CHBC · California Historical Building Code

What shear values apply to existing wood diaphragms, lath and plaster assemblies?

In plain terms for a homeowner: the California Historical Building Code lets engineers use fixed shear values for many existing wood floors, roofs, and plaster‑on‑lath walls (see Table 8‑8A), but only after a qualified structural survey confirms the actual sheathing, nails/staples and a continuous load path; some combinations are limited (a combined cap appears in the table), and if any element is deteriorated the table values don’t apply until repaired or justified.

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

Existing wood diaphragms and wood lath and plaster assemblies are assigned specific allowable shear resistance values in the CHBC; the designer must verify actual fastener types, spacings and a continuous load path before using those values. The controlling rule is § 8-807.1 (existing wood diaphragms or walls) and § 8-807.2 (wood lath and plaster assemblies), which point to the strength tables (see Table 8‑8A) for the numeric values.

The single most important rule: Assign shear values only after a structural survey verifies the fasteners, spacing and load path, and then apply the shear capacities shown in Table 8‑8A (per § 8‑807.1 and § 8‑807.2).

Requirements in detail

  • Defined terms (first use):

    • Shear resistance — the lateral (in‑plane) capacity of a diaphragm or wall, typically given in pounds per foot (plf) in Table 8‑8A. Shear resistance values in the CHBC are assigned to assemblies on the basis of observed materials and fasteners.
    • Wood diaphragm — an existing roof or floor sheathing assembly acting to distribute lateral forces to vertical resisting elements; values are found in Table 8‑8A as referenced by § 8‑807.1.
    • Wood lath and plaster — plaster applied over wood (or metal) lath; § 8‑807.2 authorizes use of the shear values referenced in § 8‑807.1.

  • What § 8‑807.1 requires (plain): perform a structural survey to determine fastener types and spacing, verify the load path through floor (or roof) construction, and then assign shear resistance values from the CHBC tables (Table 8‑8A and Table 8‑8B where applicable).

  • What § 8‑807.2 requires (plain): wood lath & plaster walls and ceilings may be used for lateral resistance using the shear values referenced by § 8‑807.1 (i.e., the same tables).

Decision‑relevant shear values (quick reference)

The most-used numerical values are published in Table 8‑8A (Strength Values for Existing Materials). The table below reproduces the decision‑relevant assemblies and their shear values as shown in the CHBC (units: pounds per foot for seismic shear). Code Reference column shows the CHBC table/section where the value appears.

Assembly / configuration Shear value (plf) Code Reference
Roof — straight sheathing with roofing applied directly 300 plf Table 8‑8A (per § 8‑807.1)
Roof — diagonal sheathing with roofing applied directly 750 plf Table 8‑8A (per § 8‑807.1)
Floor — straight tongue‑and‑groove sheathing 300 plf Table 8‑8A (per § 8‑807.1)
Floor — straight sheathing with finished wood flooring (board edges offset or perpendicular) 1,500 plf Table 8‑8A (per § 8‑807.1)
Floor — diagonal sheathing with finished wood flooring 1,800 plf Table 8‑8A (per § 8‑807.1)
Crosswall — plaster on wood or metal lath (per side) 600 plf Table 8‑8A (per § 8‑807.1)
Crosswall — plaster on gypsum lath (per side) 550 plf Table 8‑8A (per § 8‑807.1)
Crosswall — gypsum wallboard, unblocked edges 200 plf Table 8‑8A (per § 8‑807.1)
Crosswall — gypsum wallboard, blocked edges 400 plf Table 8‑8A (per § 8‑807.1)

Notes from the CHBC table:

  • Material must be sound and in good condition to use these values.
  • Shear values of these materials may be combined, but the total combined value shall not exceed 900 pounds per foot (13,140 N/m) per the Table notes. This table note is part of Table 8‑8A in the CHBC.

(If you need the complete raw tables or Table 8‑8B, that portion was not returned in the retrieval I used — see caveat below.)

