Section A304 — STRENGTHENING REQUIREMENTS

[BS] A304.1 General.

[BS] A304.1.1 Scope. The structural weaknesses noted in Section A303 shall be strengthened in accordance with the requirements of this section. Strengthening work may include both new construction and alteration of existing construction. Except as provided herein, all strengthening work and materials shall comply with the applicable provisions of the California Building Code .

[BS] A304.1.2 Condition of existing wood materials. Existing wood materials that will be a part of the strengthening work (such as sills, studs and sheathing) shall be in a sound condition and free from defects that substantially reduce the capacity of the member. Any wood material found to contain fungus infection shall be removed and replaced with new material. Any wood material found to be infested with insects or to have been infested with insects shall be strengthened or replaced with new materials to provide a net dimension of sound wood equal to or greater than its undamaged original dimension.

[BS] A304.1.3 Floor joists not parallel to foundations. Floor joists framed perpendicular or at an angle to perimeter foundations shall be restrained either by an existing nominal 2-inch-wide (51 mm) continuous rim joist or by a nominal 2-inch-wide (51 mm) full-depth block between alternate joists in one- and two-story buildings, and between each joist in three-story buildings. Existing blocking for multiple-story buildings must occur at each joist space above a braced cripple wall panel.

Existing connections at the top and bottom edges of an existing rim joist or blocking need not be verified in one story buildings. In multiple-story buildings, the existing top edge connection need not be verified; however, the bottom edge connection to either the foundation sill plate or the top plate of a cripple wall shall be verified. The minimum existing bottom edge connection shall consist of 8d toenails spaced 6 inches (152 mm) apart for a continuous rim joist, or three 8d toenails per block. Where this minimum bottom edge-connection is not present or cannot be verified, a supplemental connection installed as shown in Figure A304.1.3 or A304.1.4(2) shall be provided. Where an existing continuous rim joist or the minimum existing blocking does not occur, new [3] / 4 -inch (19.1 mm) or [23] / 32 -inch (18 mm) wood structural panel blocking installed tightly between floor joists and nailed as shown in Figure A304.1.4(3) shall be provided at the inside face of the cripple wall. In lieu of wood structural panel blocking, tight fitting, full-depth 2-inch (51 mm) blocking may be used. New blocking may be omitted where it will interfere with vents or plumbing that penetrates the wall.

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APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

[BS] FIGURE A304.1.3—TYPICAL FLOOR TO CRIPPLE WALL CONNECTION (FLOOR JOISTS NOT PARALLEL TO FOUNDATIONS)

For SI: 1 inch = 25.4 mm, 1 pound = 4.4 N. NOTE: See manufacturing instructions for nail sizes associated with metal framing clips.

WHERE AN EXISTING RIM JOIST

NEW 2x SOLID BLOCKING INSTALLED

TO FIT TIGHTLY BETWEEN FLOOR

JOISTS

NEW FRAMING CLIP (FLAT) AT EACH BLOCK TO PLATE WITH A MINIMUM

HORIZONTAL CAPACITY OF 450

POUNDS. SPACE AS INDICATED ABOVE

[BS] A304.1.4 Floor joists parallel to foundations. Where existing floor joists are parallel to the perimeter foundations, the end joist shall be located over the foundation and, except for required ventilation openings, shall be continuous and in continuous contact with the foundation sill plate or the top plate of the cripple wall. Existing connections at the top and bottom edges of the end joist need not be verified in one-story buildings. In multiple-story buildings, the existing top edge connection of the end joist need not be verified; however, the bottom edge connection to either the foundation sill plate or the top plate of a cripple wall shall be verified. The minimum bottom edge connection shall be 8d toenails spaced 6 inches (152 mm) apart. If this minimum bottom edge connection is not present or cannot be verified, a supplemental connection installed as shown in Figure A304.1.4(1), A304.1.4(2) or A304.1.4(3) shall be provided.

