CHBC · California Historical Building Code
How are strength values and engineering approaches for archaic materials assigned?
For homeowners: the CHBC lets historic materials stay if a qualified architect or structural engineer inspects and either uses CHBC tables or tests to set safe strength limits — you won’t be forced to meet modern material specs unless testing or safety requires it.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
The CHBC requires that strength values for archaic materials be assigned either by comparison to similar conventional codified materials or by testing, and that archaic construction be investigated per the required structural survey. The design professional (the architect or structural engineer in responsible charge) assigns allowable stresses or strength levels, and assigned values must not exceed those given in the CHBC without adequate testing and enforcing‑agency concurrence. See § 8-802.
The single most important rule: assign archaic‑material strength based on similar codified materials or tests, document the actual construction via the structural survey, and have the responsible architect/engineer set allowable strengths subject to the enforcing agency. § 8-802.
Requirements in detail
Who decides the values
- The architect or structural engineer in responsible charge must assign allowable stresses or strength levels for archaic materials, based on investigation and tests as applicable. § 8-802.
Investigation and testing
- A thorough investigation of the archaic materials and their construction details is required in accordance with the structural survey provisions (the CHBC requires documentation of existing conditions, reinforcement, anchorage, deterioration, etc.). See § 8-802 and § 8-703.
- Where testing is appropriate, the architect/engineer must base assigned strengths on representative tests of the existing materials (e.g., concrete sampling, masonry pull tests). Assigned values that exceed CHBC tabulated values require “adequate testing.” § 8-802.
Limiting principle
- Assigned strength values “shall not be greater than those provided for in the following sections without adequate testing” and are “subject to the concurrence of the enforcing agency.” § 8-802.
Decision‑relevant dimensions and numbers
| Decision item | Typical value / rule to use | Code reference |
|---|---|---|
| Basis for assignment | Use values for similar conventional codified materials, or derive from tests | § 8-802 |
| Structural survey requirement | Document condition, reinforcement, anchorage, deterioration before assigning values | § 8-703 (referenced by § 8-802) |
| Existing solid masonry (unreinforced) — maximum ultimate shear allowed without testing | 9 pounds per square inch (psi) (62.1 kPa) when inspection shows filled joints and reasonably good brick & mortar and height/length:thickness ratio ≤ 13 | § 8-805.1 |
| Existing adobe — maximum shear allowed | 12 psi (82.7 kPa) | § 8-806.7 |
| Wood fasteners (square/cut nails) — shear allowance | Square/cut nails may be used with up to 50% increase in shear capacity over wire nails | § 8-807.3 |
| Tabulated shear capacities for diaphragms, crosswalls, etc. | See CHBC Table 8‑8A / Table 8‑8B (e.g., 1,500 lb/ft for some floor diaphragms; 1,800 lb/ft for other cases) | Table 8‑8A / Table 8‑8B (CHBC chapter) |
| Combined shear values (table note) | Shear values of combined materials may be combined but the total combined value shall not exceed 900 lb/ft (13,140 N/m) | Table 8‑8A notes |
| Requirement for testing to exceed tabulated values | Must perform adequate testing and obtain enforcing agency concurrence before assigning higher values | § 8-802 |
How testing is used
- Tests establish representative strength for the population of materials and inform bond, development lengths, and other detailing. For concrete and masonry, the CHBC references normal test practices and the CEBC for test protocols. § 8-802, § 8-808.1, and the references in § 8-805.
Interaction with seismic/lateral evaluation
- When evaluating lateral resistance, the CHBC allows rational assignment of R‑values or use of similar codified R‑values, and permits seismic forces not to exceed 0.75 times those of the regular code in some nonstructural cases. Broad judgment is allowed regarding materials not recognized by the regular code; but members likely to fail and cause collapse must be strengthened. See § 8-706 and the CHBC chapter on archaic materials.
Exceptions & special cases
- Assigned values that exceed CHBC tabulated limits require adequate testing and enforcing‑agency concurrence — no unilateral upward adjustments by the design professional. § 8-802.
- For existing solid masonry the 9 psi shear limit applies only where: an inspection report supports good brick and mortar, joints are filled, and the unsupported height/length to thickness ratio does not exceed 13. Shear may be increased by 10% for axial stress from wall weight. § 8-805.1.
- Stone masonry and other masonry types may be treated like solid brick masonry only when representative testing and inspection verify the required interlock/ties; otherwise different testing procedures apply. § 8-805.2.