Exceptions & special cases

  • The CHBC requires a structural survey to document fastener types and spacings and to verify an actual load path before applying table values; you cannot simply assume the table value without the survey (see § 8‑807.1).
  • Table note limiting total combined shear to 900 plf may restrict how multiple materials’ shear contributions are added together. The CHBC text in Table 8‑8A includes that cap; the code does not expand the note into longer guidance in the retrieved text, so interpretation (for combinations that include diaphragm values larger than 900 plf) should be resolved with engineering judgment and the enforcing agency.
  • If fasteners are degraded, missing or non‑original (or if sheathing is not sound), the table values are not permitted unless the condition is corrected or justified by testing/analysis. The CHBC explicitly conditions values on material being “sound and in good condition.”
  • § 8‑807.1 references both Table 8‑8A and Table 8‑8B; the retrieval supplied Table 8‑8A but the specific Table 8‑8B content was not available in the files I searched. If your assembly should be evaluated against Table 8‑8B, obtain that table from the CHBC or the enforcing agency.

Common mistakes

  • Relying on the table numbers without performing the required structural survey (fastener type, spacing, and load path) — the CHBC requires verification first (§ 8‑807.1).
  • Confusing per‑side values for crosswalls with diaphragm (in‑plane) values or mixing units (these are in plf — pounds per foot).
  • Improperly summing shear contributions from multiple materials and exceeding the 900 plf cap in the table note (the cap is in Table 8‑8A).
  • Using diaphragm values from the regular CBC tables without checking the CHBC allowance and the required survey; CHBC specifically points designers to its own tables for existing historical materials.

Worked example — concrete scenario

Scenario: You are evaluating an existing floor diaphragm with straight sheathing and finished wood flooring with board edges offset (historic assembly), and the span of the diaphragm you are checking is 12 feet along the lateral load path.

  1. Verify the assembly in the structural survey: confirm sheathing type, fastener type & spacing, condition of sheathing and nailing, and that the load path connects the diaphragm to the vertical resisting element (per § 8‑807.1).
  2. Table lookup: the CHBC Table 8‑8A gives 1,500 plf for that assembly.
  3. Capacity calculation: shear capacity = 1,500 plf × 12 ft = 18,000 lb available seismic shear capacity for that length of diaphragm (subject to verified fasteners and condition).
  4. Combining with other elements: if you attempt to add a contributing crosswall value (for example plaster on wood lath = 600 plf per side), remember the Table note that combined values may not exceed 900 plf. The CHBC table note must be observed; therefore do not simply add 1,500 + 600 without reconciling that with the table note and confirming what the cap is intended to limit (see Exception & special cases above).

Related provisions (CHBC)

  • § 8‑807 — Wood (general heading and context for the wood provisions).
  • § 8‑807.1 — Existing wood diaphragms or walls (structural survey requirement; points to Tables 8‑8A and 8‑8B).
  • § 8‑807.2 — Wood lath and plaster (authorizes use of the shear values referenced in § 8‑807.1).
  • Table 8‑8A — Strength Values for Existing Materials (contains the numerical shear values and table notes discussed above).
  • § 8‑703 — Structural Survey (chapter reference that establishes the need for a survey to document conditions for historic buildings).

If you need scans/exact printed layout of Table 8‑8A or the missing Table 8‑8B, or want me to compute capacities for a specific plan geometry (with verified fastener spacings), tell me the assembly details and dimensions and I will compute step‑by‑step using the CHBC values. Note: Table 8‑8B content was not present in the files I retrieved; consult your CHBC copy or the enforcing agency for that table.

Code references

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

  • 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.