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[BS] FIGURE A304.1.4(1)—TYPICAL FLOOR TO CRIPPLE WALL CONNECTION (FLOOR JOISTS PARALLEL TO FOUNDATIONS)

For SI: 1 inch = 25.4 mm, 1 pound = 4.4 N. NOTE: See manufacturing instructions for nail sizes associated with metal framing clips.

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APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

[BS] FIGURE A304.1.4(2)—TYPICAL FLOOR TO MUDSILL CONNECTIONS

THICK WOOD STRUCTURAL NEW 2x BLOCKING WITH 4-10d PANEL. SEE FIGURE A304.4.1(3) FOR NAILS EACH BLOCK TO SILL. PANEL AND NAILING LAYOUT PRE-DRILLED HOLES AS NEEDED

TO PRECLUDE SPLITTING

For SI: 1 inch = 25.4 mm.

NOTES:

1. See Section A304.3 for sill plate anchorage.

2. See manufacturing instructions for nail sizes associated with metal framing clips.

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APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

[BS] FIGURE A304.1.4(3)—ALTERNATIVE FLOOR FRAMING TO CRIPPLE WALL CONNECTION

EXISTING 2-2x OR 1-2x PLATE

NEW 2x BLOCK BETWEEN EACH

STUD WHEN EXISTING CRIPPLE

STUD WALL HAS SINGLE TOP PLATE.

NAIL TO TOP PLATE WITH 3-10d NAILS. (PRE-DRILL BLOCK)

WHERE AN EXISTING RIM JOIST OR BLOCKING

STRUCTURAL PANEL BLOCKING INSTALLED TO

BRACED PANELS, ALTERNATE JOIST SPACES AT OTHER LOCATIONS

1-STORY: ALTERNATE JOIST SPACE

"

SEE FIGURE A304.4.1(2) FOR BRACING

EXISTING RIM JOIST WITH

EXISTING NAILING TO BE

VERIFIED PER A304.1.4

For SI: 1 inch = 25.4 mm, 1 pound = 4.4 N. NOTE: See Section A304.4 for cripple wall bracing.

����������������������������������

NEW 2x BLOCKING. SEE REQUIREMENTS

WHERE EXISTING NAILING FROM EXISTING RIM

JOIST TO TOP PLATE CANNOT BE VERIFIED

PROVIDE NEW ¾ WOOD STRUCTURAL PANEL" BLOCKING. SEE REQUIREMENTS ABOVE.

�������������������������������

[BS] A304.2 Foundations.

[BS] A304.2.1 New perimeter foundations. New perimeter foundations shall be provided for structures with the structural weaknesses noted in Items 1 and 2 of Section A303. Soil investigations or geotechnical studies are not required for this work unless the building is located in a special study zone as designated by the code official or other authority having jurisdiction.

[BS] A304.2.2 Evaluation of existing foundations. Partial perimeter foundations or unreinforced masonry foundations shall be evaluated by a registered design professional for the force levels specified in Section A301.3. Test reports or other substantiating data to determine existing foundation material strengths shall be submitted to the code official. Where approved by the code official, these existing foundation systems shall be strengthened in accordance with the recommendations included with the evaluation in lieu of being replaced.

Exception: In lieu of testing existing foundations to determine material strengths, and where approved by the code official, a new nonperimeter foundation system designed for the forces specified in Section A301.3 shall be used to resist lateral forces from perimeter walls. A registered design professional shall confirm the ability of the existing diaphragm to transfer seismic forces to the new nonperimeter foundations.

[BS] A304.2.3 Details for new perimeter foundations. All new perimeter foundations shall be continuous and constructed according to Figure A304.2.3(1) and Table A304.2.3(1) or Figure A304.2.3(2) and Table A304.2.3(2). New construction materials

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APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

shall comply with the requirements of building code. Where approved by the code official, the existing clearance between existing floor joists or girders and existing grade below the floor need not comply with the building code.

Exception: Where designed by a registered design professional and approved by the code official, partial perimeter foundations shall be used in lieu of a continuous perimeter foundation.