- Concrete of low strength and with less reinforcement than modern code may remain, but the architect/engineer must assign strengths based on testing and determine bond/development requirements from tests or historical data. § 8-808.1–8-808.2.
Common mistakes
- Assuming “aged” materials automatically require modern code values — the CHBC explicitly allows historical materials to be used with assigned values based on similarity or testing; do not uncritically force modern codified values without following § 8‑802 procedures. § 8-802.
- Using tabulated CHBC values without performing the required structural survey documentation (condition, reinforcement, anchorage, deterioration). The structural survey is the prerequisite before assigning strengths. § 8-703 (referenced by § 8-802).
- Exceeding a CHBC numeric cap (e.g., 9 psi for solid masonry, 12 psi for adobe) without representative sampling/testing and enforcing‑agency concurrence. § 8-805.1, § 8-806.7, § 8-802.
- Forgetting to consider detailing consequences (ductility, reserve strength, anchorage) when assigned strengths differ from modern detailing requirements; the engineer must evaluate detailing implications. § 8-808.2.
Worked example — concrete scenario with numbers
Scenario: You are evaluating an existing unreinforced solid brick bearing wall in a qualified historic building. Wall thickness = 12 inches, wall is in generally good condition per inspection, mortar joints filled, and unsupported height/length to thickness ratio = 10 (≤ 13).
Steps and numbers:
- CHBC allows a maximum ultimate shear of 9 psi for existing solid masonry without testing when inspection criteria are met. § 8-805.1.
- Compute available shear capacity per linear foot of wall (1 ft height): shear area = wall thickness × 1 ft = 12 in × 12 in = 144 in². Capacity = 9 psi × 144 in² = 1,296 lb per linear foot. § 8-805.1.
- If seismic or lateral demand (based on the evaluation procedure) produces a shear demand of 800 lb/ft, compare: 1,296 lb/ft available > 800 lb/ft demand → wall acceptable in shear without additional testing or strengthening, subject to the architect/engineer documenting the structural survey and the enforcing agency concurrence per § 8-802.
- If the engineer wishes to claim a higher shear value (say 13 psi) rather than 9 psi, representative testing is required and the increase must be supported by test data and accepted by the enforcing agency. § 8-802.
Related provisions
- § 8-703 — Structural survey: documentation of existing conditions that the engineer must use to assign strengths.
- § 8-804 — Allowable conditions for specific materials: evaluation details for materials to remain.
- § 8-805.1 — Existing solid masonry shear value (9 psi) and conditions.
- § 8-806.7 — Existing adobe shear value (12 psi) and related adobe provisions.
- § 8-807.3 — Existing wood framing and fastener allowances (square/cut nails +50% shear).
- § 8-808.1–8-808.2 — Concrete: testing, assigned strengths, and detailing implications.
- Table 8‑8A / Table 8‑8B — Tabulated strength values for existing and new materials used with existing construction (diaphragm and shear values).
- § 8-706 — Lateral load regulations and guidance on seismic evaluation and R‑values when archaic systems are evaluated.
Code references
Grounded in the retrieved California Historical Building Code — click a citation to read the verbatim passage:
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 § 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 § 8-807.3 High 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 § 8-806.4 High relevance — show source text
8-806.4 Nonload-bearing adobe. Nonload-bearing adobe partitions and gable end walls shall be evaluated for stability and anchored against out-of-plane failure if necessary.
8-806.5 Bond beam. Where provided, a bond beam or equivalent structural element shall be located at the top of all adobe walls, and at the second floor for two-story buildings or structures. The size and configuration of the structural element shall be sufficient to provide an effective brace for the wall, to tie the building together and to connect the wall to the floor or roof.
8-806.6 Repair or reconstruction. Repair or reconstruction of wall area may utilize unstabilized brick or adobe masonry designed to be compatible with the constituents of the existing adobe materials.
8-806.7 Shear values. Existing adobe may be allowed a maximum strength level of 12 pounds per square inch (82.7 kPa) for shear.
8-806.8 Mortar. Mortar may be of the same soil composition as that used in the existing wall, or in new walls as necessary to be compatible with the adobe brick.
SECTION 8-807 — WOOD
8-807.1 Existing wood diaphragms or walls. Existing wood diaphragms or walls of straight or diagonal sheathing shall be assigned shear resistance values appropriate with the fasteners and materials functioning in conjunction with the sheathing. The structural survey shall determine fastener details and spacings and verify a load path through floor construction. Shear values of Tables 8-8-A and 8-8-B.
