How long does a seismic retrofit take?

A standard bolt-and-brace retrofit on a typical house often takes a few days. Engineered retrofits and foundation repairs take longer, plus time for permits and inspections.

Does a retrofit fix foundation cracks?

No. A retrofit strengthens the connection between the house and its foundation. Cracked or crumbling foundations need separate repair, ideally before or together with the retrofit.

How much does it cost to bolt a house to its foundation?

FEMA reports about $4,000 to $25,000 for homes in Portland’s demonstration project. Prescriptive bolt-and-brace retrofits in California are commonly about $3,000 to $7,000 for qualifying houses.

How do I know if my house is bolted?

Look in the crawl space along the sill plate, the wood resting on the foundation. Anchor bolts with nuts and washers, or metal plates, should appear at regular intervals. If you see none, your house is likely unbolted.

What is a cripple wall?

A short wood wall between the foundation and the first floor, enclosing a crawl space. Unbraced cripple walls can collapse sideways in an earthquake.

Do I need a permit for a seismic retrofit?

Many cities, including Portland, require a permit and inspection. Ask your contractor or building department.

Seismic Retrofits: Bolting a House to Its Foundation

Why older houses slide off their foundations

Many houses built before modern seismic codes simply sit on their foundations. The wood sill plate rests on the concrete or masonry with few or no anchor bolts. In some houses, short wood walls called cripple walls stand between the foundation and the first floor, enclosing a crawl space, and those walls have little bracing. In strong shaking, an unbolted house can slide off its foundation, and unbraced cripple walls can fold over, dropping the house by a few feet. The damage is often severe and expensive even when the rest of the house holds together.

A seismic retrofit addresses exactly those two weak points: it bolts the sill plate to the foundation and braces cripple walls with structural panels so they cannot collapse sideways.

Which homes are candidates?

Wood-frame houses built before local codes required anchor bolts and cripple wall bracing, often before about 1980 depending on the area
Houses on a raised foundation with a crawl space, especially with cripple walls
Houses where you can see no anchor bolts (or only a few) along the sill plate in the crawl space
Houses in regions with significant earthquake risk, such as the Pacific Northwest and California

Houses on slabs, very old houses on unreinforced brick or stone foundations, and houses on steep slopes can need engineered solutions beyond a standard retrofit.

What Portland learned

With the Cascadia Subduction Zone offshore, Portland has paid close attention to residential retrofits. FEMA and the Portland Bureau of Emergency Management ran a seismic demonstration project that retrofitted more than 100 homes, focusing on single-family wood-frame houses with unbraced cripple walls or sill plates that were not bolted to the foundation. FEMA reports that bolting houses to their foundations in that project could cost anywhere from about $4,000 to $25,000, depending on the house. The Oregon Construction Contractors Board publishes a consumer guide to earthquake retrofitting for homeowners considering the work. See foundation repair in Portland.

What the work involves

Assessment. A contractor or engineer looks at the crawl space, foundation condition, sill plate, existing bolts and cripple walls.
Foundation check. Bolts only help if the foundation can hold them. Crumbling concrete or brick may need repair first.
Anchor bolts or plates. New anchors are installed through the sill plate into the foundation at set spacing.
Cripple wall bracing. Structural plywood or similar panels are nailed to cripple walls with a specified nailing pattern, with vent holes as needed.
Connections. Framing connectors may be added between the sill, cripple wall and floor framing.
Inspection. Where a permit is required, the city inspects before the crawl space is closed up.

Standard plans vs. engineered retrofits

Some areas offer prescriptive retrofit plans for typical houses: if your house meets the criteria, the contractor follows a standard set of details. California’s Earthquake Brace + Bolt program, for example, describes a retrofit that bolts the house to the foundation and braces cripple walls with plywood, and lists typical contractor costs of about $3,000 to $7,000 for qualifying California houses. Houses outside those criteria, such as tall cripple walls, hillside homes or unusual foundations, need an engineer’s design and usually cost more.

Published costs

Item	Published range	Source
Bolting a house to its foundation, Portland demonstration project	about $4,000 – $25,000	FEMA
Typical prescriptive bolt-and-brace retrofit by a contractor (California program)	about $3,000 – $7,000	California Residential Mitigation Program

Published figures for orientation only, not quotes. The contractor you are connected with sets the price after an inspection.

Questions to ask a retrofit contractor

Does my house fit a standard retrofit plan, or does it need an engineer?
What condition is my foundation in, and will it hold new anchors?
How many anchors, what type, and at what spacing?
Will you brace cripple walls, and how will you handle ventilation?
Is a permit required, and will you schedule inspections?
Are you licensed? In Oregon, check the Construction Contractors Board; in Washington, Labor and Industries registration.

Retrofits and other foundation problems

A retrofit strengthens the connection between house and foundation; it does not fix a foundation that is cracked, settling or crumbling. In older homes, it often makes sense to combine a retrofit with repairs to the foundation itself, for example replacing crumbling sections, adding footings or fixing drainage. Doing both at once avoids opening the crawl space twice. See stone and brick foundation repair for older masonry foundations and foundation drainage for water problems.

Grants and insurance

Some states and cities have offered grants or incentives for residential retrofits at different times, and some earthquake insurance programs offer premium discounts for retrofitted homes. Programs change, so check with your city’s emergency management office or your insurer for what is available now. Keep the permit, photos and invoices; they document the work for insurance and resale.

Can you do it yourself?

Some prescriptive retrofit programs allow homeowners to do the work themselves under a permit, and the California program notes that do-it-yourself retrofits can cost less than contractor work. It is physical work in a tight crawl space, with drilling into concrete, precise nailing patterns and inspections. Mistakes such as the wrong anchor, missed nails or blocked ventilation reduce the benefit. Most homeowners hire a contractor, at least for the assessment, and have the finished work inspected so the permit and photos document what was done.

What a retrofit does not do

A retrofit reduces the chance that your house slides off its foundation or drops when cripple walls collapse. It does not make a house earthquake-proof, and it does not protect chimneys, contents or utilities. Securing water heaters, anchoring tall furniture and knowing how to shut off gas are separate, inexpensive steps worth taking at the same time.

Seismic Retrofits: Bolting Your House to Its Foundation and Bracing Cripple Walls