[BS]TABLE A304.2.3(1)—NEW REINFORCED CONCRETE FOUNDATION SYSTEM

[BS] FIGURE A304.2.3(1)—NEW REINFORCED CONCRETE FOUNDATION SYSTEM

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.

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APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

[BS]TABLE A304.2.3(2)—NEW MASONRY CONCRETE FOUNDATION

[BS] FIGURE A304.2.3(2)—NEW MASONRY CONCRETE FOUNDATION

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.

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APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

[BS] A304.2.4 New concrete foundations. New concrete foundations shall have a minimum compressive strength of 2,500 pounds per square inch (17.24 MPa) at 28 days.

[BS] A304.2.5 New hollow-unit masonry foundations. New hollow-unit masonry foundations shall be solidly grouted. The grout shall have minimum compressive strength of 2,000 pounds per square inch (13.79 MPa). Mortar shall be Type M or S.

[BS] A304.2.6 New sill plates. Where new sill plates are used in conjunction with new foundations, they shall be minimum two times nominal thickness and shall be preservative-treated wood or naturally durable wood permitted by the building code for similar applications, and shall be marked or branded by an approved agency. Fasteners in contact with preservative-treated wood shall be hot-dip galvanized or other material permitted by the building code for similar applications. Anchors, that attach a preservative-treated sill plate to the foundation, shall be permitted to be of mechanically deposited zinc-coated steel with coating weights in accordance with ASTM B695, Class 55 minimum. Metal framing anchors in contact with preservative-treated wood shall be galvanized in accordance with ASTM A653 with a G185 coating.

[BS] A304.3 Foundation sill plate anchorage.

[BS] A304.3.1 Existing perimeter foundations. Where the building has an existing continuous perimeter foundation, all perimeter wall sill plates shall be anchored to the foundation with adhesive anchors or expansion anchors in accordance with Table A304.3.1.

Anchors shall be installed in accordance with Figure A304.3.1(1), with the plate washer installed between the nut and the sill plate. The nut shall be tightened to a snugtight condition after curing is complete for adhesive anchors and after expansion wedge engagement for expansion anchors. Anchors shall be installed in accordance with manufacturer’s recommendations. Expansion anchors shall not be used where the installation causes surface cracking of the foundation wall at the locations of the anchor.

Where existing conditions prevent anchor installations through the top of the sill plate, this connection shall be made in accordance with Figure A304.3.1(2), A304.3.1(3) or A304.3.1(4). Alternative anchorage methods having a minimum shear capacity of 900 pounds (4003 N) per connection parallel to the wall shall be permitted. The spacing of these alternative connections shall comply with the maximum spacing requirements of Table A304.3.1 for [1] / 2 -inch (12.7 mm) bolts.

e sill plate, this connection shall be made in accordance with Figure A304.3.1(2), A304.3.1(3) or A304.3.1(4). Alternative anchorage methods having a minimum shear capacity of 900 pounds (4003 N) per connection parallel to the wall shall be permitted. The spacing of these alternative connections shall comply with the maximum spacing requirements of Table A304.3.1 for [1] / 2 -inch (12.7 mm) bolts.

[BS] TABLE A304.3.1—SILL PLATE ANCHORAGE AND CRIPPLE WALL BRACING

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APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

[BS] FIGURE A304.3.1(1)—SILL PLATE ANCHORING TO EXISTING FOUNDATION [a, b]

For SI: 1 inch = 25.4 mm.

a. Plate washers shall comply with the following: 15 // 28 -inch anchor or bolt—3 inches × 3 inches × 0.229 inch minimum.-inch anchor or bolt—3 inches × 3 inches × 0.229 inch minimum. A diagonal slot in the plate washer is permitted in accordance with Table A304.3.1, Note b. b. See Figure A304.4.1(1) or A304.4.1(2) for cripple wall bracing.

