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Appendix A — GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

Section A108 — DESIGN STRENGTHS

2025 California Existing Building Code (Title 24, Part 10) · 2025 edition · updated 2026-07-27 · California

Italicized text is a California amendment to the model code, as printed in the official publication.

[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

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. 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.

[BS] TABLE A108.1(2)—STRENGTH VALUES OF NEW MATERIALS USED IN CONJUNCTION WITH EXISTING CONSTRUCTION

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—3,600 lbs. per anchor.
Shear—same as for shear anchors.

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

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. Bolt spacing shall not exceed 6 feet on center and shall be not less than 12 inches on center.
f. An alternative adhesive anchor bolt system is permitted to be used providing: its properties and installation conform to an ICC Evaluation Service Report; and the report
states that the system’s use is in unreinforced masonry as an acceptable alternative to Sections A107.4 and A113.1 or TMS 402, Section 2.1.4. 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:

  1. 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.

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▸ Contents — 2025 California Existing Building Code (Title 24, Part 10)
2025 California Existing Building Code (Title 24, Part 10)
  1. 104.11 for consideration of alternative means of compliance.
  2. Chapter 1 — ADMINISTRATION
  3. Chapter 2 — DEFINITIONS
  4. Chapter 3 — PROVISIONS FOR ALL COMPLIANCE METHODS
  5. Chapter 3A — PROVISIONS FOR ALL COMPLIANCE METHODS
  6. Chapter 4 — REPAIRS
  7. Chapter 4A — REPAIRS
  8. Chapter 5 — PRESCRIPTIVE COMPLIANCE METHOD
  9. Chapter 5A — PRESCRIPTIVE COMPLIANCE METHOD
  10. Chapter 6 — CLASSIFICATION OF WORK
  11. Chapter 7 — ALTERATIONS—LEVEL 1
  12. Chapter 8 — ALTERATIONS—LEVEL 2
  13. Chapter 9 — ALTERATIONS—LEVEL 3
  14. Chapter 10 — CHANGE OF OCCUPANCY
  15. Chapter 11 — ADDITIONS
  16. Chapter 12 — HISTORIC BUILDINGS
  17. Chapter 13 — PERFORMANCE COMPLIANCE METHODS
  18. Chapter 14 — RELOCATED OR MOVED BUILDINGS
  19. Chapter 15 — CONSTRUCTION SAFEGUARDS
  20. Chapter 16 — REFERENCED STANDARDS
  21. ▸ Appendix A — GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING B…
    Overview
    1. Section A100 — APPLICATION
    2. Section A101 — PURPOSE
    3. Section A102 — SCOPE
    4. Section A103 — DEFINITIONS
    5. Section A104 — SYMBOLS AND NOTATIONS
    6. Section A105 — GENERAL REQUIREMENTS
    7. Section A106 — MATERIALS REQUIREMENTS
    8. Section A107 — QUALITY CONTROL
    9. Section A108 — DESIGN STRENGTHS
    10. Section A109 — ANALYSIS AND DESIGN PROCEDURE
    11. Section A110 — GENERAL PROCEDURE
    12. Section A111 — SPECIAL PROCEDURE
    13. Section A112 — ANALYSIS AND DESIGN
    14. Section A113 — DETAILED BUILDING SYSTEM DESIGN REQUIREMENTS
    15. Section A114 — WALLS OF UNBURNED CLAY, ADOBE OR STONE MASONRY
    16. Section A201 — PURPOSE
    17. Section A202 — SCOPE
    18. Section A203 — DEFINITIONS
    19. Section A204 — SYMBOLS AND NOTATIONS
    20. Section A205 — GENERAL REQUIREMENTS
    21. Section A206 — ANALYSIS AND DESIGN
    22. Section A207 — MATERIALS OF CONSTRUCTION
    23. Section A301 — GENERAL
    24. Section A302 — DEFINITIONS
    25. Section A303 — STRUCTURAL WEAKNESSES
    26. Section A304 — STRENGTHENING REQUIREMENTS
    27. Section A401 — GENERAL
    28. Section A402 — DEFINITIONS
    29. Section A403 — ANALYSIS AND DESIGN
    30. Section A404 — PRESCRIPTIVE MEASURES FOR WEAK STORY
    31. Section A405 — MATERIALS OF CONSTRUCTION
    32. Section A406 — CONSTRUCTION DOCUMENTS
    33. Section A407 — QUALITY CONTROL
    34. Section A501 — REFERENCED STANDARDS
  22. Appendix B — SUPPLEMENTARY ACCESSIBILITY REQUIREMENTS FOR EXIS…
  23. Appendix C — GUIDELINES FOR THE WIND RETROFIT OF EXISTING BUIL…
  24. Appendix D — BOARD OF APPEALS
  25. Appendix E — TEMPORARY EMERGENCY USES
  26. Appendix A — GUIDELINES ON FIRE RATINGS OF ARCHAIC MATERIALS A…

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