Key Takeaways
- Seismic retrofitting strengthens existing buildings to better resist earthquake forces, focusing on the connections between your home's frame and its foundation.
- Three main retrofit types address different vulnerabilities: foundation bolting, cripple wall bracing, and soft-story retrofits — each targeting a specific structural weakness.
- Pre-1980 homes with raised foundations are the most common candidates, but mandatory retrofit programs in Los Angeles, San Francisco, and other California cities now require certain building types to comply.
- Costs range widely — from $3,000 for basic foundation bolting to $200,000+ for complex soft-story retrofits — but financial assistance programs like CEA Brace+Bolt, FEMA grants, and SBA disaster loans can significantly reduce out-of-pocket expenses.
- Retrofitting pays for itself by reducing potential earthquake damage, lowering insurance premiums, and increasing property value — making it one of the most cost-effective forms of disaster preparedness.
What Is Seismic Retrofitting?
Seismic retrofitting is the process of modifying an existing building to make it more resistant to earthquake ground motion. Unlike new construction — which must meet current seismic building codes — older homes were often built with little or no consideration for earthquake forces. Retrofitting bridges that gap by reinforcing the structural elements most likely to fail during shaking.
The concept is straightforward: earthquakes don't directly destroy most homes. Instead, the ground shaking causes specific structural connections to fail, which leads to the building shifting off its foundation, collapsing at weak points, or sustaining damage that makes it uninhabitable. Retrofitting targets those failure points before an earthquake exposes them.
In practical terms, most residential seismic retrofits focus on what happens between your home's wooden frame and its concrete foundation. This is where the vast majority of earthquake damage to single-family homes occurs. The wood-to-concrete connection, the short stud walls (called cripple walls) in the crawl space, and the lateral bracing that prevents your home from racking sideways during shaking are all common retrofit targets.
Seismic retrofitting is not about making your home "earthquake-proof" — no structure can fully withstand every possible earthquake. The goal is to keep your home on its foundation, prevent collapse, and make it safe to occupy after a seismic event. Engineers refer to this as achieving "life safety" performance, meaning the structure protects its occupants even if it sustains some damage.
Why Seismic Retrofitting Matters
The consequences of not retrofitting a vulnerable home can be severe. In the 1994 Northridge earthquake in Los Angeles, more than 24,000 housing units were rendered uninhabitable, and many of those were older wood-frame homes that slid off their foundations. Total damage exceeded $20 billion (approximately $44 billion in 2024 dollars), and a significant portion of that damage occurred in homes that could have been protected with relatively inexpensive retrofitting.
Beyond the immediate physical damage, unretrofitted homes create cascading financial problems. Standard homeowners insurance does not cover earthquake damage. Even if you carry earthquake insurance in California, the deductibles are typically 10–20% of the dwelling coverage, meaning you'll pay tens of thousands out of pocket before the policy kicks in. And if your home is a total loss due to a foundation failure that a $5,000 retrofit could have prevented, you're looking at rebuilding costs that could reach $300,000 or more.
There's also the displacement factor. After a major earthquake, homes that have shifted off their foundations are red-tagged — meaning no one can enter. You'll need temporary housing, and in a regional disaster, rental availability drops while prices spike. FEMA assistance, while helpful, is limited and slow. The average FEMA Individual Assistance grant after a presidentially declared disaster is modest and nowhere near enough to cover total rebuilding costs.
Retrofitting is essentially an insurance policy you pay once. The upfront cost is a fraction of what you'd pay to repair or rebuild after an earthquake, and the work is typically completed in one to three days for standard residential retrofits.
Types of Seismic Retrofitting
Foundation Bolting
Foundation bolting — also called anchor bolting or sill plate bolting — involves drilling through the wooden sill plate (the bottom piece of your home's wall framing) and into the concrete foundation below, then securing the connection with steel anchor bolts and nuts. In homes built before the 1950s, the sill plate often simply rests on the foundation by gravity, with no mechanical connection at all. Even homes built through the late 1970s may have insufficient or improperly spaced anchor bolts.
Without proper bolting, earthquake shaking can cause the entire house to slide laterally off its foundation. The house itself may remain intact, but it's now sitting on the ground next to its foundation — a total loss from a structural standpoint. Foundation bolting prevents this by creating a positive connection that transfers lateral forces from the house frame into the foundation.
The work typically involves installing expansion bolts or epoxy-set bolts every four to six feet along the sill plate, per current California Existing Building Code requirements. For most single-family homes, this costs between $3,000 and $7,000 and can be completed in one to two days.
Learn more about foundation bolting and cripple wall bracing →
Cripple Wall Bracing
Cripple walls are the short wood-framed walls that sit between the top of the concrete foundation and the bottom of the first floor in homes with raised foundations. These walls create the crawl space beneath the house, and they're typically only one to four feet tall. Despite their small size, they represent one of the most dangerous structural vulnerabilities in older California homes.