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[BS] FIGURE A304.3.1(2)—ALTERNATIVE SILL PLATE ANCHORING IN EXISTING FOUNDATION—WITHOUT CRIPPLE WALLS AND FLOOR FRAMING NOT PARALLEL TO FOUNDATIONS [a, b]

EXISTING STUD WALL WITH SOLE

EXISTING 2x BLOCKING

OR RIM JOIST WITH

EXISTING TOENAILS

SEE SECTION A304.1.3

EXISTING SILL PLATE

EXISTING GROUND LEVEL

EXISTING SHEATHING OVER

EXISTING FLOOR FRAMING

7″ x [3] / 16 ″ x 9″ LONG PLATE WITH TWO [1] / 2 ″ DIAMETER ADHESIVE ANCHORS OR EXPANSION ANCHORS TO FOUNDATION WALL AND THREE [1] / 4 ″ DIAMETER LAG SCREWS PREDRILLED INTO SILL PLATE. PROVIDE SINGLE PIECE WOOD STRUCTURAL PANEL SHIM OR MULTIPLE LAYERS OF WOOD STRUCTURAL PANEL BETWEEN PLATE AND SILL WHEN SPACING EXCEEDS [3] / 16 ″ AND IS LESS THAN OR EQUAL TO 1 [1] / 2 ″. SEE TABLE A304.3.1 FOR SPACING OF ANCHORS

1″-5″ MIN.

1 / 4 ″ DIAMETER LAG SCREW 2 [1] / 2 ″ MIN. INTO SILL PLATE FOR SHIM ATTACHMENT

¾″

HOLE DIAMETER SHALL NOT EXCEED CONNECTOR DIAMETER BY MORE THAN [1] / 16 ″

SINGLE PIECE SHIM (AS REQUIRED)

5 / 16 ″ DIAMETER HOLES FOR [1] / 4 ″ LAG SCREWS

7″ x 9″ PLATE

For SI: 1 inch = 25.4 mm. a. If shim space exceeds 1 [1] / 2 inches, alternative details will be required. b. Where required, single piece shim shall be naturally durable wood or preservative-treated wood. If preservative-treated wood is used, it shall be isolated from the foundation system with a moisture barrier.

[BS] FIGURE A304.3.1(3)—ALTERNATIVE SILL PLATE ANCHOR TO EXISTING

FOUNDATION WITHOUT CRIPPLE WALL AND FLOOR FRAMING PARALLEL TO FOUNDATIONS

FOR SHIMS, WHERE REQUIRED SEE NOTE B, FIGURE A304.3.1(2)

SEE FIGURE A304.3.1(2) FOR

For SI: 1 inch = 25.4 mm.

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APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

[BS] FIGURE A304.3.1(4)—SILL PLATE ANCHORING TO EXISTING FOUNDATION—ALTERNATIVE CONNECTION FOR BATTERED FOOTING

For SI: 1 inch = 25.4 mm.

[BS] A304.3.2 Placement of anchors. Anchors shall be placed within 12 inches (305 mm), but not less than 9 inches (229 mm), from the ends of sill plates and shall be placed in the center of the stud space closest to the required spacing. New sill plates may be installed in pieces where necessary because of existing conditions. For lengths of sill plates 12 feet (3658 mm) or greater, anchors shall be spaced along the sill plate as specified in Table A304.3.1. For other lengths of sill plate, anchor placement shall be in accordance with Table A304.3.2.

Exception: Where physical obstructions such as fireplaces, plumbing or heating ducts interfere with the placement of an anchor, the anchor shall be placed as close to the obstruction as possible, but not less than 9 inches (229 mm) from the end of the plate. Center-to-center spacing of the anchors shall be reduced as necessary to provide the minimum total number of anchors required based on the full length of the wall. Center-to-center spacing shall be not less than 12 inches (305 mm).