8-807.2 Wood lath and plaster. Wood lath and plaster walls and ceilings may be utilized using the shear values referenced in Section 8-807.1.
8-807.3 Existing wood framing. Existing wood framing members may be assigned allowable stresses consistent with codes in effect at the time of construction. Existing or new replacement wood framing may be of archaic types originally used if properly researched, such as balloon and single wall. Wood joints such as dovetail and mortise and tenon types may be used structurally, provided they are well made. Lumber selected for use and type need not bear grade marks, and greater or lesser species such as low-level pine and fir, boxwood and indigenous hardwoods and other variations may be used for specific conditions where they were or would have been used.
Wood fasteners such as square or cut nails may be used with a maximum increase of 50 percent over wire nails for shear.
SECTION 8-808 — CONCRETE
8-808.1 Materials. Natural cement concrete, unreinforced rubble concrete and similar materials may be utilized wherever that material is used historically. Concrete of low strength and with less reinforcement than required by the regular code may remain in place. The architect or engineer shall assign appropriate values of strength based on testing of samples of the materials. Bond and development lengths shall be determined based on historical information or tests.
8-808.2 Detailing. The architect or engineer shall carefully evaluate all detailing provisions of the regular code which are not met and shall consider the implications of these variations on the ultimate performance of the structure, giving due consideration to ductility and reserve strength.
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SECTION 8-809 — STEEL AND IRON
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:
- 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 § 3.1. High relevance — show source text
Gypsum wallboard, blocked edges|Per side: 600 lbs per foot for seismic shear
550 lbs per foot for seismic shear
200 lbs per foot for seismic shear
400 lbs per foot for seismic shear| |3. Existing footings, wood framing, structural steel and reinforcing steel
3.1. Plain concrete footings
3.2. Douglas fir wood
3.3. Reinforcing steel
3.4. Structural steel|f ′c = 1,500 psi (10.34 MPa) unless otherwise shown by
tests3
Allowable stress same as D.F. No. 13
_ft _= 40,000 lbs per square inch (124.1 N/mm2) maximum
ft= 33,000 lbs per square inch (137.9 N/mm2) maximum| |1. Material must be sound and in good condition.
2. Shear values of these materials may be combined, except the total combined value shall not exceed 900 pounds per foot (13,140 N/m).
3. Stresses given may be increased for combinations of loads as specified in the regular code.|1. Material must be sound and in good condition.
2. Shear values of these materials may be combined, except the total combined value shall not exceed 900 pounds per foot (13,140 N/m).
3. Stresses given may be increased for combinations of loads as specified in the regular code.|2025 CALIFORNIA HISTORICAL BUILDING CODE 17
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ARCHAIC MATERIALS AND METHODS OF CONSTRUCTION
TABLE 8-8B—STRENGTH VALUES OF NEW MATERIALS USED IN CONNECTION WITH EXISTING CONSTRUCTION Col2 NEW MATERIALS OR CONFIGURATIONS OF MATERIALS STRENGTH LEVEL CAPACITY1 1. Horizontal diaphragms2
1.1. 15/32 inch minimum plywood sheathing fastened directly over existing straight
sheathing with edges of plywood located on center of individual sheathing
boards and fastened with minimum #8x 11/4 inch wood screws or nails with
helical threads 0.13 inch min. diameter and 11/4 inch min. length at 4 inch
centers all panel edges and 12 inch centers each way in field
1.2. Same plywood and attachments as 1.1 fastened directly over existing diago-
nal sheathing
1.3. 3/8 inch plywood sheathing fastened directly over existing straight or diagonal
sheathing with ends and edges on centers of individual sheathing boards and
fastened with #6 wood screws or nails with helical threads 0.13 inch min.
