Earthquake-resistant homes: what works in California, the Northwest, New Madrid and Charleston

# Earthquake-resistant homes

Direct answer. The safest house in an earthquake is the one that weighs the least, bends the most without breaking, and is tied together from roof to foundation. That is why a properly braced light wood-frame house, the most common house in America, has the best life-safety record of any residential type, and why heavy, stiff, unreinforced walls have the worst. Concrete, ICF, SCIP and steel can all be made earthquake-resistant, but they get there through engineering, ductile reinforcement and connections, not through mass. This page is the hub; it links to the systems and the regions.

If you came here from a hurricane page: the two hazards pull in opposite directions on one variable, weight. Everything else they ask for, a continuous load path and good connections, is the same.

Where the hazard is

The U.S. Geological Survey's National Seismic Hazard Model is the basis for the seismic design maps in the building code. The 2023 model, the first to cover all 50 states at once, found that nearly 75% of the country could experience potentially damaging shaking, identified nearly 500 additional faults, and noted that 37 states have had a magnitude 5 or larger earthquake in the last 200 years. The hazard is highest on the West Coast, in Alaska and Hawaii, and in the Intermountain West, but it is not confined there.

The building code translates the map into a Seismic Design Category (SDC A through E) for your site, based on expected ground motion and soil class. The SDC, not the state, decides what your house must do. Ask your building department for yours; it is public.

Why light often beats heavy

An earthquake does not push on a house the way wind does. The ground moves and the house's own weight, trying to stay put, generates the force: force equals mass times acceleration. Double the weight, double the force. That single relation explains most of what follows.

• Light wood frame. Low mass, so low force; plywood or OSB shear walls and nailed connections deform and absorb energy without snapping. The FEMA-funded CUREE-Caltech Woodframe Project after Northridge (1994) was the first systematic study of as-built houses and confirmed that correctly proportioned light-frame houses get damaged but do not readily collapse. FEMA 232, the homebuilders' guide updated in September 2024, is written for this house. Its failure modes are specific and fixable: unbolted sills, unbraced cripple walls, soft stories over garages, heavy masonry chimneys.
• Cold-formed steel frame. Behaves like wood frame seismically: light and ductile, with screwed or welded diagonal bracing or sheathing.
• Reinforced concrete and ICF. Heavy, so high force, but reinforced concrete shear walls are very strong and, when detailed with ductile reinforcement, perform well. Independent testing of ICF walls (Portland State, 2019; 16WCEE, 2017; ASCE 2009) shows performance governed by the reinforcement layout and concrete, not by the form system, and that screen-grid and flat-wall ICF behave differently. ICF has no codified seismic performance factors of its own in U.S. standards; it is designed as reinforced concrete.
• SCIP. A thin-shell sandwich with relatively low mass for a concrete system and good in-plane stiffness; shake-table tests abroad (Mashal et al., PCI Journal 2022) show strong performance. In the U.S. it is an engineered system permitted under a product-specific evaluation report.
• Reinforced masonry. Acceptable when fully grouted and reinforced to code; a large step up from unreinforced.
• Unreinforced masonry (URM) and adobe. The worst performers in every U.S. earthquake on record. Heavy, brittle, no ductility. Many western cities require or incentivize URM retrofits.

The code encodes this. The International Residential Code's prescriptive bracing tables are calibrated for light-frame walls; FEMA 232 notes that if concrete or masonry walls are mixed with light-frame walls in any story above grade, an engineered design is required, because the heavy elements raise the earthquake load beyond what the prescriptive bracing can handle. Fireplaces, chimneys and veneer are the only masonry the prescriptive path tolerates, and they are still the elements that fail first.