[BS] TABLE A304.3.2—SILL PLATE ANCHORAGE FOR VARIOUS LENGTHS OF SILL PLATEa, b

[BS] A304.3.3 New perimeter foundations. Sill plates for new perimeter foundations shall be anchored in accordance with Table A304.3.1 and Figure A304.2.3(1) and Table A304.2.3(1) or Figure A304.2.3(2) and Table A304.2.3(2).

[BS] A304.4 Cripple wall bracing.

[BS] A304.4.1 General. Exterior cripple walls not exceeding 4 feet (1219 mm) in height shall be permitted to be specified by the prescriptive bracing method in Section A304.4. Cripple walls over 4 feet (1219 mm) in height require analysis by a registered design professional in accordance with Section A301.3.

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APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

[BS] FIGURE A304.4.1(1)—CRIPPLE WALL BRACING WITH NEW WOOD STRUCTURAL PANEL ON EXTERIOR FACE OF CRIPPLE STUDS

EXISTING 2x SILL PLATE. SEE FIGURES A304.3.1(1), A304.3.1(2), A304.3.1(3) OR A304.3.1(4) FOR

For SI: 1 inch = 25.4 mm.

NOTE: See Figure A304.3.1(1) for sill plate anchoring.

.1(3) FOR
EXISTING 2
FIGURES A
A304.3.1(3)
NEW CONN

[BS] FIGURE A304.4.1(2)—CRIPPLE WALL BRACING WITH WOOD STRUCTURAL PANEL ON INTERIOR FACE OF CRIPPLE STUDS

THICK WOOD STRUCTURAL NEW 2x BLOCKING WITH 4-10d PANEL. SEE FIGURE A304.4.1(3) FOR NAILS EACH BLOCK TO SILL. PANEL AND NAILING LAYOUT PRE-DRILLED HOLES AS NEEDED

TO PRECLUDE SPLITTING

For SI: 1 inch = 25.4 mm.

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APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

FIGURE A304.4.1(3) [BS] FIGURE A304.4.1(3)—PARTIAL CRIPPLE STUD WALL ELEVATION

2x BLOCKING FLAT ABOVE VENT OPENING.

2-IN.- TO 3-IN.-DIAMETER VENTILATION HOLES. SEE SECTION A304.4.3.

8d NAILS AT 4 IN. ON CENTER ON ALL EDGES OF EACH INDIVIDUAL PIECE

SILL BOLT

NEW 2x CRIPPLE STUD NAILED TO EXISTING STUD WITH 16d COMMON NAILS AT 6 IN. ON CENTER AT WOOD STRUCTURAL PANEL JOINT. 3 NAILS MIN.

GROUND LEVEL

EXISTING FOUNDATION WALL

1 [/ IN. MIN] 8 1 [/ IN. MIN] 8

VERTICAL SPLICE AT DOUBLE STUD VERTICAL SPLICE AT SINGLE STUD

For SI: 1 inch = 25.4 mm.

[BS] A304.4.1.1 Sheathing installation requirements. Wood structural panel sheathing shall be not less than [15] / 32 -inch (12 mm) thick and shall be installed in accordance with Figure A304.4.1(1) or A304.4.1(2). Individual pieces of wood structural panels shall be nailed with 8d common nails spaced 4 inches (102 mm) on center at all edges and 12 inches (305 mm) on center at each intermediate support with not less than two nails for each stud. Nails shall be driven so that their heads are flush with the surface of the sheathing and shall penetrate the supporting member not less than 1 [1] / 2 inches (38 mm). When a nail fractures the surface, it shall be left in place and not counted as part of the required nailing. A new 8d nail shall be located within 2 inches (51 mm) of the discounted nail and be hand-driven flush with the sheathing surface. Where the installation involves horizontal joints, those joints shall occur over nominal 2-inch by 4-inch (51 mm by 102 mm) blocking installed with the nominal 4-inch (102 mm) dimension against the face of the plywood. Vertical joints at adjoining pieces of wood structural panels shall be centered on studs such that there is a minimum [1] / 8 inch (3.2 mm) between the panels. Where required edge distances cannot be maintained because of the width of the existing stud, a new stud shall be added adjacent to the existing studs and connected in accordance with Figure A304.4.1(3).