diameter and 11/4 inch min. length at 6 inch centers tall panel edges and 12
inch centers each way in field1,500 lbs per foot
1,800 lbs per foot
900 lbs per foot2. Shear walls:
Plywood sheathing applied directly over wood studs. No value shall be given to
plywood applied over existing plaster or wood sheathing100 percent of the value specified in the regular code for
shear walls3. Crosswalls: (special procedure only)
3.1. Plywood sheathing applied directly over wood studs.CHBC § 8-8 High relevance — show source text
CHAPTER 8-8 ARCHAIC MATERIALS AND METHODS OF
CONSTRUCTION . . . . . . . . . . . . . . . . . . . . . . . 15
Section
8-801 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 15 8-802 General Engineering Approaches. . . . . . . . . . . . . . . . . 15 8-803 Nonstructural Archaic Materials. . . . . . . . . . . . . . . . . . 15
8-804 Allowable Conditions for Specific Materials . . . . . . . 15 8-805 Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 8-806 Adobe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8-807 Wood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8-808 Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8-809 Steel and Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8-810 Hollow Clay Tile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8-811 Veneers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8-812 Glass and Glazing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
CHAPTER 8-9 MECHANICAL, PLUMBING AND ELECTRICAL REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . 19
Section
8-901 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 19 8-902 Mechanical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8-903 Plumbing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 8-904 Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
CHAPTER 8-10 QUALIFIED HISTORICAL DISTRICTS,
SITES AND OPEN SPACES . . . . . . . . . . . . . . . 23
Section
CHBC § 8-6 High relevance — show source text
CHAPTER 8-6 ACCESSIBILITY . . . . . . . . . . . . . . . . . . . . . . . . 11
Section
8-601 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 11
8-602 Basic Provisions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8-603 Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8-604 Equivalent Facilitation. . . . . . . . . . . . . . . . . . . . . . . . . . 12
CHAPTER 8-7 STRUCTURAL REGULATIONS. . . . . . . . . . . . . 13
Section
8-701 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 13 8-702 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8-703 Structural Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8-704 Nonhistorical Additions and
Nonhistorical Alterations . . . . . . . . . . . . . . . . . . . . . . . 13
8-705 Structural Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8-706 Lateral Load Regulations. . . . . . . . . . . . . . . . . . . . . . . . 14
CHAPTER 8-8 ARCHAIC MATERIALS AND METHODS OF
CONSTRUCTION . . . . . . . . . . . . . . . . . . . . . . . 15
Section
8-801 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 15 8-802 General Engineering Approaches. . . . . . . . . . . . . . . . . 15 8-803 Nonstructural Archaic Materials. . . . . . . . . . . . . . . . . . 15
8-804 Allowable Conditions for Specific Materials . . . . . . . 15 8-805 Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 8-806 Adobe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8-807 Wood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8-808 Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
CHBC § 8-705.1 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.
2025 CALIFORNIA HISTORICAL BUILDING CODE 13
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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 § 8-804 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.
2025 CALIFORNIA HISTORICAL BUILDING CODE 15
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ARCHAIC MATERIALS AND METHODS OF CONSTRUCTION
8-805.2.3 Testing of stone masonry. Testing of stone masonry shall be similar to the 2010 CEBC requirements for brick masonry, except that representative stones which are not interlocked shall be pulled outward from the wall and shear area appropriately calculated after the test.
CHBC § 0.63 High relevance — show source text
Staples shall have a minimum crown width of7/16 inch and shall be installed with their crowns parallel to the long dimension of the framing members.
i. For shear loads of normal or permanent load duration as defined by the ANSI/AWC NDS, the values in the table shall be multiplied by 0.63 or 0.56, respectively.|For SI: 1 inch = 25.4 mm, 1 pound per foot = 14.5939 N/m.
a. For framing of other species: (1) Find specific gravity for species of lumber in ANSI/AWC NDS. (2) For staples find shear value from table for Structural I panels (regardless of
actual grade) and multiply value by 0.82 for species with specific gravity of 0.42 or greater, or 0.65 for all other species.
b. Panel edges backed with 2-inch nominal or wider framing. Install panels either horizontally or vertically. Space fasteners maximum 6 inches on center along intermediate
framing members for3/8-inch and7/16-inch panels installed on studs spaced 24 inches on center. For other conditions and panel thickness, space fasteners maximum 12 inches
on center on intermediate supports.
c. 3/8-inch panel thickness or siding with a span rating of 16 inches on center is the minimum recommended where applied directly to framing as exterior siding. For grooved
panel siding, the nominal panel thickness is the thickness of the panel measured at the point of fastening.
d. Framing at adjoining panel edges shall be 3 inches nominal or wider.
e. Values apply to all-veneer plywood. Thickness at point of fastening on panel edges governs shear values.
f. Where panels are applied on both faces of a wall and fastener spacing is less than 6 inches on center on either side, panel joints shall be offset to fall on different framing
members, or framing shall be 3 inches nominal or thicker at adjoining panel edges.
g. In Seismic Design Category D, E or F, where shear design values exceed 350 pounds per linear foot, all framing members receiving edge fastening from abutting panels shall be
not less than a single 3-inch nominal member, or two 2-inch nominal members fastened together in accordance with Section 2306.1 to transfer the design shear value
between framing members. Wood structural panel joint and sill plate nailing shall be staggered at all panel edges. See AWC SDPWS for sill plate size and anchorage
requirements.
h. Staples shall have a minimum crown width of7/16 inch and shall be installed with their crowns parallel to the long dimension of the framing members.
i. For shear loads of normal or permanent load duration as defined by the ANSI/AWC NDS, the values in the table shall be multiplied by 0.63 or 0.56, respectively.|CHBC § 19.1 Medium relevance — show source text
3 / 4 -inch-diameter (19.1 mm) bolts: 60 foot pounds (81.3 N-m).
