How much does it cost to retrofit a home for earthquake protection?

If your home is located in an area known to be hit by earthquakes, you may want to consider having it seismically retrofitted to help protect it from serious damage in the event of an earthquake. Homes that were built prior to the 1970s were not constructed with the right type of technology or techniques to help protect them from earthquakes, and even some newer homes may have been built without the latest in protection techniques. This means that older homes should undergo retrofitting to brace and strengthen them to withstand an earthquake.

Earthquake retrofitting a house costs, on average, $3,000 to $7,000 with the average homeowner spending around $5,000 on retrofitting a standard 1,500 sq.ft. two-story home with cripple walls ¹.

Earthquake retrofitting

Why is earthquake retrofitting so important?

Even if your home has gone through an earthquake in the past with minimal damage, there is no way to predict exactly when and where the next earthquake will strike, or how much damage it could do. Older homes that have not been adequately bolted to their foundations could sustain hundreds of thousands of dollars worth of damage in the event of a major earthquake. This is because the home may actually separate from its foundation during seismic activity.

Most home interiors and upper portions actually come through earthquakes alright, with only superficial damage that can be easily repaired. But homes that are not secured to their foundations can have major structural issues following an earthquake, making them unsafe to enter or continue living in until they have been repaired.

By retrofitting your home, you are minimizing the damage that could occur with the next earthquake, ensuring that your home and family stay better protected, and minimizing recovery costs.

Cost factors of earthquake retrofitting

There are a lot of factors that go into determining the cost of your retrofit. The age of your home is the first–the older the home, the more work that will need to be done to strengthen it. Your location will also play a role–homes located in areas on or near cliffs or water may require additional support. If your home has been hit in the past or if the area in question has been impacted by heavy earthquakes before, this can also play a role in determining your cost, as your home may need more work. Larger homes will also typically cost more to retrofit than smaller homes, as there is simply more work to be done.

Finally, the type of construction your home has may play a role. Homes with a cripple wall ¹ will cost more to retrofit than homes without one.

Engineer consultation

To determine the exact extent of the work that needs to be done, most companies will start the process with an engineer consultation. They’ll take a look at your home, where it’s located, what type of foundation and structure it has, and make a determination for the best way to proceed. Foundation bolting ² is common, but it’s only one step for many homes, and an engineer can help determine what the best path will be.

Many companies will provide this service for a fee that will be recouped if you proceed with the work. For example, you may pay $500 for this initial service, but the final cost of the project will be $500 less, absorbing the fee.

Retrofit strategies

Most retrofitting strategies are applied on a case-by-case basis, taking into consideration the type of structure and its current condition. Generally, there are several techniques that are done to retrofit a structure, but an apartment building will be tackled differently than a single-story home, while two-story structures may require a different strategy, depending on how they were each constructed.

For this reason, you may find that when you call about foundation bolting ², you may be offered a different strategy. A few examples of this may include adding hold downs to shear walls to resist overturning if the home is top-heavy, and reinforcing a foundation with additional concrete prior to bolting.

Each home will have its own strategy mapped out, which is why it’s important to have an engineer work with the contractor at the start of the project.

Retrofitting techniques and main steps

Keeping in mind that each structure is different, most homes will have a few different techniques done to help secure the home to the foundation.

There are some basic steps that most homes will need to have done. Keep in mind that some structures may benefit from more or fewer steps than this.

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Foundation bolting

This is the bare minimum piece of earthquake retrofitting: anchoring your home directly onto the foundation. This is what helps keep your home from sliding off the foundation and being damaged during an earthquake. This is sometimes known as anchor bolting and literally means that large bolts are sunk through the base of your home and into the foundation.

Anchoring to mudsill

The cripple wall ¹ of your home’s crawl space is anchored onto the mudsill ³ of your foundation. This is part of the foundation bolting ² process, as the cripple wall ¹ and mudsill ³ can both slide right off the foundation, so the mudsill ³, cripple wall ¹, and the foundation all need to be bolted together for the best stability.

Cripple wall bracing

The cripple wall ¹ itself needs to be reinforced and braced, usually with plywood ⁴. On its own, most older cripple walls ¹ can not handle the movement that occurs during an earthquake, and that may lead ⁵ to collapse or to the home falling from the foundation. By bracing the cripple walls ¹, it minimizes movement and ensures that the home is more secure.

Cripple wall anchoring to the floor

It isn’t enough to bolt the cripple wall ¹ to the foundation; it also needs to be bolted to the floor above. This is done through shear bolting, but may also involve creating a frame on the interior of the cripple wall ¹, and bolting this to both the wall and to the floor above.