[BS] A304.4.2 Distribution and amount of bracing. See Table A304.3.1 and Figure A304.4.2 for the distribution and amount of bracing required for each wall line. Each braced panel length must be not less than two times the height of the cripple stud. Where the minimum amount of bracing prescribed in Table A304.3.1 cannot be installed along any walls, the bracing must be designed in accordance with Section A301.3.

Exception: Where physical obstructions such as fireplaces, plumbing or heating ducts interfere with the placement of cripple wall bracing, the bracing shall then be placed as close to the obstruction as possible. The total amount of bracing required shall not be reduced because of obstructions.

APPENDIX A-40 2025 CALIFORNIA EXISTING BUILDING CODE

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APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

[BS] FIGURE A304.4.2—FLOOR PLAN-CRIPPLE WALL BRACING LAYOUT

[BS] FIGURE A304.4.2—FLOOR PLAN-CRIPPLE WALL BRACING LAYOUT nearly equal in spacing along the wall. Wherever possible,
panels should be laid out to begin and end on studs while
maintaining required panel lengths. This may require the
occasional addition of a new stud.
1.
2.
3.
REQUIRED BRACING FOR 1-STORY BUILDING
30 FT.
8 FT.
8 FT.
8 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
5 FT. 4 IN.
5 FT. 4 IN.
(4' EACH)
(4 FT. EACH)
40 FT.
REQUIRED BRACING FOR 2-STORY BUILDING
REQUIRED BRACING FOR 3-STORY BUILDING|2 FT.
8 IN.
2 FT.
8 IN.
NOTES:
Bracing shown assumes cripple stud height of 24 in.
Minimum panel length shall be two times the cripple stud
wall height.
All panels along a wall shall be nearly equal in length and
nearly equal in spacing along the wall. Wherever possible,
panels should be laid out to begin and end on studs while
maintaining required panel lengths. This may require the
occasional addition of a new stud.
1.
2.
3.
REQUIRED BRACING FOR 1-STORY BUILDING
30 FT.
8 FT.
8 FT.
8 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
5 FT. 4 IN.
5 FT. 4 IN.
(4' EACH)
(4 FT. EACH)
40 FT.
REQUIRED BRACING FOR 2-STORY BUILDING
REQUIRED BRACING FOR 3-STORY BUILDING|2 FT.
8 IN.
2 FT.
8 IN.
NOTES:
Bracing shown assumes cripple stud height of 24 in.
Minimum panel length shall be two times the cripple stud
wall height.
All panels along a wall shall be nearly equal in length and
nearly equal in spacing along the wall. Wherever possible,
panels should be laid out to begin and end on studs while
maintaining required panel lengths. This may require the
occasional addition of a new stud.
1.
2.
3.
REQUIRED BRACING FOR 1-STORY BUILDING
30 FT.
8 FT.
8 FT.
8 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
5 FT. 4 IN.
5 FT. 4 IN.
(4' EACH)
(4 FT. EACH)
40 FT.
REQUIRED BRACING FOR 2-STORY BUILDING
REQUIRED BRACING FOR 3-STORY BUILDING|2 FT.
8 IN.
2 FT.
8 IN.
NOTES:
Bracing shown assumes cripple stud height of 24 in.
Minimum panel length shall be two times the cripple stud
wall height.
All panels along a wall shall be nearly equal in length and
nearly equal in spacing along the wall. Wherever possible,
panels should be laid out to begin and end on studs while
maintaining required panel lengths. This may require the
occasional addition of a new stud.
1.
2.
3.
REQUIRED BRACING FOR 1-STORY BUILDING
30 FT.
8 FT.
8 FT.
8 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
5 FT. 4 IN.
5 FT. 4 IN.
(4' EACH)
(4 FT. EACH)
40 FT.
REQUIRED BRACING FOR 2-STORY BUILDING
REQUIRED BRACING FOR 3-STORY BUILDING|2 FT.
8 IN.
2 FT.
8 IN.
NOTES:
Bracing shown assumes cripple stud height of 24 in.
Minimum panel length shall be two times the cripple stud
wall height.
All panels along a wall shall be nearly equal in length and
nearly equal in spacing along the wall. Wherever possible,
panels should be laid out to begin and end on studs while
maintaining required panel lengths. This may require the
occasional addition of a new stud.
1.
2.
3.
REQUIRED BRACING FOR 1-STORY BUILDING
30 FT.
8 FT.
8 FT.
8 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
5 FT. 4 IN.
5 FT. 4 IN.
(4' EACH)
(4 FT. EACH)
40 FT.
REQUIRED BRACING FOR 2-STORY BUILDING
REQUIRED BRACING FOR 3-STORY BUILDING|2 FT.
8 IN.
2 FT.
8 IN.
NOTES:
Bracing shown assumes cripple stud height of 24 in.
Minimum panel length shall be two times the cripple stud
wall height.
All panels along a wall shall be nearly equal in length and
nearly equal in spacing along the wall. Wherever possible,
panels should be laid out to begin and end on studs while
maintaining required panel lengths. This may require the
occasional addition of a new stud.
1.
2.
3.
REQUIRED BRACING FOR 1-STORY BUILDING
30 FT.
8 FT.
8 FT.
8 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
5 FT. 4 IN.
5 FT. 4 IN.
(4' EACH)
(4 FT. EACH)
40 FT.
REQUIRED BRACING FOR 2-STORY BUILDING
REQUIRED BRACING FOR 3-STORY BUILDING|2 FT.
8 IN.
2 FT.
8 IN.
NOTES:
Bracing shown assumes cripple stud height of 24 in.
Minimum panel length shall be two times the cripple stud
wall height.
All panels along a wall shall be nearly equal in length and
nearly equal in spacing along the wall. Wherever possible,
panels should be laid out to begin and end on studs while
maintaining required panel lengths. This may require the
occasional addition of a new stud.
1.
2.
3.
REQUIRED BRACING FOR 1-STORY BUILDING
30 FT.
8 FT.
8 FT.
8 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
4 FT.
5 FT. 4 IN.
5 FT. 4 IN.
(4' EACH)
(4 FT. EACH)
40 FT.
REQUIRED BRACING FOR 2-STORY BUILDING
REQUIRED BRACING FOR 3-STORY BUILDING|

