fbpx

Does my Portland Home need a Seismic Retrofit?

You’ve probably heard that the Portland metro area is at high risk for earthquakes. But did you know that in spite of this, not every home in Portland is built to withstand a major seismic event? If you’re concerned that your home may be at risk during an earthquake, don’t panic. A seismic retrofit can modify your home to be safer and more structurally secure the next time an earthquake hits Portland.

As a remodeling firm that specializes in customized home renovations, our team at Lamont Bros. has worked on hundreds of homes across the Portland area. We’ve found that in many cases, a home remodel presents a good opportunity to also perform a seismic retrofit. The challenge for most homeowners is knowing whether or not their home needs it.

In this article, we’ll help you explore the fundamentals of seismic retrofit renovations to decide if your Portland home needs one. Once you’ve finished reading, you will be able to more accurately assess the seismic needs of your home. Specifically, we’ll discuss:

What is a seismic retrofit and why might you need one?

The Portland metro area sits within the Cascadia Subduction Zone, an area of relatively high seismic activity. This is due to the subduction of the Juan de Fuca plate under the North American plate. This 600-mile-long tectonic fault runs along the coast of Washington, Oregon, and Northern California.

Earthquake Risk Map of the United States. Note that the West Coast is at high risk for seismic activity.

On average, the Cascadia Subduction Zone experiences a major earthquake every 230 years. However, the last time the area experienced a seismic event was a 9.0 magnitude earthquake in the year 1700, over 300 years ago. As a result, geological experts estimate that we are overdue for another major earthquake, and the next one could happen very soon. Currently, there is an estimated 37% chance of a 7.1 magnitude earthquake or greater in the next 50 years.

A seismic retrofit is a renovation project that reinforces the structure of a building to better withstand a seismic event.  Due to the high earthquake risk in the region, many Portland homeowners are choosing to perform seismic retrofits on their homes. Here are a few reasons why you might want to consider doing the same.

A seismic retrofit protects you and your home

75% of earthquake-related deaths are caused by building collapse. Because Portland is in a high-risk earthquake zone, a seismic retrofit is a wise decision for any home that does not meet modern structural safety requirements.

In Oregon, seismic requirements were not implemented into the state building code until 1993, meaning that homes built before then are at higher risk of damage in an earthquake.  By reinforcing the home’s structure to meet the current building code, a seismic retrofit can greatly reduce the risk of structural damage or collapse. It can also save you between $10,000 and $200,000 worth of repairs down the road.

This means that if the big one strikes within your lifetime, you can have confidence that your home will protect you and your family.

A seismic retrofit can improve your insurance coverage

Due to the earthquake risk of the Portland area, many homeowners feel more at peace having insurance in case their home sustains damage. Unfortunately, most homeowners’ insurance policies do not cover seismic events.

If you want to make sure your home is covered against earthquake damage, you’ll likely need to purchase a separate policy. The catch is that these policies require the home meets certain structural requirements. Proof of a seismic retrofit is usually the only means of securing earthquake coverage for homes built pre-1993.

It’s also worth noting that most earthquake policies offer a percentage deductible rather than a fixed amount. This means that the higher the repair cost, the more your deductible will be. Since a seismic retrofit reduces the expected cost of repairs, it can help you avoid a higher deductible.

A seismic retrofit increases the value of your home

By performing a seismic retrofit, you decrease the risk associated with owning the home. The home now poses less financial risk of ownership because an earthquake cannot incur as much damage and, by extension, repair costs. As a result, the value of the home increases.

In fact, a 2020 study conducted at the University of Colorado concluded that a seismic retrofit increases the resale value of a home by approximately 10%. Most seismic retrofits cost between $5,000 and $15,000, and very few cost more than $30,000. With home values in Portland averaging $525,000, a seismic retrofit could add $52,500 to the average home.

What are my options for a Seismic Retrofit?

When performing a seismic retrofit on a home, there are two ways to approach the project. Depending on the design of your home and the methods used to build it in the first place, one approach may work better than the other.