[BS] A107.5.3 Prequalification test for bolts and other types of anchors. ASTM E488 or the test procedure in Section A107.5.1 is permitted to be used to determine tension or shear strength values for anchors greater than those permitted by Table A108.1(2). Anchors shall be installed in the same manner and using the same materials as will be used in the actual construction. Not fewer than five tests for each bolt size and type shall be performed for each class of masonry in which they are proposed to be used. The tension and shear strength values for such anchors shall be the lesser of the average ultimate load divided by 5.0 or the average load at which [1] / 8 inch (3.2 mm) elongation occurs for each size and type of anchor and class of masonry.
SECTION A108—DESIGN STRENGTHS
[BS] A108.1 Strength values.
- Strength values for existing materials are given in Table A108.1(1) and for new materials in Table A108.1(2).
- The strength reduction factor, φ, shall be taken equal to 1.0.
APPENDIX A-8 2025 CALIFORNIA EXISTING BUILDING CODE
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APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS
- The use of materials not specified herein shall be based on substantiating research data or engineering judgment, as approved by the code official.
[BS] TABLE A108.1(1)—STRENGTH VALUES FOR EXISTING MATERIALS Col2 Col3 EXISTING MATERIALS OR CONFIGURATION OF MATERIALSa EXISTING MATERIALS OR CONFIGURATION OF MATERIALSa STRENGTH VALUES EXISTING MATERIALS OR CONFIGURATION OF MATERIALSa EXISTING MATERIALS OR CONFIGURATION OF MATERIALSa × 14.594 for N/m Horizontal diaphragms Roofs with straight sheathing and roofing applied directly to the
sheathing.300 lbs. per ft. for seismic shear Horizontal diaphragms Roofs with diagonal sheathing and roofing applied directly to the
sheathing.750 lbs. per ft. for seismic shear Horizontal diaphragms Floors with straight tongue-and-groove sheathing. 300 lbs. per ft. for seismic shear Horizontal diaphragms Floors with straight sheathing and finished wood flooring with board
edges offset or perpendicular.1,500 lbs. per ft. for seismic shear Horizontal diaphragms Floors with diagonal sheathing and finished wood flooring. 1,800 lbs. per ft. for seismic shear Horizontal diaphragms Metal deck welded with minimal welding.c 1,800 lbs. per ft. for seismic shear Horizontal diaphragms Metal deck welded for seismic resistance.d 3,000 lbs. per ft. for seismic shear Crosswallsb Plaster on wood or metal lath. 600 lbs. per ft. for seismic shear Crosswallsb Plaster on gypsum lath. 550 lbs. per ft. for seismic shear Crosswallsb Gypsum wallboard, unblocked edges. 200 lbs. per ft.
Frequently asked questions
Who must sign off on assigned archaic‑material strengths?
The architect or structural engineer in responsible charge assigns the allowable stresses; assigned values are subject to the enforcing agency’s concurrence. § 8-802.
Can I just use modern code values for an historic wall?
No — CHBC expects assigned values to be based on similar codified materials or tests, and the structural survey must document the actual condition first. Don’t substitute modern values without justification and testing. § 8-802 and § 8-703.
What numeric limits exist I should know immediately?
Common caps include 9 psi ultimate shear for unreinforced solid masonry (non‑adobe) and 12 psi for adobe unless testing supports otherwise. §§ 8-805.1, 8-806.7.
Do I always need laboratory testing?
Not always — if the CHBC tabulated values apply and are supported by a thorough structural survey and inspection, testing may not be required. But if you want to assign higher strengths than the CHBC tables, representative testing is required. § 8-802.
Where are diaphragm and shear tabulated values found?
Look in Table 8‑8A and Table 8‑8B of Chapter 8‑8 for common diaphragm and shear values used with existing construction. Use those as allowed references when applicable. Table 8‑8A/B (CHBC).
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