[BS] FIGURE A304.4.2—FLOOR PLAN-CRIPPLE WALL BRACING LAYOUT

[BS] FIGURE A304.4.2—FLOOR PLAN-CRIPPLE WALL BRACING LAYOUT

[BS] FIGURE A304.4.2—FLOOR PLAN-CRIPPLE WALL BRACING LAYOUT

[BS] FIGURE A304.4.2—FLOOR PLAN-CRIPPLE WALL BRACING LAYOUT

[BS] FIGURE A304.4.2—FLOOR PLAN-CRIPPLE WALL BRACING LAYOUT

[BS] FIGURE A304.4.2—FLOOR PLAN-CRIPPLE WALL BRACING LAYOUT

[BS] FIGURE A304.4.2—FLOOR PLAN-CRIPPLE WALL BRACING LAYOUT

[BS] FIGURE A304.4.2—FLOOR PLAN-CRIPPLE WALL BRACING LAYOUT

Bracing determination: ⎯ a 1-story building each end and not less than 40% of wall length. ⎯ Transverse wall ⎯ 30 ft. × 0.40 = 12 ft. minimum panel length = 4 ft. 0 in. a 2-story building each end and not less than 50% of wall length. ⎯ Longitudinal wall ⎯ 40 ft. × 0.50 = 20 ft. 0 in. minimum of bracing. a 3-story building each end and not less than 80% of wall length. Transverse wall ⎯ 30 ft. × 0.80 = 24 ft. 0 in. minimum of bracing. a. See Table 304.3.1 for buildings with both plaster walls and roofing exceeding 6 psf.

