CHBC · California Historical Building Code
What shear and strength values may be assigned to existing solid (non‑adobe) masonry?
If your building has existing solid (non‑adobe) unreinforced masonry in reasonably good condition, the CHBC lets a licensed architect or engineer assign a maximum ultimate shear of 9 psi provided the unsupported height/length divided by thickness is ≤13 and mortar joints are filled; you may add 10% of the wall’s axial compression from its own weight, or perform CEBC Appendix A tests to justify higher values (see **§ 8-805.1**).
Last reviewed: July 6, 2026
What the code requires — 2–4 sentences
Existing solid masonry (non‑adobe) may be assigned a maximum ultimate shear strength of 9 pounds per square inch (62.1 kPa) without testing provided a registered design professional certifies that an inspection was done, mortar joints are filled, and brick and mortar are reasonably good. This value applies to unreinforced masonry where the maximum ratio of unsupported height or length to thickness does not exceed 13; the allowable shear may be increased by 10 percent of the axial direct stress due to the weight of the wall directly above. See § 8-805.1 for the controlling text.
The simple rule: you can use 9 psi shear for existing solid (non‑adobe) unreinforced masonry if the wall is in reasonably good condition and its unsupported height/length divided by thickness is ≤ 13; add 10% of the axial stress from wall weight if present. § 8-805.1
Requirements in detail
Which walls this applies to
- Applies to existing solid masonry walls of any type except adobe (so adobe is excluded). § 8-805.1
- Applies to unreinforced masonry only for the 9 psi allowance unless testing/other evidence supports a different value. § 8-805.1
Key thresholds and conditions (first‑use bolded)
- Maximum default ultimate shear strength: 9 psi (62.1 kPa) — § 8-805.1.
- Maximum unsupported height or length to thickness ratio: 13 (wall height/length measured to supporting or resisting elements that are at least twice as stiff as the tributary wall; stiffness based on gross section). § 8-805.1.
- Shear may be increased by 10 percent of the axial direct stress due to the weight of the wall directly above. § 8-805.1.
- Higher‑quality mortar can justify greater shear values but must be tested per the CEBC Appendix A (as modified by CHBC). § 8-805.1.
Quick decision table
| Decision factor | Assigned value / limit | Code Reference |
|---|---|---|
| Default maximum ultimate shear strength (existing solid, non‑adobe, unreinforced) | 9 psi (62.1 kPa) | § 8-805.1 |
| Allowable increase for axial compression from wall weight | +10% of axial direct stress (added to shear stress) | § 8-805.1 |
| Height or length : thickness (unsupported) — maximum | 13 | § 8-805.1 |
| Condition to use without testing | Architect/engineer statement: inspection done; mortar joints filled; brick & mortar reasonably good | § 8-805.1 |
| If mortar is higher quality or testing required | Use CEBC Appendix A testing procedures (Appendix A/Chapter A1) to justify higher values | § 8-805.1 (reference to CEBC Appendix A) |
How select or increase values
- Without testing: limit the shear to 9 psi and verify wall geometry/condition per the conditions above. § 8-805.1
- With representative testing (mortars, splitting‑tensile or in‑place shear tests) you may justify higher shear values; the CHBC points to the CEBC (Appendix A, Chapter A1) procedures for test methods and calculations. § 8-805.1
Exceptions & special cases
- Adobe is treated separately — adobe is excluded from the 9 psi allowance (CHBC § 8-806 covers adobe and allows other values). § 8-805.1 and § 8-806.
- If supporting or resisting elements are measured but are not at least twice as stiff as the tributary wall, the height/length‑to‑thickness check in § 8-805.1 may not apply; be conservative or test. § 8-805.1.
- Higher‑quality mortar: the CHBC allows higher shear values only when proven by testing in accordance with CEBC Appendix A (CEBC procedures and sampling/testing requirements). § 8-805.1 and CEBC Appendix A references.
Common mistakes
- Treating adobe as if it were covered by the 9 psi rule — adobe has its own provisions and different allowable shear. § 8-805.1 / § 8-806.
- Using the 9 psi value without verifying the height/length : thickness ≤ 13 limit or without the required architect/engineer qualifying statement. § 8-805.1.
- Forgetting to measure wall height/length to supporting elements that are at least twice as stiff (the code defines stiffness basis); incorrect measurement changes whether the 13:1 limit applies. § 8-805.1.