During an earthquake, unbraced cripple walls can collapse outward, dropping the first floor onto the foundation. This type of failure was widespread in the 1989 Loma Prieta earthquake, particularly in the Marina District of San Francisco, where dozens of homes with unbraced cripple walls suffered partial or complete collapse.
Cripple wall bracing involves installing structural plywood sheathing on the inside face of these short walls, along with proper nailing patterns and framing connections. The plywood acts as a shear wall, resisting the lateral forces that would otherwise cause the cripple wall to fold. The cost ranges from $3,000 to $8,000 depending on the home's perimeter and crawl space accessibility.
Most residential retrofits combine foundation bolting with cripple wall bracing, since both vulnerabilities are typically present in the same home. The combined cost for a bolt-and-brace retrofit is generally $5,000 to $10,000.
Soft-Story Retrofit
Soft-story buildings have a ground floor that is significantly weaker or more flexible than the floors above it. The classic example is an apartment building with parking or commercial space on the ground floor and residential units above. The open ground floor lacks the shear walls that the upper floors have, creating a "soft" story that can collapse during earthquake shaking while the upper floors remain relatively intact.
This type of failure is particularly dangerous because it causes "pancake" collapses where the upper floors drop directly onto the ground floor. The 1994 Northridge earthquake caused the collapse of multiple soft-story apartment buildings, leading directly to mandatory retrofit ordinances in Los Angeles and other California cities.
Soft-story retrofits are substantially more complex and expensive than bolt-and-brace work. They involve installing steel moment frames, steel braced frames, or reinforced plywood shear walls on the ground floor to match the stiffness and strength of the floors above. Engineering analysis is required to determine the specific retrofit approach, and the work must be designed by a licensed engineer and performed by a licensed contractor.
Costs for soft-story retrofits typically range from $50,000 to $200,000 or more depending on the building size, number of units, and the specific engineering requirements. For large multi-unit buildings, costs can reach $300,000 to $500,000 or higher.
Learn more about soft-story retrofits →
Comparison of Retrofit Types
| Retrofit Type | Description | Typical Cost Range | Applicable Buildings | Timeline |
|---|---|---|---|---|
| Foundation Bolting | Steel bolts connecting sill plate to concrete foundation | $3,000–$7,000 | Pre-1980 homes with raised foundations, missing or inadequate anchor bolts | 1–2 days |
| Cripple Wall Bracing | Structural plywood sheathing on short stud walls in crawl space | $3,000–$8,000 | Homes with raised foundations and unbraced cripple walls | 1–2 days |
| Bolt + Brace Combination | Foundation bolting plus cripple wall bracing together | $5,000–$10,000 | Pre-1980 raised-foundation homes (most common residential retrofit) | 1–3 days |
| Soft-Story Retrofit | Steel frames or shear walls added to weak ground floor | $50,000–$200,000+ | Multi-unit buildings with open ground floor (parking, commercial) | 2–6 months |
| Chimney Bracing | Steel bracing or rebuilding of unreinforced masonry chimney | $2,000–$10,000 | Homes with unreinforced brick or stone chimneys | 1–3 days |
| Hillside Home Bracing | Reinforcement of cripple walls and post-and-pier systems on slopes | $10,000–$40,000+ | Homes on hillsides with tall cripple walls or stilts | 1–4 weeks |
Who Needs Seismic Retrofitting?
Pre-1980 Construction
The most common candidates for seismic retrofitting are homes built before 1980. California's building codes have been updated significantly after each major earthquake — particularly after the 1933 Long Beach, 1971 San Fernando, and 1994 Northridge earthquakes — but homes built before these code updates don't retroactively comply with newer standards.
If your home was built before 1950, it almost certainly lacks proper foundation bolting and cripple wall bracing. Homes built between 1950 and 1979 may have some anchor bolts, but they often don't meet current spacing or installation requirements. After 1980, most California homes were built to codes that addressed these specific vulnerabilities, though some may still benefit from additional reinforcement.
Raised Foundation Homes
Homes with raised foundations (meaning there's a crawl space between the ground and the first floor) are the primary retrofit candidates. Slab-on-grade homes — where the concrete foundation is the floor — don't have cripple walls and already have a direct connection between the structure and the ground, making them less vulnerable to the specific failure modes that residential retrofitting addresses.
That said, slab-on-grade homes are not immune to earthquake damage. They can still suffer from soil liquefaction, lateral spreading, and damage to their above-grade structure. But the bolt-and-brace retrofits that form the backbone of residential seismic retrofitting programs are specifically designed for raised-foundation homes.
