Seismic retrofitting is the process of strengthening an existing building so it can better withstand earthquakes. Because most older buildings were designed and built before modern earthquake safety codes existed, they represent the greatest seismic risk in the country. Retrofitting addresses that gap by reinforcing a structure’s weak points, from its foundation connections to its walls and roof, so it’s less likely to collapse or sustain catastrophic damage during ground shaking.
Why Older Buildings Need Retrofitting
Modern building codes require specific structural features that help a building flex and absorb seismic energy without falling apart. But buildings constructed before these codes were adopted, many dating to the mid-20th century or earlier, simply weren’t designed with earthquakes in mind. Their foundations may not be anchored properly, their walls may lack bracing, and their connections between floors, walls, and roof may be too weak to hold together when the ground moves.
FEMA has identified the existing building stock as the principal source of seismic risk in the United States. Retrofitting these structures is significantly more expensive than building new earthquake-safe ones from scratch, but for millions of homes, schools, and commercial buildings already standing in seismic zones, it’s the only practical option.
How Wood-Frame Homes Are Retrofitted
For single-family houses, the most common retrofit targets the connection between the house and its concrete foundation. In many older wood-frame homes, the wooden frame simply sits on top of the foundation without being securely attached. During an earthquake, the house can slide right off. A “bolt-only” retrofit installs anchor bolts through the wooden sill plate (the bottom piece of the frame) into the foundation, locking the two together.
Many older homes also have short wood-framed walls between the foundation and the first floor, called cripple walls. These walls are often unbraced and tend to collapse sideways during shaking, which drops the house onto its foundation. Bracing them involves nailing structural plywood panels to the inside face of these walls, then anchoring the plywood to both the floor framing above and the foundation below. This combination of foundation bolting and cripple wall bracing is often called a “brace and bolt” retrofit, and it’s the most common type for residential properties in earthquake-prone areas like California.
Larger homes, hillside homes, and houses with basements or rooms built over garages face more complex challenges. A room over a garage, for example, creates what engineers call a “soft story” because the large opening weakens that level of the structure. These situations require additional reinforcement and can drive costs considerably higher.
Retrofitting Brick and Masonry Buildings
Unreinforced masonry (URM) buildings, typically older brick structures, are among the most dangerous in an earthquake. Brick walls are strong under compression but brittle under the lateral forces that earthquakes produce. They can crumble suddenly and with little warning.
Retrofitting these buildings works on two levels. At the structural level, engineers strengthen the building as a whole by tying its walls, floors, and roof together so they move as a unit rather than pulling apart. One common approach uses reinforced concrete overlays applied directly to the existing walls, essentially adding a new structural skin. Another method confines the building with steel tie sections that connect structural elements together. Research on school buildings in Iran found that the concrete overlay method was superior to steel ties in both effectiveness and cost.
At the element level, individual walls, columns, or connections can be strengthened on their own. Techniques include applying reinforced shotcrete (sprayed concrete) over walls, or using prestressed bars that actively compress masonry elements to increase their strength. The specific approach depends on how the building is deficient and what performance level the retrofit aims to achieve.
Performance Levels and Engineering Standards
Not every retrofit aims for the same outcome. The current U.S. engineering standard for evaluating and retrofitting existing buildings, known as ASCE 41-23, uses a performance-based approach. This means engineers first define what level of performance the building should achieve in a given earthquake, then design the retrofit to meet that target.
Performance levels range from preventing total collapse (the minimum goal) to keeping the building fully operational after a quake. The standard uses a three-tiered evaluation process. The first tier identifies potential deficiencies based on how similar buildings have performed in past earthquakes. Higher tiers involve progressively more detailed structural analysis. The 2023 update to this standard incorporated new seismic hazard data from the U.S. Geological Survey and added revised provisions for masonry buildings, concrete structures, and advanced analysis methods.
This performance-based framework is what allows engineers to tailor a retrofit to a building’s specific risks and the owner’s budget, rather than applying a one-size-fits-all solution.
What Retrofitting Costs
For a typical wood-frame home, costs vary widely depending on the home’s size, construction, and site conditions. A basic bolt-only retrofit, where the house just needs to be anchored to its foundation, runs about $3,000. A full brace-and-bolt retrofit, which adds cripple wall bracing, typically costs between $3,000 and $7,000.
Homes with soft-story conditions (like living space over a garage) are more expensive. Estimates for soft-story retrofits on single-family homes range from $15,000 to $28,000, and costs can climb significantly higher if the foundation itself needs modifications. There is no standard price for earthquake retrofitting because every home presents a different combination of age, design, soil conditions, and structural deficiencies.
Commercial buildings and larger structures cost proportionally more, especially unreinforced masonry buildings that may need extensive wall reinforcement or entirely new lateral force-resisting systems.
Grants and Financial Assistance
California’s Earthquake Brace + Bolt program offers eligible homeowners up to $3,000 toward a code-compliant seismic retrofit. To qualify, your home must be wood-framed, built before 1980, sitting on a raised foundation, and located in a designated ZIP code. The program also offers a supplemental grant for lower-income households (up to $72,080 in household income) that can cover up to 100% of the retrofit cost.
For homes with soft-story conditions, a separate grant program through the California Residential Mitigation Program offers up to $13,000. Other states and municipalities in seismic zones may have their own incentive programs, and some insurance companies offer premium discounts for retrofitted homes. If you’re in a high-risk area, checking with your state’s emergency management agency is the fastest way to find what’s available.