    16 2025 CALIFORNIA HISTORICAL BUILDING CODE

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    ARCHAIC MATERIALS AND METHODS OF CONSTRUCTION

    SECTION 8-809 — STEEL AND IRON

  • CHBC § 2306.3 High relevance — show source text

    WOOD

    TABLE 2306.3(3)—ALLOWABLE SHEAR VALUES FOR WIND OR SEISMIC FORCES FOR SHEAR WALLS OF LATH
    AND PLASTER OR GYPSUM BOARD WOOD FRAMED WALL ASSEMBLIES UTILIZING STAPLES    		 Col2 Col3 Col4 Col5 Col6
    TYPE OF MATERIAL THICKNESS OF
    MATERIAL    		 WALL
    CONSTRUCTION    		 **STAPLE SPACINGb **
    MAXIMUM (inches)    		 SHEAR VALUEa, c
    (plf)    		 MINIMUM
    STAPLE SIZEf, g
    1. Expanded metal or
    woven wire lath and
    Portland cement
    plaster    		 7/8″ Unblocked 6 180 No. 16 gage galv.
    staple,7/8″ legs
    2. Gypsum lath, plain
    or perforated    		 3/8″ lath and
    1/2″ plaster    		 Unblocked 5 100 No. 16 gage galv.
    staple, 11/8″ long
    3. Gypsum sheathing 1/2″ × 2′ × 8′ Unblocked 4 75 No. 16 gage galv.
    staple, 13/4″ long
    3. Gypsum sheathing 1/2″ ×4′ Blockedd
    Unblocked    		 4
    7    		 175
    100    		 175
    100
    4. Gypsum board,
    gypsum veneer base
    or water-resistant
    gypsum backing
    board    		 1/2″ Unblockedd 7 75 No. 16 gage galv.
    staple, 11/2″ long
    4. Gypsum board,
    gypsum veneer base
    or water-resistant
    gypsum backing
    board    		 1/2″ Unblockedd 4 110 110
    4. Gypsum board,
    gypsum veneer base
    or water-resistant
    gypsum backing
    board    		 1/2″ Unblocked 7 100 100
    4. Gypsum board,
    gypsum veneer base
    or water-resistant
    gypsum backing
    board    		 1/2″ Unblocked 4 125 125
    4. Gypsum board,
    gypsum veneer base
    or water-resistant
    gypsum backing
    board    		 1/2″ Blockede 7 125 125
    4. Gypsum board,
    gypsum veneer base
    or water-resistant
    gypsum backing
    board    		 1/2″ Blockede 4 150 150
    4. Gypsum board,
    gypsum veneer base
    or water-resistant
    gypsum backing
    board    		 5/8″ Unblockedd 7 115 No. 16 gage galv.
    staple, 15/8″ long
    4. Gypsum board,
    gypsum veneer base
    or water-resistant
    gypsum backing
    board    		 5/8″ Unblockedd 4 145 145
    4.
  • CHBC § 8-805.3 High relevance — show source text

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

    SECTION 8-806 — ADOBE

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

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

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

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

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

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

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

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

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

    SECTION 8-807 — WOOD

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

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

  • CHBC § 25.4 High relevance — show source text

    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. for seismic shear| |Crosswallsb|Gypsum wallboard, blocked edges.|400 lbs. per ft. for seismic shear| |Existing footing, wood framing,
    structural steel, reinforcing
    steel|Plain concrete footings.|f′c = 1,500 psi unless otherwise
    shown by tests| |Existing footing, wood framing,
    structural steel, reinforcing
    steel|Douglas fir wood.|Same as D.F. No. 1| |Existing footing, wood framing,
    structural steel, reinforcing
    steel|Reinforcing steel.|Fy = 40,000 psi maximum| |Existing footing, wood framing,
    structural steel, reinforcing
    steel—continued|Structural steel.|Fy = 33,000 psi maximum| |For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 pound = 4.4 N, 1 pound per square inch = 6894.75 N/m2, 1 pound per foot = 14.43 N/m.
    a. Material must be sound and in good condition.
    b. Shear values of these materials may be combined, except the total combined value should not exceed 900 pounds per foot.
    c. Minimum 22-gage steel deck with welds to supports satisfying the standards of the Steel Deck Institute.
    d. Minimum 22-gage steel deck with3/4-inch diameter plug welds at an average spacing not exceeding 8 inches and with sidelap welds appropriate for the deck span.|For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 pound = 4.4 N, 1 pound per square inch = 6894.75 N/m2, 1 pound per foot = 14.43 N/m.
    a. Material must be sound and in good condition.
    b. Shear values of these materials may be combined, except the total combined value should not exceed 900 pounds per foot.
    c. Minimum 22-gage steel deck with welds to supports satisfying the standards of the Steel Deck Institute.
    d.