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 42.88 N/m [2] .

[BS] A304.4.3 Stud space ventilation. Where bracing materials are installed on the interior face of studs forming an enclosed space between the new bracing and the existing exterior finish, each braced stud space must be ventilated. Adequate ventilation and access for future inspection shall be provided by drilling one 2-inch to 3-inch-diameter (51 mm to 76 mm) round hole through the sheathing, nearly centered between each stud at the top and bottom of the cripple wall. Such holes should be spaced not less than 1 inch (25 mm) clear from the sill or top plates. In stud spaces containing sill bolts, the hole shall be located on the centerline of the sill bolt but not closer than 1 inch (25 mm) clear from the nailing edge of the sheathing. Where existing blocking occurs within the stud space, additional ventilation holes shall be placed above and below the blocking, or the existing block shall be removed and a new nominal 2-inch by 4-inch (51 mm by 102 mm) block shall be installed with the nominal 4-inch (102 mm) dimension against the face of the plywood. For stud heights less than 18 inches (457 mm), only one ventilation hole need be provided.

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

APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

[BS] A304.4.4 Existing underfloor ventilation. Existing underfloor ventilation shall not be reduced without providing equivalent new ventilation as close to the existing ventilation as possible. Braced panels may include underfloor ventilation openings where the height of the opening, measured from the top of the foundation wall to the top of the opening, does not exceed 25 percent of the height of the cripple stud wall; however, the length of the panel shall be increased a distance equal to the length of the opening or one stud space minimum. Where an opening exceeds 25 percent of the cripple wall height, braced panels shall not be located where the opening occurs. See Figure A304.4.1(3).

Exception: For homes with a post and pier foundation system where a new continuous perimeter foundation system is being installed, new ventilation shall be provided in accordance with the building code.

[BS] A304.5 Inspections . All work shall be subject to inspection by the code official including, but not limited to:

1. Placement and installation of new adhesive or expansion anchors installed in existing foundations. Special inspection may be required for adhesive anchors installed in existing foundations regulated by the prescriptive provisions of this chapter.
2. Installation and nailing of new cripple wall bracing.
3. Any work shall be subject to special inspection where required by the code official in accordance with the building code.

[BS] A304.5.1 Nails. All nails specified in this chapter shall be common wire nails of the following diameters and lengths:

1. 8d nails = 0.131 inch (3.3 mm) by 2 [1] / 2 inches (64 mm).
2. 10d nails = 0.148 inch (3.8 mm) by 3 inches (76 mm).
3. 12d nails = 0.148 inch (3.8 mm) by 3 [1] / 4 inches (83 mm).
4. 16d nails = 0.162 inch (4.1 mm) by 3 [1] / 2 inches (89 mm).

Nails used to attach metal framing connectors directly to wood members shall be as specified by the connector manufacturer in an approved report.

When approved by the Enforcing Agency, the strengthening work contained in this chapter may be completed in phases.

APPENDIX A-42 2025 CALIFORNIA EXISTING BUILDING CODE

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

CALIFORNIA EXISTING BUILDING CODE – MATRIX ADOPTION TABLE

APPENDIX A

CHAPTER A4 – EARTHQUAKE RISK REDUCTION IN WOOD-FRAME RESIDENTIAL BUILDINGS WITH SOFT, WEAK OR OPEN FRONT WALLS

(Matrix Adoption Tables are nonregulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

The state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.

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

APPENDIX A-44 2025 CALIFORNIA EXISTING BUILDING CODE

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

APPENDIX A—GUIDELINES FOR THE SEISMIC RETROFIT OF EXISTING BUILDINGS

CHAPTER A4

EARTHQUAKE RISK REDUCTION IN WOOD-FRAME RESIDENTIAL BUILDINGS WITH SOFT, WEAK OR OPEN FRONT WALLS