- Assuming the 9 psi is an allowable working stress — the CHBC phrase is “maximum ultimate strength”; design practice should use appropriate factors and the registered design professional should assign allowable stresses per § 8-802 guidance. § 8-805.1 and § 8-802.
Worked example — apply the rule with numbers
Scenario: an existing unreinforced brick wall (not adobe) has:
- thickness t = 12 in (1.0 ft),
- unsupported height h = 10 ft measured to supporting/resisting elements that are at least twice as stiff as the wall, and
- mortar and brick judged “reasonably good” by the project structural engineer, with all bed joints filled.
Step 1 — check height:length : thickness:
- h/t = 10 ft / 1 ft = 10 → this is ≤ 13, so the 9 psi provision can apply per § 8-805.1.
Step 2 — assign shear strength:
- Use default maximum ultimate shear = 9 psi (62.1 kPa) per § 8-805.1.
Step 3 — consider axial compression allowance:
- Estimate axial direct stress from the weight of wall above (example assumption): masonry unit weight ≈ 120 lb/ft³ (typical, not a CHBC value—state as assumption). Wall section above (height = 10 ft, thickness = 1 ft) gives weight per plan area = 120 × 10 × 1 = 1,200 lb/ft² = 1,200 / 144 = 8.33 psi axial stress. Per § 8-805.1, add 10% of axial direct stress to shear: 0.10 × 8.33 psi = 0.833 psi.
Step 4 — combined shear:
- Default 9.00 psi + 0.833 psi = 9.83 psi (ultimate shear) for this wall, if the architect/engineer has certified the required conditions. § 8-805.1.
Notes:
- The wall weight/density used above is an engineering assumption for illustration only; the CHBC requires the 10 percent addition but does not specify density—use measured or agreed material properties in practice. § 8-805.1.
- If higher shear is desired or mortar quality is better, follow CEBC Appendix A testing procedures to document and justify a higher value. § 8-805.1 (reference to CEBC Appendix A)
Related provisions
- § 8-805 — Masonry chapter header and related context (see § 8-805.1).
- § 8-805.1 — Existing solid masonry (primary controlling section for this topic).
- § 8-806 — Adobe provisions (separate treatment; adobe is excluded from § 8-805.1).
- § 8-802 — General engineering approaches: architect/engineer assigns allowable stresses; testing when applicable.
- CEBC Appendix A (testing and calculations referenced by CHBC for justification of higher values) — see CEBC Appendix A/Chapter A1 testing requirements and equations.
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 § 8-804 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
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
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 § 12.2 High relevance — show source text
P D = Superimposed dead load at the location under consideration, pounds (N). For determination of the rocking shear capacity, dead load at the top of the pier under consideration shall be used.
P D+L = Stress resulting from the dead plus actual live load in place at the time of testing, pounds per square inch (kPa). P test = Splitting tensile test load determined by standard test method ASTM C496, pounds (N). P w = Weight of wall, pounds (N). R = Response modification factor for Ordinary plain masonry shear walls in Bearing Wall System from Table 12.2-1 of ASCE 7, where R = 1.5.
S DS = Design spectral acceleration at short period, in g units. S D1 = Design spectral acceleration at 1-second period, in g units. v a = The shear strength of any URM pier, v m A/1.5 pounds (N). v c = Unit shear strength for a crosswall sheathed with any of the materials given in Table A108.1(1) or Table A108.1(2), pounds per foot (N/m).
v mL = Shear strength of unreinforced masonry, pounds per square inch (kPa). V aa = The shear strength of any URM pier or wall, pounds (N). V ca = Total shear capacity of crosswalls in the direction of analysis immediately above the diaphragm level being investigated, v c L c , pounds (N).
V cb = Total shear capacity of crosswalls in the direction of analysis immediately below the diaphragm level being investigated, v c L c, pounds (N). V p = Shear force assigned to a pier on the basis of its relative shear rigidity, pounds (N). V r = Pier rocking shear capacity of any URM wall or wall pier, pounds (N). v test = Load at incipient cracking for each in-place shear test performed in accordance with Section A106.2.3.6, pounds (N). v tl = Lower bound mortar shear strength, pounds per square inch (kPa). v to = Mortar shear test values as specified in Section A106.2.3.6, pounds per square inch (kPa). v u = Unit shear capacity value for a diaphragm sheathed with any of the materials given in Table A108.1(1) or A108.1(2), pounds per foot (N/m).