  • CHBC § 0.82 High relevance — show source text

    For framing of other species: (1) Find specific gravity for species of framing
    lumber in ANSI/AWC NDS. (2) For staples, multiply the shear value from the table by 0.82 for species with specific gravity of 0.42 or greater, or 0.65 for all other species.
    c. Values shown are for fiberboard sheathing on one side only with long panel dimension either parallel or perpendicular to studs.
    d. Fastener shall be spaced 6 inches on center along intermediate framing members.
    e. Values are not permitted in_Seismic Design Category_ D, E or F.|For SI: 1 inch = 25.4 mm, 1 pound per foot = 14.5939 N/m.
    a. Fiberboard sheathing shall not be used to brace concrete or masonry walls.
    b. Panel edges shall be backed with 2-inch or wider framing of Douglas Fir-larch or Southern pine. For framing of other species: (1) Find specific gravity for species of framing
    lumber in ANSI/AWC NDS. (2) For staples, multiply the shear value from the table by 0.82 for species with specific gravity of 0.42 or greater, or 0.65 for all other species.
    c. Values shown are for fiberboard sheathing on one side only with long panel dimension either parallel or perpendicular to studs.
    d. Fastener shall be spaced 6 inches on center along intermediate framing members.
    e. Values are not permitted in_Seismic Design Category_ D, E or F.|

    2025 CALIFORNIA BUILDING CODE 23-31

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    WOOD

    TABLE 2306.3(3)—ALLOWABLE SHEAR VALUES FOR WIND OR SEISMIC FORCES FOR SHEAR WALLS OF LATH
    AND PLASTER OR GYPSUM BOARD WOOD FRAMED WALL ASSEMBLIES UTILIZING STAPLES    		 Col2 Col3 Col4 Col5 Col6
    TYPE OF MATERIAL THICKNESS OF
    MATERIAL    		 WALL
    CONSTRUCTION    		 **STAPLE SPACINGb **
    MAXIMUM (inches)    		 SHEAR VALUEa, c
    (plf)    		 MINIMUM
    STAPLE SIZEf, g
    1. Expanded metal or
    woven wire lath and
    Portland cement
    plaster    		 7/8″ Unblocked 6 180 No. 16 gage galv.
    staple,7/8″ legs
    2. Gypsum lath, plain
    or perforated    		 3/8″ lath and
    1/2″ plaster    		 Unblocked 5 100 No. 16 gage galv.
    staple, 11/8″ long
    3. Gypsum sheathing 1/2″ × 2′ × 8′ Unblocked 4 75 No. 16 gage galv.
    staple, 13/4″ long
    3. Gypsum sheathing 1/2″ ×4′ Blockedd
    Unblocked    		 4
    7    		 175
    100    		 175
    100
    4.
  • CHBC § 8-812.1 High relevance — show source text

    8-812.1 Glazing subject to human impact. Historical glazing material located in areas subject to human impact may be approved subject to the concurrence of the enforcing agency when alternative protective measures are provided. These measures may include, but not be limited to, additional glazing panels, protective film, protective guards or systems, and devices or signs which would provide adequate public safety.

    8-812.2 Glazing in fire-rated systems. See Section 8-402.3.

    TABLE8-8A—STRENGTH VALUES FOR EXISTING MATERIALS Col2
    EXISTING MATERIALS OR CONFIGURATIONS OF MATERIALS1 STRENGTH LEVEL CAPACITY
    x14.594 for N/m
    1. Horizontal diaphragms2
    1.1. Roofs with straight sheathing and roofing applied directly to the sheathing
    1.2. Roofs with diagonal sheathing and roofing applied directly to the sheathing
    1.3. Floors with straight tongue-and-groove sheathing
    1.4. Floors with straight sheathing and finished wood flooring with board edges
    offset or perpendicular
    1.5. Floors with diagonal sheathing and finished    		 300 lbs per foot for seismic shear
    750 lbs per foot for seismic shear
    300 lbs per foot for seismic shear
    1,500 lbs per foot for seismic shear
    1,800 lbs per foot for seismic shear
    2. Crosswalls2,3
    2.1. Plaster on wood or metal lath
    2.2. Plaster on gypsum lath
    2.3. Gypsum wallboard, unblocked edges
    2.4. 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

  • CHBC § 19.1 High 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.

    1. Strength values for existing materials are given in Table A108.1(1) and for new materials in Table A108.1(2).
    2. The strength reduction factor, φ, shall be taken equal to 1.0.