The most common concern in a seismic retrofit is addressing the structural integrity of cripple walls. A cripple wall is a framed wall that raises the vertical level of the home between the floor joists and the foundation. During an earthquake, these cripple walls may collapse.

A home with cripple wall construction. Note the framed walls between the foundation and the bottom of the floor joists above.

Prescriptive Seismic Retrofit

A prescriptive seismic retrofit involves following a set of pre-determined guidelines for strengthening a building’s structural elements to better withstand seismic activity. The goal of the prescriptive approach is to address the most common seismic structural concerns in a straightforward, formulaic method. It’s often looked at as a “one size fits most” approach to performing seismic retrofits.

The prescriptive approach is only effective when used on homes that were built using the standard practices of their day. Single-family suburban homes from the mid-1900s are excellent candidates for prescriptive seismic retrofits.

Under the prescriptive method, a seismic retrofit may involve the following upgrades:

  • Anchoring the mudsill (lowest structural sill) to the foundation
  • Installing horizontal blocking between studs
  • Adding sheathing over the studs to increase lateral rigidity
  • Attaching 90-degree angle brackets from the rim joist to the cripple wall
  • Fitting post cap brackets to the interior support posts

Custom Engineered Seismic Retrofit

In some cases, a prescriptive retrofit will not provide the amount of reinforcement required to make a home safer from earthquake damage. In these cases, the home requires a custom-engineered seismic retrofit.

Unlike prescriptive seismic retrofits, custom-engineered seismic retrofits are developed on a case-by-case basis. They involve a range of retrofit measures specifically tailored to address the unique needs of the home.

Custom-engineered seismic retrofits may involve common procedures such as adding or reinforcing the foundation, installing bracing or shear walls, and upgrading roof or floor structures. However, they may also involve more unique solutions, such as installing steel moment frames, pouring new foundation footings, strapping hazardous chimney structures, or other measures identified through the detailed engineering analysis and design process.

How to tell if your Portland home needs a seismic retrofit

The best way to tell if your home needs a seismic retrofit is to have it professionally inspected. However, there are a few key indicators that you can examine yourself to begin to understand whether a retrofit is right for you.

Your home was built before 1993

Although Oregon introduced its first building codes in 1974, the regulations pertaining to seismic protection were not introduced until 1993. As a result, Portland homes built prior to 1993 are considered at higher risk for earthquake damage and would likely benefit from a seismic retrofit.

The home’s foundation has cripple walls

Cripple walls are a major hazard when it comes to seismic building safety. Modern homes are typically much safer because the floor system sits directly on top of the foundation. However, with cripple walls, the floor system is elevated several feet above the foundation. Without the proper bracing, those cripple walls can collapse in an earthquake and bring the entire house crashing down.

There is a soft story living space in the home

A soft story is a living space that sits above an open area below, such as a garage or large living room. Because the lower story does not have any internal support posts, it relies only on the walls to hold up the structure. While these walls are built to withstand earthquake forces in modern homes, that’s not always the case in old homes. As a result, older homes with soft stories may require retrofitting.

The home is on a sloped lot

Homes built on a hillside usually have uneven foundation walls — the uphill walls tend to rise higher than the downhill ones. Because of this, the home may experience more lateral forces to one side, causing more damage to the structure during an earthquake.

You plan to remodel your basement

A seismic retrofit can be invasive. It requires a lot of alterations to the foundation structure, and accessing the necessary structural members requires a lot of demolition. So, if you’re planning to remodel your basement, it often makes sense to tack a seismic retrofit onto the project. That way, you don’t have to come back later and tear up your brand-new basement to make your home safer.

Want more information on basement remodeling?

Now that you know more about seismic retrofit projects, do you think your Portland home might need one? If so, start thinking about what other changes you might want to make to your foundation or basement. Check out some of Lamont Bros. basement remodel projects to see what other Portland homeowners are doing to bring new life to their homes.

Want to talk with a professional designer about a seismic retrofit on your Portland home? If so, click the button below to schedule a free design consultation with a member of our team. We’ll help you navigate the challenges of remodeling your home so you can be confident in the decisions you make.