CHBC § 4.2. High relevance — show source text
DCR = Demand-capacity ratio specified in Section A111.4.2.
f ′ m = Lower bound masonry compressive strength. f sp = Splitting-tensile strength of masonry. F wx = Force applied to a wall at level x, pounds (N). H = Least clear height of opening on either side of a pier, inches (10 [-3] m).
h/t = Height-to-thickness ratio of URM wall. Height, h, is measured between wall anchorage levels and/or slab-on-grade.
L = Span of diaphragm between shear walls, or span between shear wall and open front, feet (m). L c = Length of crosswall, feet (m). L i = Effective diaphragm span for an open-front building specified in Section A111.8, feet (m). P = Applied force as determined by standard test method of ASTM C496 or ASTM E519, pounds (N).
P D = Superimposed dead load at the location under consideration, pounds (N). For determination of the rocking shear capacity, dead load at the top of the pier under consideration shall be used.
P D+L = Stress resulting from the dead plus actual live load in place at the time of testing, pounds per square inch (kPa). P test = Splitting tensile test load determined by standard test method ASTM C496, pounds (N). P w = Weight of wall, pounds (N). R = Response modification factor for Ordinary plain masonry shear walls in Bearing Wall System from Table 12.2-1 of ASCE 7, where R = 1.5.
S DS = Design spectral acceleration at short period, in g units. S D1 = Design spectral acceleration at 1-second period, in g units. v a = The shear strength of any URM pier, v m A/1.5 pounds (N). v c = Unit shear strength for a crosswall sheathed with any of the materials given in Table A108.1(1) or Table A108.1(2), pounds per foot (N/m).
v mL = Shear strength of unreinforced masonry, pounds per square inch (kPa). V aa = The shear strength of any URM pier or wall, pounds (N). V ca = Total shear capacity of crosswalls in the direction of analysis immediately above the diaphragm level being investigated, v c L c , pounds (N).
CHBC § 63.5 High relevance — show source text
Tension bolts
a. Bolts extending entirely through unreinforced masonry walls secured with
bearing plates on far side of a three-wythe minimum wall with at least 30
square inches (19 350 mm2) of area4,5
b. All thread rod extending to the exterior face of the wall installed in adhesive9|5,400 lbs (24 010 N) per bolt6
2,700 lbs (12 009 N) per bolt for two-wythe walls6
3,600 lbs (16 014 N) per bolt| |5. Shear bolts
Bolts embedded a minimum of 8 inches (203 mm) into unreinforced masonry
walls and centered in a 21/2-inch-diameter (63.5 mm) hole filled with dry-pack or
nonshrink grout. Through bolts with first 8 inches (203 mm) as noted above and
embedded all thread rod as noted in Item 4.b5,7,9|1/2 inch (12.7 mm) diameter = 1,050 lbs (4671 N)6
5/8 inch (15.9 mm) diameter = 1,500 lbs (6672 N)6
3/4 inch (19 mm) diameter = 2,250 lbs (10 008 N)6| |6. Infilled walls
Reinforced masonry infilled openings in existing unreinforced masonry walls.
Provide keys or dowels to match reinforcing.|Same as values specified for unreinforced masonry walls| |7. Reinforced masonry
Masonry piers and walls reinforced per the regular code|Same as values specified in the regular code8| |8. Reinforced concrete
Concrete footings, walls and piers reinforced as specified in the regular code
and designed for tributary loads|Same as values specified in the regular code8| |1. Values are for strength level loads as defined in regular code standards.
2. Values may be adjusted for other fasteners when approved by the enforcing authority.
3. In addition to existing sheathing value.
4. Bolts to be1/2-inch (12.7 mm) minimum diameter.
5. Other bolt sizes, values and installation methods may be used provided a testing program is conducted in accordance with regular code standards. Bolt spacing shall not
exceed 6 feet (1830 mm) on center and shall not be less than 12 inches (305 mm) on center.
6. Other masonry based on tests or other substantiated data.
7. Embedded bolts to be tested as specified in regular code standards.
8. Stresses given may be increased for combinations of loads as specified in the regular code.
9. Adhesives shall be approved by the enforcing agency and installed in accordance with the manufacturer’s recommendations. All drilling dust shall be removed from drilled
holes prior to installation.|1. Values are for strength level loads as defined in regular code standards.