Hillside Homes
Homes built on hillsides often have tall cripple walls or post-and-pier foundations on the downhill side. These tall, slender structural elements are particularly vulnerable to earthquake shaking because they amplify ground motion and have less resistance to lateral forces. A home with a 10-foot cripple wall on the downhill side is far more vulnerable than an identical home on flat ground with a 2-foot cripple wall.
Hillside homes typically require more extensive (and expensive) retrofitting than flat-ground homes. The work may include steel bracing, moment frames, or engineered shear wall systems, and the costs can range from $10,000 to $40,000 or more.
Multi-Unit Soft-Story Buildings
Apartment buildings and condominiums with soft ground floors are mandatory retrofit targets in several California cities. These buildings house multiple families, and their collapse potential during an earthquake represents both a life-safety hazard and a major housing displacement risk.
California's Mandatory Retrofit Programs
Several California cities have enacted mandatory seismic retrofit ordinances targeting the most vulnerable building types.
Los Angeles
Los Angeles passed its mandatory soft-story retrofit ordinance (Ordinance 183893) in 2015, following the 2014 ShakeOut scenario report that identified soft-story buildings as the single greatest risk to housing stock in a major earthquake. The ordinance requires owners of approximately 13,500 wood-frame soft-story buildings to complete seismic retrofits. The city has phased compliance deadlines, and owners who fail to comply face penalties and potential loss of certificate of occupancy.
LA's program also includes provisions for non-ductile concrete buildings, which are even more dangerous than soft-story wood-frame buildings but significantly more expensive to retrofit.
San Francisco
San Francisco's Mandatory Seismic Retrofit Program, established under Ordinance 66-13, requires owners of wood-frame soft-story buildings with five or more units to complete seismic retrofits. The program covers approximately 4,900 buildings and has tiered compliance deadlines based on building size and occupancy. The city's Department of Building Inspection maintains a public database of building compliance status.
San Francisco also has specific requirements for unreinforced masonry buildings (URM) under the Community Action Plan for Seismic Safety (CAPSS).
Other California Cities
Several other California cities have adopted or are developing mandatory retrofit programs, including Berkeley, Oakland, Pasadena, Santa Monica, West Hollywood, and Beverly Hills. Each program has its own scope, deadlines, and specific requirements. If you own a multi-unit building in a California city, check with your local building department to determine whether your property is subject to mandatory retrofit requirements.
How to Start a Seismic Retrofit
Step 1: Determine Your Home's Vulnerability
Start by answering a few basic questions: When was your home built? Does it have a raised foundation with a crawl space? Are there cripple walls visible in the crawl space? Can you see anchor bolts along the sill plate? Is the home on a hillside?
If your home was built before 1980 and has a raised foundation, it's a strong candidate for a bolt-and-brace retrofit. You can get a preliminary assessment by looking in your crawl space (if accessible) for visible anchor bolts and plywood sheathing on the cripple walls. If you see neither, your home almost certainly needs retrofitting.
The CEA Brace+Bolt program website has a tool for checking whether your home's ZIP code is in an eligible area and provides resources for understanding your home's specific vulnerabilities.
Step 2: Find a Licensed Contractor
For most residential retrofits, you'll need a licensed contractor. In California, seismic retrofit work must be performed by a contractor with a B (General Building), C-8 (Concrete), or A (General Engineering) license, depending on the scope of work.
The CEA Brace+Bolt contractor list is a good starting point, as these contractors have been specifically vetted for residential seismic retrofit work. You can also search for licensed contractors through the California Contractors State License Board (CSLB) at www.cslb.ca.gov.
Get at least three bids. Seismic retrofit pricing varies significantly between contractors, and you want to compare both price and scope of work. Make sure each bid specifies the number and type of anchor bolts, the linear footage of cripple wall bracing, and the specific materials to be used.
Step 3: Obtain Permits
Seismic retrofit work requires a building permit in most California jurisdictions. The permit process ensures that the work meets current code requirements and that it will be inspected upon completion.
For standard bolt-and-brace retrofits that follow the California Existing Building Code's prescriptive standard plans (identified as Plans A, B, and C — corresponding to foundation-only bolting, cripple wall bracing, and combination work), the permit process is typically straightforward and can often be obtained over the counter.
More complex retrofits — including soft-story work, hillside homes, and any project that doesn't fit the standard plans — will require engineered plans prepared by a licensed engineer, which adds both time and cost to the process.
Step 4: Complete the Work and Final Inspection
Once your contractor completes the retrofit, your local building department will send an inspector to verify that the work was done correctly. The inspector will check bolt spacing, plywood nailing patterns, hardware connections, and other details against the approved plans.
After passing inspection, you'll receive a final sign-off on your permit. Keep this documentation — it's proof that your home has been retrofitted, which is valuable for insurance purposes, property value, and future real estate transactions.
