Does Your House Need Seismic Retrofitting? We Can Help.

Family-Owned Business

We’re a family-owned business whose mission is to create a more seismically prepared Portland. In designing and implementing a retrofit plan tailored specifically to your home, we hope to shorten the recovery time for Portland after the next Cascadia subduction earthquake. Our work strengthens homes to a degree at which homeowners can shelter in place after a moderate-to-high seismic event.

Is Your Home Safe?

Houses built prior to 1974 were not required to be anchored during construction. In the decade following the 1974 code revisions, houses were being built by contractors with little to no knowledge of how to properly anchor a house, leaving homes built during this code cycle still vulnerable to seismic activity. Click here to see an example of how a modern home is at risk for damage in an earthquake.

In the market for a new house?

NW Seismic offers a free pre-purchase inspection, especially important with houses built prior to 1930. In our experience, house inspectors are in no way qualified to evaluate foundations, so we suggest having us look at the house before you pay for an inspection.

NW SEISMIC SERVICES

Seismic Retrofits

Seismic retrofitting is a process of transferring lateral loads generated in an earthquake from the house to the foundation.

To keep a house from falling off its foundation in an earthquake, seismic retrofitting strengthens three different areas of the house. These areas are all located in the basement and/or crawl space. If any one of these three areas are not adequately retrofitted, the house will be susceptible to major damage in an earthquake.

Foundations

Does your home have a brick, block or crumbling foundation? Here at NW Seismic we have many solutions to your problem.

Some houses have brick, unreinforced concrete block or terra cotta block foundations. Most have a poured-concrete foundation. Pre-1940 foundations were mixed with sand scooped and unwashed from the river, creating a crumbly foundation. If any of these issues apply to your home, we can help. 

Gas Valves

Historically, post-earthquake fires have been responsible for a lot more home damage than from the earthquake itself.

An automatic gas shutoff valve shuts off your gas at the meter during an earthquake. Installed on the meter, it shuts off the dangerous gas before it enters your house. The meter is designed to know the difference between passing trucks and buses, or being bumped, and an actual earthquake.

Egress Windows

Are you thinking of converting your basement into a cozy living space? You'll most likely need an egress window.

Most jurisdictions require an egress window be installed in a basement if you are planning on having one or more sleeping rooms. We’ll excavate outside, cut the concrete, install the window, and pour a concrete window well. This process takes less than a week from start to finish.

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HOMES WE RETROFITTED IN 2020
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PRE-1974 HOMES NON-RETROFITTED
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EST. DAMAGE TO PORTLAND HOMES

SOME FAQs

How long does a retrofit take?

Ultimately it depends on a number of variables including size and construction of the house, the number of workers on site, and job-specific obstacles. Often it takes 1 day for an unfinished basement or crawl space, 2-3 days for houses with cripple walls, and about 1 week for finished basements. Sometimes we need to reverse-engineer houses that were designed to maximize views and were built prior to a building code revision in 1994 to determine the designed load values and then re-engineer the structural design to get closer to meeting the current code requirements, and these can be somewhat drawn out projects.

I read that the anchors need to be 4′ apart. Is that what you do?

No, we use an engineered equation to determine the lateral loads for your particular house and the amount of hardware, or resistance, will be equal on all 4 wall lines. If your house is square, the spacing will be equal on each wall. If it’s rectangular, the hardware will be closer together on the short walls and further apart on the long walls. 4’ spacing refers to something called “prescriptive path,” the origins of which can be traced to a committee set up by the Association of Bay Area Governments after the Loma Prieta earthquake (it included engineers, contractors and, not surprisingly, hardware manufacturers, and it went on for 5 years), and is really just “rule of thumb.” It works occasionally on square houses with wood siding and cedar or comp roofing, no additions, few sill plate splices and no more than two floors above the basement or crawl space level.

Do you retrofit from inside or outside?

Either. Surprisingly, the cost tends to be fairly equal, whether we do it from the inside or outside, due to the increased load rating, or strength, of exterior hardware, and exposure to the elements, even when we need to demo and repair the interior finishes. The latter requires hardware that’s either hot-dip galvanized or stainless steel. The flat hardware we use on the exterior, the Simpson FRFP, has a 20% higher load rating than that of the interior hardware, Simpson URFP. As a result, we need to use more of the interior hardware to achieve the same result.

What is the code for a seismic retrofit in Oregon?

There is none. Portland has a “seismic retrofit program,” as do other jurisdictions on the West Coast, including Seattle (Project Impact), the Association of Bay Area Governments (Plan Set A), and Los Angeles (Earthquake Brace and Bolt) which relies on “prescriptive path,” or rule-of-thumb (also known as Retrofitting for Dummies). There is no math involved in the retrofit design, and it fails to take into account the shape of the foundation (see the question: “I read that anchors need to be 4’ apart. Is that what you do?”), among other glaring omissions.

Any Questions?