2. Values may be adjusted for other fasteners when approved by the enforcing authority.
3. In addition to existing sheathing value.
4. Bolts to be1/2-inch (12.7 mm) minimum diameter.
5. Other bolt sizes, values and installation methods may be used provided a testing program is conducted in accordance with regular code standards. Bolt spacing shall not
exceed 6 feet (1830 mm) on center and shall not be less than 12 inches (305 mm) on center.
6.CHBC § 2.3.6 High relevance — show source text
[BS] A106.2.3.6 Minimum quality of mortar.
- Mortar shear test values, v to, in pounds per square inch (kPa), shall be obtained for each in-place shear test in accordance with the following equation:
Equation A1-2 v to = ( V test / A b ) - P D+L
where:
V test = Load at first observed movement.
A b = Total area of the bed joints above and below the test specimen.
P D+L = Stress resulting from actual dead plus live loads in place at the time of testing. 2. Individual unreinforced masonry walls with more than 50 percent of mortar test values, v to, less than 30 pounds per square inch (207 kPa) shall be pointed prior to and retested. 3. The lower bound mortar shear strength, v tL, is defined as the mean minus one standard deviation of the mortar shear test values, v to . 4. Unreinforced masonry with mortar shear strength, v tL, less than 30 pounds per square inch (207 kPa) shall be pointed and retested or shall have its structural function replaced, and shall be anchored to supporting elements in accordance with Sections A106.2.1 and A113.8. When existing mortar in any wythe is pointed to increase its shear strength and is retested, the condition of the mortar in the adjacent bed joints of the inner wythe or wythes and the opposite outer wythe shall be examined for extent of deterioration. The shear strength of any wall class shall be not greater than that of the weakest wythe of that class.
[BS] A106.2.3.7 Minimum quality of masonry. Where the alternative procedures of Section A106.2.3.2 are used to determine masonry quality, the following minimums apply:
- The minimum average value of splitting tensile strength, f sp, as calculated by Equation A1-1 shall be 50 pounds per square inch (344.7 kPa).
- Individual unreinforced masonry walls with average splitting tensile strength of less than 50 pounds per square inch (344.7 kPa) shall be pointed and retested.
- The lower-bound mortar strength f spL is defined as the mean minus one standard deviation P D+L of the splitting tensile test values f sp .
[BS] A106.2.3.8 Collar joints. The collar joints shall be inspected at the test locations during each in-place shear test, and estimates of the percentage of surfaces of the adjacent wythe that are covered with mortar shall be reported along with the results of the in-place shear tests.
[BS] A106.2.3.9 Unreinforced masonry classes. Existing unreinforced masonry shall be categorized into one or more classes based on shear strength, quality of construction, state of repair, deterioration and weathering. A class shall be characterized by the masonry shear strength determined in accordance with Section A108.2. Classes are defined for whole walls, not for small areas of masonry within a wall. Discretion in the definition of classes of masonry is permitted to avoid unnecessary testing.
CHBC § 2.3.2. High relevance — show source text
ASTM C1531.
For masonry walls that have high shear strength mortar, or where in-place testing is not practical because of crushing or other failure mode of the masonry, alternative procedures for testing shall be used in accordance with Section A106.2.3.2.
[BS] A106.2.3.3 Alternative procedures for testing masonry. The splitting tensile strength of existing masonry, f sp, or the prism strength of existing masonry, f′ m , is permitted to be determined in accordance with ASTM C496 and calculated by the following equation:
Equation A1-1
fsp = 0.494---------------- a n P -
[BS] A106.2.3.4 Location of tests. The shear tests shall be taken at locations representative of the mortar conditions throughout the building. Test locations shall be determined at the building site by the registered design professional in charge. Results of all tests and their locations shall be recorded.
[BS] A106.2.3.5 Number of tests. The minimum number of tests per masonry class shall be determined as follows:
At each of both the first and top stories, not less than two tests per wall or line of wall elements providing a common line of resistance to seismic forces.
At each of all other stories, not less than one test per wall or line of wall elements providing a common line of resistance to seismic forces.
In any case, not less than one test per 1,500 square feet (139.4 m [2] ) of wall surface and not less than a total of eight tests.
[BS] A106.2.3.6 Minimum quality of mortar.
- Mortar shear test values, v to, in pounds per square inch (kPa), shall be obtained for each in-place shear test in accordance with the following equation:
Equation A1-2 v to = ( V test / A b ) - P D+L
where:
V test = Load at first observed movement.
