevance — show source text
Such documentation shall be in accordance
with Section 8-602.2, Item 2, and shall include the opinion and comments of state or
local accessibility officials, and the opinion and comments of representative local
groups of people with disabilities. Such documentation shall be retained in the
permanent file of the enforcing agency. Copies of the required documentation should
be available at the facility upon request.
** Note:**For commercial facilities and places of public accommodation
(Title III entities).
Equivalent facilitation for an element of a building or property when applied as a waiver
of an ADA accessibility requirement will not be entitled to the Federal Department of
Justice certification of this code as rebuttable evidence of compliance for that element.|Applies|Waivers
If a builder
applies for a
waiver of an ADA
accessibility
requirement for
an element of a
building, he or
she will not be
entitled to
certification’s
rebuttable
evidence of
compliance for
that element. This
limitation on the
certification
determination
should be noted
in any publication
of Chapter 8-6 if
certification is
granted.|Applies| |**Notes:**The regular code for Chapter 8-6 is contained in Title 24, Part 2, Vol.1, Chapter 11B, which contain standards for new construction.
Provisions of this chapter may be used in conjunction with all other provisions of the regular code and ADA regulations.|**Notes:**The regular code for Chapter 8-6 is contained in Title 24, Part 2, Vol.1, Chapter 11B, which contain standards for new construction.
Provisions of this chapter may be used in conjunction with all other provisions of the regular code and ADA regulations.|**Notes:**The regular code for Chapter 8-6 is contained in Title 24, Part 2, Vol.1, Chapter 11B, which contain standards for new construction.
Provisions of this chapter may be used in conjunction with all other provisions of the regular code and ADA regulations.|**Notes:**The regular code for Chapter 8-6 is contained in Title 24, Part 2, Vol.1, Chapter 11B, which contain standards for new construction.
Provisions of this chapter may be used in conjunction with all other provisions of the regular code and ADA regulations.|26 2025 CALIFORNIA HISTORICAL BUILDING CODE
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HISTORY NOTE APPENDIX
2025 California Historical Building Code California Code of Regulations, Title 24, Part 8
HISTORY:
For prior history, see the History Note Appendix to the California Historical Building Code, 2022 Triennial Edition, effective January 1, 2023.
- Adoption of the 2025 California Historical Building Code, CCR Title 24, Part 8, carrying forward existing amendments from the 2022 edition. Effective on January 1, 2026.
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CBC § A203 Medium relevance — show source text
[BS] A202.1 Scope. The provisions of this chapter shall apply to wall anchorage systems that resist out-of-plane forces and to collectors in existing reinforced concrete or reinforced masonry buildings with flexible diaphragms. Wall anchorage systems that were designed and constructed in accordance with the 1997 Uniform Building Code or the 2001 or subsequent editions of the California Building Code shall be deemed to comply with these provisions.
SECTION A203—DEFINITIONS
[BS] A203.1 Definitions. For the purpose of this chapter, the applicable definitions in the California Building Code and the following shall apply:
[BS] CONTINUITY CONNECTOR. A component, typically a plate, rod, strap or hold-down, that ensures load path continuity along the full length of a crosstie or strut.
[BS] CROSSTIE. A member or group of members continuous across the main diaphragm that connects opposite wall lines and transfers out-of-plane wall anchorage forces into the diaphragm.
[BS] FLEXIBLE DIAPHRAGM. A roof or floor sheathed with plywood, wood decking (1-by or 2-by) or metal deck without a concrete topping slab.
[BS] STRUT. A member or group of members continuous across a subdiaphragm that transfers out-of-plane wall anchorage forces into the subdiaphragm.
[BS] WALL ANCHORAGE SYSTEM. The components comprising a complete load path for out-of-plane wall forces from the wall to the main diaphragm, typically including anchors embedded in or fastened to the wall; rods, straps, plates, hold-downs or other hardware; subdiaphragms and their chords; crossties; struts; and continuity connectors.
[BS] WALL SEGMENT. Any length of concrete wall with continuous horizontal reinforcing and not interrupted or intersected by a pilaster or vertical construction joint, or any length of reinforced masonry wall with continuous horizontal reinforcing and not interrupted or intersected by a pilaster or vertical control joint.
SECTION A204—SYMBOLS AND NOTATIONS
[BS] A204.1 General. For the purpose of this chapter, the applicable symbols and notations in the California Building Code shall apply.
SECTION A205—GENERAL REQUIREMENTS
[BS] A205.1 General. The seismic-resisting elements specified in this chapter shall comply with applicable provisions of Section 1613 of the California Building Code and Chapter 12 of ASCE 7, except as modified herein.
[BS] A205.2 Requirements for plans. The plans shall accurately reflect the results of the engineering investigation and design and shall show all pertinent dimensions and sizes for plan review and construction. The following shall be provided:
- Floor plans and roof plans shall show existing framing construction, diaphragm construction, proposed wall anchors, crossties and collectors. Existing nailing, anchors, crossties and collectors shall be shown on the plans if they are considered part of the lateral force-resisting systems.
- Typical wall panel details and sections with panel thickness, height, pilasters and location of anchors shall be provided.
- Details shall include existing and new anchors and the method of developing anchor forces into the diaphragm framing, existing and new crossties, and existing and new or improved support of roof and floor girders at pilasters or walls.
- The basis for design and the building code used for the design shall be stated on the plans.
Frequently asked questions
Who must perform the structural survey required by § 8-703.1?
An architect or engineer knowledgeable in historical structures must perform the survey and document deterioration, framing and load-resisting systems as required by § 8-703.1 .
Can I assume an older building is adequate without tests?
Only if no distress is evident and a complete load path is present, and anticipated dead/live loads will not exceed historical values — this limited assumption is allowed by § 8-705.1, otherwise evaluate and strengthen as necessary .
What level of detail is required for connections?
Document connector type, spacing, embedment and condition (corrosion, section loss) with annotated details or photos when those members are part of the lateral-resisting system; this is required by § 8-703.1 .
Do I need to test archaic materials?
If archaic materials are relied on, allowable strengths should be supported by testing or rational assignment and documented per the CHBC; the structural survey must document reinforcement, anchorage and deterioration to support those assignments (see § 8-804) .
Is diaphragm nail spacing important?
Yes — the survey must determine fastener details and spacings and verify diaphragms as part of the load path (see § 8-807.1) .
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