What every earthquake-resistant house has

1. A continuous load path. Roof to walls to floors to foundation, with hold-downs at shear wall ends and anchor bolts in the sill.
2. Enough bracing, well distributed. Shear walls or braced panels in both directions, on every story, without large unbraced openings on one side.
3. No soft story. A garage or open ground floor under a heavy upper floor is the most common collapse geometry; it needs a moment frame or added shear walls.
4. Regular shape and even mass. FEMA 232 emphasizes that an offset between the center of mass and the center of resistance, from an L-shaped plan or a masonry chimney at one end, twists the house.
5. Light roof and light finishes. Tile roofs, stone veneer and thick stucco add mass at the worst height.
6. Anchored contents. Water heater, tall furniture, gas shutoff.

Retrofitting an existing house, and who pays

For the typical raised-foundation wood house, the highest-value retrofit is a seismic bolt-and-brace: anchor the sill plate to the foundation and sheathe the cripple walls with plywood or OSB, done to California Existing Building Code Chapter A3 or the local equivalent. The California Residential Mitigation Program puts a contractor-installed job at $3,000 to $7,000, less if you do it yourself.

California funds it. Earthquake Brace + Bolt (EBB), run by CRMP with money from the California Earthquake Authority and FEMA's Hazard Mitigation Grant Program, pays up to $3,000 toward a code-compliant retrofit of a pre-1980 wood-frame house on a raised foundation, plus a supplemental grant of up to $7,000 (which can cover 100% of the job) for households earning $94,480 or less. Registration opens for a limited window each year across more than 1,100 high-hazard ZIP codes; the program operator reports well over 20,000 retrofits funded since it began. A separate CEA Brace + Bolt program has offered the same $3,000 to invited CEA policyholders. Once the work is verified, the CEA's Hazard Reduction Discount cuts the earthquake premium by up to 25% (tiered by house age and foundation type: 20–25% for raised-foundation homes, 10–15% for others).

For a house with living space over a garage, a soft-story retrofit (FEMA P-1100; CRMP's Earthquake Soft-Story program). For URM, wall anchors, parapet bracing and sometimes new shear walls. For heavy roofs, lighter coverings. None of these change the house's material; they change its connections.

Sheathing

Seismic bracing in frame houses is sheathing: wood structural panels nailed at close spacing are the standard, and their fastener schedule is where the ductility comes from. Alternatives exist. Magnesium oxide (MgO) board is marketed as a non-combustible structural sheathing; it is rated for that use in some evaluation reports, but the independent record on moisture behavior is mixed (chloride-based boards failed widely in Denmark, per DTU, and have been flagged by Canadian and UK bodies), and the IIBEC review of MgO sheathing notes that fasteners must engage framing, not just the board. For seismic use, a sheathing's tested fastener performance under cyclic load is what matters; ask for that data from a third party before substituting it for plywood or OSB.

Where hurricane and earthquake meet

Charleston and the lower Mississippi Valley have to design for both. Wind design wants mass and stiffness; seismic design wants lightness and ductility. In practice the resolution is the same thing both codes already demand: a continuous load path with engineered connections. A light, well-strapped roof on reinforced walls; impact openings that are also well anchored; a foundation that resists uplift and lateral load. Heavy systems are fine when engineered for the local SDC; light systems are fine when strapped for the local wind speed. The error is picking a material for one hazard and forgetting the other.

Insurance

Earthquake coverage is a separate policy or endorsement nearly everywhere, and wall material matters more here than in wind: Consumers' Checkbook notes earthquake premiums are substantially higher for masonry houses than for frame. In California, the CEA's retrofit discount of up to 25% is the clearest example of mitigation paying back on the premium side; retrofitting usually pays back through avoided loss as well.

System pages in this hub

• Light wood frame · Cold-formed steel · ICF · SCIP · Reinforced masonry · Mass timber
• Regional notes: California · Pacific Northwest · New Madrid · South Carolina

Building in a seismic design category C, D or E? BuiltStrong's advisory checks your site's SDC and soil, weighs it against your other hazards, and recommends a system and a connection strategy, with no material allegiance. Start the intake · How the advisory works