Skip to content

Appendix A — GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

Section A404 — PRESCRIPTIVE MEASURES FOR WEAK STORY

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] A404.1 Limitation. These prescriptive measures shall apply only to two-story buildings and only where deemed appropriate by the code official. These prescriptive measures rely on rotation of the second floor diaphragm to distribute the seismic load between the side and rear walls around a ground floor open area. In the absence of an existing floor diaphragm of wood structural panel or diagonal sheathing at the top of the first story, a new wood structural panel diaphragm of minimum thickness of [3] / 4 inch (19.1 mm) and with 10d common nails at 6 inches (152 mm) on center shall be applied.

[BS] A404.1.1 Additional conditions. To qualify for these prescriptive measures, the following additional conditions need to be satisfied by the retrofitted structure:

  1. Diaphragm aspect ratio L/W is less than 0.67, where W is the diaphragm dimension parallel to the soft, weak or openfront wall line and L is the distance in the orthogonal direction between that wall line and the rear wall of the ground floor open area.
  2. Minimum length of side shear walls = 20 feet (6096 mm).
  3. Minimum length of rear shear wall = three-fourths of the total rear wall length.
  4. Plan or vertical irregularities shall not be other than a soft, weak or open-front wall line.
  5. Roofing weight less than or equal to 5 pounds per square foot (240 N/m [2] ).
  6. Aspect ratio of the full second floor diaphragm meets the requirements of the building code for new construction.

[BS] A404.2 Minimum required retrofit.

[BS] A404.2.1 Anchor size and spacing. The anchor size and spacing shall be not less than [3] / 4 inch (19.1 mm) in diameter at 32 inches (813 mm) on center. Where existing anchors are inadequate, supplemental or alternative approved connectors (such as new steel plates bolted to the side of the foundation and nailed to the sill) shall be used.

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

APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

[BS] A404.2.2 Connection to floor above. Shear wall top plates shall be connected to blocking or rim joist at upper floor with not less than 18-gage galvanized steel angle clips 4 [1] / 2 inches (114 mm) long with 12-8d nails spaced not farther than 16 inches (406 mm) on center, or by equivalent shear transfer methods.

[BS] A404.2.3 Shear wall sheathing. The shear wall sheathing shall be not less than [15] / 32 -inch (11.9 mm), 5-ply Structural I with 10d nails at 4 inches (102 mm) on center at edges and 12 inches (305 mm) on center at field; blocked all edges with 3 by 4 board or larger. Where existing sill plates are less than 3-by thick, place flat 2-by on top of sill between studs, with flat 18-gage galvanized steel clips 4 [1] / 2 inches (114 mm) long with 12-8d nails or [3] / 8 -inch-diameter (9.5 mm) lags through blocking for shear transfer to sill plate. Stagger nailing from wall sheathing between existing sill and new blocking. Anchor new blocking to foundation as specified in this section.

l plates are less than 3-by thick, place flat 2-by on top of sill between studs, with flat 18-gage galvanized steel clips 4 [1] / 2 inches (114 mm) long with 12-8d nails or [3] / 8 -inch-diameter (9.5 mm) lags through blocking for shear transfer to sill plate. Stagger nailing from wall sheathing between existing sill and new blocking. Anchor new blocking to foundation as specified in this section.

[BS] A404.2.4 Shear wall hold-downs. Shear walls shall be provided with hold-down anchors at each end. Two hold-down anchors are required at intersecting corners. Hold-downs shall be approved connectors with a minimum [5] / 8 -inch-diameter (15.9 mm) threaded rod or other approved anchor with a minimum allowable load of 4,000 pounds (17.8 kN). Anchor embedment in concrete shall be not less than 5 inches (127 mm). Tie-rod systems shall be not less than [5] / 8 inch (15.9 mm) in diameter unless using high-strength cable. High-strength cable elongation shall not exceed [5] / 8 inch (15.9 mm) under a 4,000 pound (17.8 kN) axial load.

Get a plain-English answer with a citation back to this text.

Ask AI about this code
▸ 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…

GoCodebook provides public access, search, citation, multilingual explanation, and practical interpretation of legally adopted building regulations. It is not a substitute for the official ICC or California code publications.