    APPENDIX A-8 2025 CALIFORNIA EXISTING BUILDING CODE

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

    APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

    1. 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.
  • CHBC § 25.4 High relevance — show source text

    Shear values of these materials may be combined, except the total combined value should not exceed 900 pounds per foot.
    c. Minimum 22-gage steel deck with welds to supports satisfying the standards of the Steel Deck Institute.
    d. Minimum 22-gage steel deck with3/4-inch diameter plug welds at an average spacing not exceeding 8 inches and with sidelap welds appropriate for the deck span.|For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 pound = 4.4 N, 1 pound per square inch = 6894.75 N/m2, 1 pound per foot = 14.43 N/m.
    a. Material must be sound and in good condition.
    b. Shear values of these materials may be combined, except the total combined value should not exceed 900 pounds per foot.
    c. Minimum 22-gage steel deck with welds to supports satisfying the standards of the Steel Deck Institute.
    d. Minimum 22-gage steel deck with3/4-inch diameter plug welds at an average spacing not exceeding 8 inches and with sidelap welds appropriate for the deck span.|

    [BS] TABLE A108.1(2)—STRENGTH VALUES OF NEW MATERIALS USED IN CONJUNCTION WITH EXISTING CONSTRUCTION Col2 Col3
    NEW MATERIALS OR CONFIGURATION OF MATERIALS NEW MATERIALS OR CONFIGURATION OF MATERIALS STRENGTH VALUES
    Horizontal
    diaphragms    		 Plywood sheathing applied directly over existing straight sheathing
    with ends of plywood sheets bearing on joists or rafters and edges of
    plywood located on center of individual sheathing boards.    		 675 lbs. per ft.
    Crosswalls Plywood sheathing applied directly over wood studs; no value should
    be given to plywood applied over existing plaster or wood sheathing.    		 1.2 times the value specified in the current
    building code.
    Crosswalls Drywall or plaster applied directly over wood studs. The value specified in the current building code.
    Crosswalls Drywall or plaster applied to sheathing over existing wood studs. 50 percent of the value specified in the current
    building code.
    Tension anchorsf Anchors extending entirely through unreinforced masonry wall
    secured with bearing plates on far side of a wall 30 square inches of
    area.b, c    		 5,400 lbs. per anchor for three-wythe minimum
    walls.
    2,700 lbs. for two-wythe walls.
    Shear boltse, f Anchors embedded not less than 8 inches into unreinforced masonry
    walls; anchors should be centered in 21/2-inch-diameter holes with
    dry-pack or nonshrink grout around the circumference of the anchor.    		 The value for plain masonry specified for solid
    masonry TMS 402; and no value larger than
    those given for3/4-inch bolts should be used.
    Combined tension
    and shear anchorsf    		 Through-anchors—anchors meeting the requirements for shear and
    for tension anchors.b, c    		 Tension—same as for tension anchors.
    Shear—same as for shear anchors.
    Combined tension
    and shear anchorsf    		 Embedded anchors—anchors extending to the exterior face of the
    wall with a 21/2-inch round plate under the head and drilled at an
    angle of 221/2 degrees to the horizontal; installed as specified for
    shear anchors.a, b, c    		 Tension—3,
  • CHBC § 0.249 High relevance — show source text

    24
    |0.249
    |0.048
    |–
    | |4.94|0.326|0.063|–| |5.65|0.413|0.080|–| |6.36|0.507|0.098|–| |7.06|0.611|0.118|0.030| |7.77|0.723|0.139|0.035| |8.47|0.843|0.162|0.041| |9.18|0.969|0.187|0.047| |9.89|1.108|0.212|0.053| |10.59|1.252|0.240|0.060| |12.36|1.647|0.315|0.079| |14.12
    |2.090
    |0.398
    |0.100
    | |15.89
    |2.580
    |0.490
    |0.123
    | |17.66|3.116|0.591|0.148| |19.42|–|0.701|0.176| |21.19|–|0.818|0.205| |22.95|–|0.944|0.236| |24.72|–|1.078|0.268| |28.25|–|1.369|0.341| |31.78|–|1.690|0.421| |35.31|–|2.043|0.509| |38.84|–|2.425|0.603| |42.37|–|2.838|0.705| |45.90
    |–
    |3.280
    |0.814
    | |49.43|–|3.751|0.929| |52.97|–|4.249|1.052| |56.50|–|–|1.181| |60.03|–|–|1.318| |63.56|–|–|1.461| |67.09|–|–|1.611| |70.62|–|–|1.768| |81.21|–|–|2.276| |88.28|–|–|2.647| |95.34|–|–|3.044|