Shear wall reinforcing

Sometimes in top-heavy structures, such as an apartment above a garage, the shear walls themselves need extra reinforcement. This can be done on both the vertical and horizontal surfaces of the upper story, usually using steel grates, but can sometimes be done with additional stud reinforcement on the interior of the walls.

Cost

Keep in mind that there can be a range of costs for each of these steps, that not every step is always required, and that your project may have higher or lower costs for each one depending on multiple factors.

In the following table, you will find the average cost for each technique used on a 1,500 sq.ft. two-story home:

Homes without cripple walls

Some homes do not have cripple walls ¹, which can mean a lower cost for the overall project, as bracing and bolting of this section are not needed. However, the joists of the home will still need to be bolted to the mudsill ³ and to the foundation to help prevent the home from sliding off. This includes the floor joists, rim joists, and end joists. All of them need to be bolted to the mudsill ³ and foundation in order to secure the home. This is because homes without a cripple wall ¹ are at more risk for damage than those that have them.

Soft story situations

Apartment buildings and multi-family homes have additional considerations in earthquake retrofitting. In this case, a “soft-story building” is considered any building tall enough that it would sway during an earthquake, causing cracks and weakening the walls and foundation.

In this situation, steel beams are usually used to reinforce the structure and prevent any swaying from occurring. The same foundation bolting ² should occur, but inner reinforcement of the walls is also necessary to prevent structural damage.

Retrofitting based on the foundation

The foundation that your home is built on will play a role in retrofitting as well. Brick foundations cannot be reinforced and bolted the same way that a concrete foundation can. Complicating matters, some concrete foundations, too, are too old or too thin to bolt in their current condition. In this case, a hole is generally dug and additional concrete added to help strengthen the foundation before the bolting can occur.

Labor costs of earthquake retrofitting

In most cases, professionals charge by the service being performed, rather than by the hour. This is because there can be a wide range of time required for a retrofit, depending on what’s found when the walls are opened. It’s not uncommon for a retrofit to take between a few days and a few weeks for the average home. From this end, it is not uncommon for the labor to cost up to 70% of the total for the project for major retrofits, especially those on a hillside, which can cost up to $10,000. For most homeowners, you can expect that out of the $5,000 total, you are paying at least $3,000 in labor, if not more.

Earthquake retrofitting materials

The materials used on each job may vary, but generally, you can expect to see the following:

Enhancement and improvement costs

Seismic review

If you are unsure of the risk to your property, you can opt to have a seismic review done of your area, which can tell you how you may be impacted. Keep in mind that it can be impossible to predict damage. A review can cost between $100 and $500, depending on the level ⁶ of detail.

Additional considerations and costs

• In most cases, earthquake retrofitting is not covered by insurance, but you may qualify for a lower insurance rate once it’s done.
• All professionals who work on earthquake retrofitting your home should be licensed and have a permit for the job. Make sure you follow up to confirm both.
• PACE financing may be available to you to help meet the costs of the retrofit. This is an affordable financing option that is available for upgrades that include energy efficiency and storm protection. This is not a loan, but a property assessment, that allows you to borrow the money based on the property you are updating at a low-interest rate. Speak to your contractor for more information.
• There are some DIY options available for retrofitting, including bracing your cripple walls ¹ with plywood ⁴ and bolting your foundation. Keep in mind, however, that these retrofits may not be enough without an engineer to look over the project first.
• To prepare for an earthquake, make sure you secure heavy objects and appliances with brackets ¹¹ or straps, prepare a survival kit with food and medical supplies, and keep it in a safe location in your home where you can take shelter during an earthquake. This may be in a doorway or a reinforced area of the home.

Remodeling Terms Cheat Sheet

⁴ Plywood: An engineered construction material manufactured from thin slices of wood glued together in alternating grain patterns for strength

⁵ Lead: A naturally occurring heavy metal that is highly toxic to humans, and has been used in paint, gasoline, piping, and other applications

⁷ Mortar: A mixture of Portland cement or lime or a combination of both, sand, and water used to bind bricks, stones, and concrete masonry units together

⁸ Footing: A support for the foundation of a house that also helps prevent settling. It is typically made of concrete reinforced with rebar, but can also be made of masonry or brick. It is usually built under a heavier part of the house like a wall or column, to distribute the weight of the house over a larger area.

⁹ Concrete slab: A flat area of concrete that can be used for a variety of purposes, such as a patio or a driveway

¹¹ Brackets: A support that projects outward from one surface to hold another surface to it, such as attaching a shelf to a wall or piece of furniture. Brackets can also be used to strengthen joins between two materials