Cost Overview and Financial Assistance
The cost of seismic retrofitting varies dramatically based on the type of work, the size and configuration of your home, and local labor rates. Here's what to expect:
See our detailed guide to earthquake retrofitting costs →
Financial Assistance Programs
CEA Brace+Bolt Program
The California Earthquake Authority's (CEA) Brace+Bolt program offers grants of up to $3,000 toward the cost of a standard bolt-and-brace retrofit for eligible homeowners. The program targets homes in high-seismic-risk ZIP codes across California. Registration opens annually, and slots are limited, so homeowners should register early. Since 2014, the program has helped over 20,000 homeowners retrofit their homes.
FEMA Hazard Mitigation Grant Program (HMGP)
After a presidentially declared disaster, FEMA's Hazard Mitigation Grant Program provides funding to state and local governments for projects that reduce future disaster losses. Residential seismic retrofitting is an eligible activity, though funding flows through state agencies and availability depends on declared disasters in your area.
FEMA Building Resilient Infrastructure and Communities (BRIC)
The BRIC program provides annual pre-disaster mitigation funding, unlike HMGP which requires a disaster declaration. States and local governments apply on behalf of communities, and residential retrofit projects can be included in applications. The program has funded hundreds of millions in mitigation projects since its inception in 2020.
SBA Disaster Loans
The U.S. Small Business Administration offers low-interest disaster loans that can include funding for mitigation measures, including seismic retrofitting, for both homeowners and businesses. These loans are available after a presidentially declared disaster and offer favorable interest rates and repayment terms.
State and Local Programs
Some California cities offer additional financial incentives for seismic retrofitting. Los Angeles, for example, has offered property tax exclusions for seismic retrofit improvements under California Revenue and Taxation Code Section 74. Check with your local building department or tax assessor's office for programs specific to your area.
Table: Financial Assistance Summary
| Program | Funding Amount | Eligibility | How to Apply |
|---|---|---|---|
| CEA Brace+Bolt | Up to $3,000 grant | Homeowners in eligible CA ZIP codes; pre-1980 raised-foundation homes | Register at earthquakebracebolt.com during open enrollment |
| FEMA HMGP | Varies (75% federal / 25% local match) | Post-disaster; through state/local governments | Through your state emergency management agency |
| FEMA BRIC | Varies (75% federal / 25% local match) | Pre-disaster; through state/local governments | Through your state emergency management agency |
| SBA Disaster Loans | Up to $500,000 (homeowners) | Post-disaster declaration | Apply through SBA.gov or at Disaster Recovery Centers |
| CA Property Tax Exclusion | Value of retrofit excluded from reassessment | Active seismic retrofit improvements in CA | File with county assessor within 6 months of completion |
Seismic Retrofitting Beyond California
While California has the most developed residential retrofit programs in the United States, seismic risk exists across the country. The Pacific Northwest (Oregon and Washington), the New Madrid Seismic Zone in the central U.S., and portions of the Intermountain West all face significant earthquake hazards.
Oregon passed Senate Bill 3 in 2023, creating a seismic retrofit grant program for homes and schools. Washington state has funded school seismic retrofits through its capital budget. And the USGS National Seismic Hazard Maps identify areas of elevated risk throughout the United States that many homeowners don't realize they're in.
If you live outside California and want to assess your seismic risk, the USGS Earthquake Hazard Program provides hazard maps and information at earthquake.usgs.gov. While residential retrofit programs are less common outside California, the same engineering principles apply, and earthquake-resistant building techniques are relevant anywhere earthquakes can occur.
Sources
- California Existing Building Code, 2022 Edition — International Code Council. Available at: https://codes.iccsafe.org/content/CEBC2022P6
- California Earthquake Authority — Brace+Bolt Program. Available at: https://www.earthquakebracebolt.com
- FEMA Hazard Mitigation Grant Program (HMGP). Available at: https://www.fema.gov/grants/mitigation/hazard-mitigation
- FEMA Building Resilient Infrastructure and Communities (BRIC). Available at: https://www.fema.gov/grants/mitigation/building-resilient-infrastructure-communities
- City of Los Angeles — Ordinance 183893, Mandatory Earthquake Hazard Reduction in Existing Wood-Frame Buildings with Soft, Weak, or Open-Front Walls.
- San Francisco Department of Building Inspection — Mandatory Seismic Retrofit Program, Ordinance 66-13.
- USGS Earthquake Hazards Program — National Seismic Hazard Maps. Available at: https://earthquake.usgs.gov
- Applied Technology Council — FEMA P-1100, Vulnerability-Based Seismic Assessment and Retrofit of One- and Two-Family Dwellings, 2019.
- California Revenue and Taxation Code, Section 74 — Active Solar Energy System / Seismic Retrofit Exclusion.
- USGS — The 1994 Northridge Earthquake: Lessons Learned. Available at: https://earthquake.usgs.gov