A b = Total area of the bed joints above and below the test specimen.
P D+L = Stress resulting from actual dead plus live loads in place at the time of testing. 2. Individual unreinforced masonry walls with more than 50 percent of mortar test values, v to, less than 30 pounds per square inch (207 kPa) shall be pointed prior to and retested. 3. The lower bound mortar shear strength, v tL, is defined as the mean minus one standard deviation of the mortar shear test values, v to . 4. Unreinforced masonry with mortar shear strength, v tL, less than 30 pounds per square inch (207 kPa) shall be pointed and retested or shall have its structural function replaced, and shall be anchored to supporting elements in accordance with Sections A106.2.1 and A113.8. When existing mortar in any wythe is pointed to increase its shear strength and is retested, the condition of the mortar in the adjacent bed joints of the inner wythe or wythes and the opposite outer wythe shall be examined for extent of deterioration. The shear strength of any wall class shall be not greater than that of the weakest wythe of that class.
CHBC § 25.4 High relevance — show source text
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—3,600 lbs. per anchor.
Shear—same as for shear anchors.|2025 CALIFORNIA EXISTING BUILDING CODE APPENDIX A-9
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS
[BS] TABLE A108.1(2)—STRENGTH VALUES OF NEW MATERIALS USED IN CONJUNCTION WITH EXISTING CONSTRUCTION—continued Col2 Col3 NEW MATERIALS OR CONFIGURATION OF MATERIALS NEW MATERIALS OR CONFIGURATION OF MATERIALS STRENGTH VALUES Infilled walls Reinforced masonry infilled openings in existing unreinforced
masonry walls; provide keys or dowels to match reinforcing.Same as values specified for unreinforced
masonry walls.Reinforced masonryd Masonry piers and walls reinforced per the current building code. The value specified in the current building
code for strength design.Reinforced concreted Concrete footings, walls and piers reinforced as specified in the
current building code.The value specified in the current building
code for strength design.For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 pound = 4.4 N, 1 degree = 0.017 rad, 1 pound per foot = 14.43 N/m, 1 foot = 304.8 mm.
a. Embedded anchors to be tested as specified in Section A107.4.
b. Anchors shall be1/2 inch minimum in diameter.
c. Drilling for anchors shall be done with an electric rotary drill; impact tools should not be used for drilling holes or tightening anchors and shear bolt nuts.
d. Load factors or capacity reduction factors shall not be used.
e. Other bolt sizes, values and installation methods may be used, provided that a testing program is conducted in accordance with Section A107.5.3. The strength value shall be
determined by multiplying the calculated allowable value, determined in accordance with Section A107.5.3, by 3.0, and the usable value shall be limited to not greater than
1.5 times the value given in the table.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
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
ARCHAIC MATERIALS AND METHODS OF CONSTRUCTION
SECTION 8-809 — STEEL AND IRON
CHBC § 2114A.4 High relevance — show source text
1" CLEARANCE (AIRSPACE) TO COMBUSTIBLE SHEATHING
2113 A .20 Chimney fireblocking. All spaces between chimneys and floors and ceilings through which chimneys pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between wood joists, beams or headers shall be self-supporting or be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.
SECTION 2114 A —DRY-STACK MASONRY
2114 A .1 General. The design of dry-stack masonry structures shall comply with the requirements of Chapters 1 through 8 of TMS 402 except as modified by Sections 2114 A .2 through 2114 A .5.
2114 A .2 Limitations. Dry-stack masonry shall be prohibited in Risk Category IV structures.
2114 A .3 Materials. Concrete masonry units complying with ASTM C90 shall be used.
2114 A .4 Strength. Dry-stack masonry shall be of adequate strength and proportions to support all superimposed loads without exceeding the allowable stresses listed in Table 2114 A .4. Allowable stresses not specified in Table 2114 A .4 shall comply with the requirements of Chapter 8 of TMS 402.
TABLE 2114A.4—GROSS CROSS-SECTIONAL AREA ALLOWABLE STRESS FOR DRY-STACK MASONRY Col2 DESCRIPTION MAXIMUM ALLOWABLE STRESS (psi) Compression 45 Flexural tension
Horizontal span
Vertical span30
18Shear 10 For SI: 1 pound per square inch = 0.006895 MPa. For SI: 1 pound per square inch = 0.006895 MPa. 2114 A .5 Construction. Construction of dry-stack masonry shall comply with ASTM C946.
