FEMA P-593 STEP-BY STEP PRESCRIPTIVE RETROFIT FOR CRIPPLE WALL BRACING & ANCHORAGE TO FOUNDATION

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1 INTRODUCTION Objective of provisions: The provisions of IEBC Appendix Chapter A3 are intended to reduce hazard of earthquake-induced damage (IEBC A301.1). These provisions are not intended to eliminate earthquake damage. This is partial seismic upgrade of vulnerable configuration. Alternative prescriptive provisions: Some local jurisdictions and regional groups have developed bolting and bracing provisions similar to the IEBC provisions, with modifications deemed appropriate for local use. The following information will be applicable in general concept, but may vary from local provisions in some details. Consult with building department regarding local revisions and resources. When this prescriptive design method should be used: 1) When undertaking voluntary seismic retrofit 2) When otherwise deemed appropriate by the building official. STEP 1: VERIFY IEBC SCOPE LIMITATIONS ARE MET (IEBC A301.2) (circle YES or NO) Building Configuration Scope YES NO One to four-family detached dwelling with crawlspace YES NO No lateral resistance is from poles or columns embedded in the ground YES NO Cripple walls do not exceed 4 ft in height (level and low-slope sites) YES NO 3 stories or less with no cripple walls, OR 3 stories or less with cripple walls less than 14 inches, OR 2 stories or less with cripple walls up to 4 ft high If all answers YES then proceed. If any of the above are NO, consult with building official or design professional regarding applicability of these provisions. Structural Weakness to be Retrofit YES NO 1. Sill plates or floor framing supported on ground without foundation system YES NO 2. Perimeter foundation system is isolated footings supporting posts and beams YES NO 3. Perimeter foundation system is not continuous YES NO 4. Perimeter foundation system is unreinforced masonry or stone YES NO 5. Foundation sill plates not connected or not adequately connected to foundation YES NO 6. Cripple walls not braced or not adequately braced If YES to one or more items above, proceed with those items. STEP 2 (RECOMMENDED): DRAW PLAN OF HOUSE AND CRAWL SPACE (Check each item when done) Identify location and extent of foundation Identify location of existing anchor bolts, if applicable Identify extent and location of cripple walls if applicable Indicate locations of cripple wall openings and interruptions including: ventilation and flood openings access openings fireplaces to the extent that they affect potential areas of access or work: o utility meters o plumbing o water heaters o HVAC equipment Indicate direction of floor framing Page 1 of 10

2 STEP 3: CONDUCT CONDITION SURVEY Identify whether any of the following conditions exist (circle YES or NO) REQUIRED CONDITION SURVEY YES NO Decay in members to be part of strengthening requires replacement of decayed framing (A ). Recommend replacement with decay-resistant material. YES NO Insect infestation in members to be part of strengthening requires strengthening or replacement of damaged framing (A ). YES NO Partial perimeter foundation requires evaluation by engineer or architect to determine if adequate for anticipated cripple wall loads (A ). YES NO Unreinforced masonry foundation requires evaluation by engineer or architect to determine 1) if adequate for anticipated cripple wall loads and 2) if anchorage to foundation will be adequate for anticipated cripple wall loads (A ). RECOMMENDED ADDITIONAL SURVEY ITEMS YES NO Signs of decay or water intrusion recommend that owner take steps to identify and repair water sources (leaking pipes, grading and drainage, etc) YES NO Anchor bolts rusted to the extent that their area is significantly reduced (i.e. loss of 25% of bolt area or more) recommend addition of replacement bolts YES NO Deteriorated existing foundation such that concrete or masonry mortar can be easily scrapped out with screw driver adhesive anchors may not hold well, consider 1) replace foundation, 2) add new foundation segments alongside existing or 3) cut out 1 by 1 keys in foundation and cast new concrete around new anchor bolts Page 2 of 10

3 STEP 4: DETERMINE NEW FOUNDATION REQUIREMENTS (IF APPLICABLE) (A304.2) New foundations are needed when: Structural weaknesses 1 and 2 are present (Step 1) Partial continuous foundations are found to not be adequate (Step 1, Weakness 3) Unreinforced masonry foundations are found to not be adequate (Step 1, Weakness 4) When otherwise determined appropriate New perimeter foundations are to be continuous and conform to Figure A3-1 or A3-2 and their table, or be designed by an engineer or architect. A geotechnical (soil) investigation may be required is the site is located in a special study zone. Check with building department. Figure A3-1 Figure A3-2 RECOMMEND: Indicating extent and detail for new foundation on retrofit plan (See Step 2). STEP 5: INDENTIFY FOUNDATION SILL PLATE ANCHOR SPACING (A304.3) All perimeter foundation sill plates are to be anchored to the foundation. Foundation sill plate anchor bolt spacing (or spacing of alternate connectors if applicable) needs to meet the requirements of Table A3-A: Page 3 of 10

