Brace + Bolt – Seismic Retrofit
Surrounding the crawl space under the ﬁrst ﬂoor, many houses have a short wood framed wall (“cripple wall”) that needs to be strengthened to help prevent the house from sliding or toppling off of its foundation during an earthquake. Seismic Retrofitting involves:
- Bolting: Adding anchor bolts in the crawl space to improve the connection between the wood framing of a building and its concrete foundation.
- Bracing: Adding plywood to the cripple walls to help keep the house from toppling off of the foundation during an earthquake.
An Earthquake Brace + Bolt (EBB) retrofit is in compliance with California Building Code Chapter A3. Chapter A3 is specific to light, wood-frame houses. This is why it is important to make sure your house has a foundation that is in compliance. Qualifying foundations are concrete and reinforced masonry and include cripple walls or stem walls.
Chapter A3 allows:
- a prescriptive plan for houses that sit directly on their foundation (BOLT-ONLY RETROFIT);
- a prescriptive plan for houses with cripple walls 4 feet tall or less (BRACE AND BOLT RETROFIT); and,
- an engineered solution for cripple walls that exceed 4 feet tall up to 7 feet tall (ENGINEERED SOLUTION).
All retrofit work that complies with Chapter A3 is done in the crawl space and around the perimeter of the foundation. The approved retrofit is for bolting (stem wall only) or bolting and bracing (cripple wall)–anchor bolts or foundation plates and plywood or OSB sheathing on the perimeter cripple walls.
- Bolting=anchor bolts or foundation plates
- Bracing= plywood or OSB sheathing
- An engineered solution is unique to each house
Houses with a slab on grade foundation, unreinforced masonry or stone foundation do not qualify for this type of retrofit.
EBB also requires properly strapping the water heater. During past earthquakes, water heaters have moved or tipped over if they were not securely anchored to adjacent walls or floors. This movement has resulted in gas line or water line leaks, and electrical wiring damage. Gas line leaks and damaged electrical wiring pose health and fire hazards, and water line leaks can cause significant and costly property damage.
EBB was created to provide incentives to California homeowners to seismically retrofit wood-frame residential structures. As an accommodation to individuals that may have some need to have a third-party representative complete the EBB Program Application, we provide the Registration Authorization Form.
The seismic retrofit includes adding anchor bolts and bracing in the crawl space around the perimeter of the foundation to improve the connection between the wooden framing and concrete foundation. Contractors experienced in seismic retrofitting, specifically with California Existing Building Code (CEBC) Chapter A3, 2010 Edition, are sought after for this work.
For more information or to schedule a free estimate, give us a call today at (408) 785-1343