    FLOW RATE
    (SCFM)1    		 PRESSURE DROP (psi) PER 100 FEET2 Col3 Col4
    FLOW RATE
    (SCFM)1    		 1⁄2 INCH PIPE 3⁄4 INCH PIPE 1 INCH PIPE
    5.30 0.126 0.024 –
    10.59 0.430 0.082 –
    15.89 0.886 0.168 –
    21.19 1.485 0.281 –
    26.48 2.220 0.419 –
    31.78 3.089 0.581 –
    37.08 4.087 0.766 –
    42.37 – 0.975 –
    47.67 – 1.206 –
    52.97 – 1.460 0.361
    58.26 – 1.736 0.429
    63.56 – 2.033 0.502
    68.85 – 2.
  • CHBC § 8-810 High relevance — show source text

    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

    8-812.1 Glazing subject to human impact. Historical glazing material located in areas subject to human impact may be approved subject to the concurrence of the enforcing agency when alternative protective measures are provided. These measures may include, but not be limited to, additional glazing panels, protective film, protective guards or systems, and devices or signs which would provide adequate public safety.

    8-812.2 Glazing in fire-rated systems. See Section 8-402.3.

    TABLE8-8A—STRENGTH VALUES FOR EXISTING MATERIALS Col2
    EXISTING MATERIALS OR CONFIGURATIONS OF MATERIALS1 STRENGTH LEVEL CAPACITY
    x14.594 for N/m
    1. Horizontal diaphragms2
    1.1. Roofs with straight sheathing and roofing applied directly to the sheathing
    1.2. Roofs with diagonal sheathing and roofing applied directly to the sheathing
    1.3. Floors with straight tongue-and-groove sheathing
    1.4. Floors with straight sheathing and finished wood flooring with board edges
    offset or perpendicular
    1.5. Floors with diagonal sheathing and finished    		 300 lbs per foot for seismic shear
    750 lbs per foot for seismic shear
    300 lbs per foot for seismic shear
    1,500 lbs per foot for seismic shear
    1,800 lbs per foot for seismic shear
    2. Crosswalls2,3
    2.1. Plaster on wood or metal lath
    2.2. Plaster on gypsum lath
    2.3. Gypsum wallboard, unblocked edges
    2.4.
  • CHBC § 7-3 High relevance — show source text

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    CHAPTER 8-8 ARCHAIC MATERIALS AND METHODS OF

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

    Section

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

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

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

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

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

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

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

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

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

    Section

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

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

    CHAPTER 8-10 QUALIFIED HISTORICAL DISTRICTS,

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

    Section

Frequently asked questions

Do I always have to do a structural survey before using these table values?

Yes. § 8‑807.1 explicitly requires a structural survey to identify fastener types/spacings and to verify a load path before assigning shear resistance from the CHBC tables.

Can I combine diaphragm and crosswall shear values to get more capacity?

The Table 8‑8A notes allow combining shear values but state the total combined value shall not exceed 900 plf; apply that restriction and interpret combinations with care — if the combination is critical, resolve with engineering analysis and the enforcing agency.

The table shows 600 plf for plaster on wood lath — is that per side or total?

Table 8‑8A lists 600 plf “per side” for plaster on wood or metal lath crosswalls. Use the per‑side notation as given in the table.

Where are Table 8‑8B values? I can’t find them in the files you used.

§ 8‑807.1 references Tables 8‑8A and 8‑8B, but the retrieval I used included Table 8‑8A only. The CHBC copy at your jurisdiction or the enforcing agency should be consulted for Table 8‑8B.

What if the fasteners are square nails or otherwise archaic?

The CHBC expects the survey to document fastener types; historic fasteners are permitted to be used per the chapter when researched, but their condition and load capacity must be confirmed before using table values (see § 8‑807.1 and related wood provisions).

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Wood, Concrete, Steel & Other Archaic Materials

California Historical Building Code