4 Number of anchor bolts (or alternate connectors if applicable) per section of sill needs to meet requirements of Table A3-B: For sections of sill less than 30 inches one anchor bolt or alternate connection is required. Anchor bolts are to start between 9 and 12 inches from the end of the sill, and in the center of the stud bay closest to the required spacing. When the intended location is obstructed, place as close to the intended location as possible. RECOMMEND: Locating new anchor locations on retrofit plan (See Step 2). STEP 6: SELECT FOUNDATION SILL PLATE ANCHORAGE DETAILS (A304.3) Where cripple walls exist and height permits rotary hammer access, anchor bolts shall be per Figure A3-3. Where no cripple walls are present or height is inadequate, use of connectors per Figures A3-4A to A3-4C is permitted. Page 4 of 10

5 RECOMMEND: Identifying applicable detail at each perimeter wall on retrofit plan (See Step 2). STEP 7: VERIFY/ RETROFIT RIM JOIST, BLOCKING & CONNECTION (A & A ) Where floor joists are perpendicular to the foundation need to have: 1 & 2-story buildings: A continuous rim joist or full depth blocking in alternate joist bays 3-story buildings: A continuous rim joist of full depth blocking in every joist bay Where required rim joist or blocking does not exist, provide wood structural panel blocking in accordance with Figure A3-8. In 2 & 3 story buildings, the connection of the rim joist or blocking to the foundation sill plate or cripple wall top plate must be: Verified to be a minimum of 8d toenails at 6 in. for rim joist or 3-8d per block, or Retrofit with framing clip in accordance with Figure A3-8. Page 5 of 10

6 STEP 7 (CONTD): VERIFY/ RETROFIT RIM JOIST, BLOCKING & CONNECTION (A & A ) Where floor joists are parallel to the foundation need to have: End joist located over the foundation and in contact with the foundation sill plate or cripple wall top plates End joist continuous except for ventilation/ access openings Where required end joist is not adequately installed, provide wood structural panel blocking in accordance with Figure A3-9. In 2 & 3 story buildings, the connection of the end joist to the foundation sill plate or cripple wall top plate must be: Verified to be a minimum of 8d toenails at 6 in., or Retrofit with framing clip in accordance with Figure A3-9. Page 6 of 10

7 STEP 8: IDENTIFY DISTRIBUTION AND AMOUNT OF CRIPPLE WALL BRACING Amount of bracing needs to: Meet the requirements of Table A3-A, and Meet the requirements of Figure A3-10, and Have a bracing panel (plywood or OSB) width not less than two times the bracing panel height, and Where obstructions occur, the bracing shall be located as close to the intended location as possible; the total amount of bracing shall not be reduced. Where these requirements cannot be met, design by an engineer or architect is required. Page 7 of 10

8 STEP 9: SELECT DETAILS OF CRIPPLE WALL BRACING Cripple wall bracing detailing shall be: Conforming to Figures A3-5 (exterior sheathing) or A3-6 (interior sheathing) and A3-7 Plywood/ OSB sheathing, minimum 15/32 in thickness All vertical plywood/ OSB edges shall fall on existing studs and be installed with 1/8 in gap between sheathing panels or be installed on doubled studs in accordance with Figure S3-7 All other plywood/osb edges shall be blocked with 2x4 minimum blocking installed with 4-in face flat against sheathing Sheathing nailing shall be with 8d common nails, and penetrate 1-1/2 inches minimum into framing Sheathing nailing shall be at 4 in. on center at plywood/ OSB panel edges, 12 inches at other framing Sheathing nailing shall be driven flush with the sheathing surface, but not break the sheathing face. Where nail breaks the sheathing face, add another nail half way between existing nails and hand-drive flush. Page 8 of 10

9 STEP 10: VERIFY VENTILATION (A , A ), ACCESS AND FLOOD OPENINGS Cripple wall bracing, blocking, etc need to allow for ventilation, etc. as follows: Where sheathing is installed on inside face, stud bay ventilation is required per A See also Figure A3-7. Under floor ventilation shall be in accordance with A See also Figure A3-7. Flood vents, if required, are recommended to the in accordance with A Required access openings shall be maintained. STEP 11: QUALITY CONTROL (A304.5) Inspections: IEBC Section A304.5 lists minimum required inspections. OTHER NOTES Steps 1-11 address the primary steps identified in IEBC Appendix Chapter 3. Fee the chapter for additional details. References - This section is drawn primarily from IEBC provisions, FEMA G225 Seismic Retrofit Training, and ATC 48 Built to Resist Earthquakes. The ICC/SEAOC commentary to IEBC provides detailed explanations of Appendix Chapter A3 requirements, along with many applicable recommendations and cautions. Page 9 of 10

10 Example Plan with Typical Retrofit Design Information Page 10 of 10