21A-18 2025 CALIFORNIA BUILDING CODE
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CALIFORNIA BUILDING CODE – MATRIX ADOPTION TABLE
CHAPTER 22 – STEEL
(Matrix Adoption Tables are nonregulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)
CHBC § 1.0. High relevance — show source text
The report’s allowable values
shall be multiplied by a factor of three to obtain strength values and the strength reduction factor,φ, shall be taken equal to 1.0.|[BS] A108.2 Masonry shear strength. The unreinforced masonry shear strength, v mL, shall be determined for each masonry class from one of the following equations:
- When testing is performed in accordance with Section A106.2.3.1, the unreinforced masonry shear strength, v m, shall be determined by Equation A1-3.
Equation A1-3
v mL
= ----------------------------------------------0.75 0.75 v tL + P ---- A Dn - - 1.5
The mortar shear strength values, v tL, shall be determined in accordance with Section A106.2.3.6. 2. When alternate testing is performed in accordance with Section A106.2.3.3, unreinforced masonry shear, v mL, shall be determined by Equation A1-4.
Equation A1-4
v mL
0.75 f + P ---- D -
= ---------------------------------- sp A n - 1.5
[BS] A108.3 Masonry compression. Where any increase in wall dead plus live load compression stress occurs, the maximum compression stress in unreinforced masonry, Q G /A n, shall not exceed 300 pounds per square inch (2070 kPa).
[BS] A108.4 Masonry tension. Unreinforced masonry shall be assumed to have no tensile capacity.
[BS] A108.5 Wall tension anchors. The tension strength of wall anchors shall be the average of the tension test values for anchors having the same wall thickness and framing orientation.
[BS] A108.6 Foundations. For existing foundations, new total dead loads are permitted to be increased over the existing dead load by 25 percent. New total dead load plus live load plus seismic forces may be increased over the existing dead load plus live load by 50 percent. Higher values may be justified only in conjunction with a geotechnical investigation.
SECTION A109—ANALYSIS AND DESIGN PROCEDURE
[BS] A109.1 General. The elements of buildings hereby required to be analyzed are specified in Table A102.1.
[BS] A109.2 Selection of procedure. Buildings with rigid diaphragms shall be analyzed by the general procedure of Section A110. Buildings with flexible diaphragms shall be analyzed by the general procedure or, where applicable, are permitted to be analyzed by the special procedure of Section A111.
SECTION A110—GENERAL PROCEDURE
[BS] A110.1 Minimum design lateral forces. Buildings shall be analyzed to resist minimum lateral forces assumed to act nonconcurrently in the direction of each of the main axes of the structure in accordance with the following:
Equation A1-5
V = 0.75----------------------- S DS W - R
APPENDIX A-10 2025 CALIFORNIA EXISTING BUILDING CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
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.
- 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
When can I simply use 9 psi for an existing masonry wall?
You may use 9 psi ultimate shear for existing solid (non‑adobe) unreinforced masonry when a licensed architect/engineer certifies an inspection has been made, mortars joints are filled, bricks and mortar are reasonably good, and the unsupported height/length : thickness ≤ 13. § 8-805.1
Can the 9 psi be increased if mortar looks good?
Yes — 10 percent of axial direct stress due to wall weight may be added to the shear stress per § 8-805.1. For higher increases based on higher‑quality mortar, testing per CEBC Appendix A is required. § 8-805.1
Does this rule cover adobe or stone?
No — adobe is covered in § 8-806 (different allowances). Stone has separate subsections in CHBC § 8-805.2 and may require testing or anchors to be treated as solid masonry. § 8-805.1 / § 8-806 / § 8-805.2
What documentation does the enforcing agency expect?
A registered architect or structural engineer must provide the qualifying statement (inspection, filled joints, reasonable condition) and any test reports if higher strengths are claimed; CHBC § 8-802 requires the architect/engineer to assign allowable stresses and notes enforcing agency concurrence. § 8-805.1 / § 8-802
If I perform tests, which procedures apply?
The CHBC points to the California Existing Building Code Appendix A (CEBC Appendix A/Chapter A1) for in‑place shear, splitting tensile and other tests used to justify higher shear values. § 8-805.1 (reference to CEBC Appendix A)
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