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Seismic Retrofitting

Standard Home Construction

The photo on the below is a diagram of how typical older, wood framed homes are constructed in our area.


On the right of the diagram, you will see a full-height concrete foundation. In these conditions the house is resting directly on top of the concrete foundation, eliminating the vulnerability of racking due to the fact that there is no existing pony walls. These homes have less weaknesses than the pony wall conditions, but are still very much capable of sliding off their foundations because they lack the proper hardware needed to resist lateral movement in the event of an earthquake.
The photo on the right is a diagram of how typical older, wood framed homes are constructed in our area.The left side of the diagram illustrates how most Seattle area homes are built, with short, wood-framed walls in the basements and/or crawlspaces. These walls are called “cripple” or “pony” walls. They span the distance between the top of the concrete foundation to the first-floor framing platform of the home, and can vary in height. This type of construction is the most susceptible to failure in an earthquake event, due the fact that the entire weight of the house sits directly on top of these short, unsecured walls that have little shear value. These unreinforced walls fail by racking, or folding over, due to excessive lateral forces during an earthquake; if these walls fail, the potential of a home falling off of its foundation is extremely high.

What is a seismic retrofit?

A seismic retrofit is the technical process of transferring the lateral forces generated from an earthquake in a building structure down to the foundation. This process is typically accomplished by modifying a buildings structural system to reduce or eliminate known seismic deficiencies.
We need to address the three main weaknesses in how a structure (home) could fail in the event of an earthquake: racking, sliding and overturning.
In order to maintain a continuous load path from the house to the foundation, anchor bolts, shear panels, shear transfer ties, and sometimes hold-downs, may be required to accomplish an effective retrofit.

How to Retrofit a Home

If you have a home that was constructed prior to 1976, in most cases, your home is resting on its concrete foundation by nothing but gravity. Prior to that date, there were no building codes that required newer homes to be attached to the foundation. Evergreen Seismic address those key major weaknesses by attaching the first-floor framing platform, down to the foundation by using the ABC’s of retrofitting; Anchor, Brace, and Connect. By completing this work, it significantly improves the chances of a total loss of your home being displaced from the foundation and most importantly, life safety. Below is a detailed depiction of the ABC’s.





In most situations, homes rest directly on a piece of lumber, called a mudsill, that is sandwiched between the concrete foundation and the first-floor platform (joists). If the mudsill is not attached to the foundation, the entire house could slide off of its foundation.This problem is addressed by adding anchor bolts through the mudsill, embedded several inches into the foundation. In addition, it is very important that each anchor bolt has a bearing plate to prevent the mudsill from splitting due to the lateral force. It is always guaranteed that homes that will need a seismic upgrade will require anchor bolts.
In situations where the home has a full-height foundation, and access is limited vertically, alternative methods will be needed, such as side anchor plates. These types of anchors require five lag screws that are installed into the sides of the existing mudsill and two anchor bolts that are bolted directly into the side of the foundation. The purpose of these anchors is to resist lateral side to side movement.
In rare situations, homes may have existing anchor bolts. These usually are not up to current building codes, due to their size and spacing, and may even be rusted through because they are not galvanized.Call us today for best seismic retrofitting services.

As previously mentioned in the first diagram above:
Most Seattle area homes have short wood-framed walls in the basements and/or crawlspaces. These walls are called “cripple” or “pony” walls. They span the distance between the top of the concrete foundation to the first-floor framing platform of the home, and can vary in height.
This type of construction is the most susceptible to failure in an earthquake event, due the fact that the entire weight of the house sits directly on top of these short, unsecured walls that have little shear value. These unreinforced walls fail by racking, or folding over, due to excessive lateral forces during an earthquake; if these walls fail, the potential of a home falling off of its foundation is extremely high.
We address this vulnerability by adding shear panels, which are attached securely with very tight nail spacing, to the cripple walls to add rigidity.Note that not shown in the diagram, in conditions where work may occur in unheated areas such as a crawlspace and some basements, round ventilation holes will be required in the shear panels. This allows air circulation throughout each stud bay to prevent future rotting. Without ventilation holes, moisture buildup can occur inside the pony walls and create rot.

The third area in which a home could fail during an earthquake is the point of contact between the first-floor platform (floor joists) and the top of the cripple wall. The only positive connection in these areas are diagonal nails, called “toe-nails), that span every few feet. As is the case when a home doesn’t have anchor bolts, this type of connection can cause a house to slide off of its foundation.
We address this vulnerability by installing shear transfer ties, or framing clips, which resists lateral forces, similar to anchor bolts. Sometimes, if there is a full-height concrete foundation, this area will be from the rim joist to the mudsill.

Additional hardware, called hold-downs, may be required in areas where overturning forces are likely. Areas where there is a limited length of wall to reinforce, or areas where there are very tall cripple walls to its length, the use of hold-downs will probably be required.
Hold-downs are a piece of hardware that is installed at the end of shear wall to resist uplift or overturning forces imposed on the wall do to “in-plane” lateral load applied at the top of the wall. They are drilled, cleaned and epoxied several inches into the concrete foundation with threaded rod, and bolted into the existing framing.

We Love Our Customers!

Matt came out to see if our house needs a retrofit and I was absolutely blown away by his honesty, knowledge and professionalism. He advised against retrofitting our house due to the newer age of the home but did provide me with a tonne of useful information that I did not come across during my research and while speaking with other retrofit companies.

Ana Lenskiy

I was extremely pleased with the seismic retrofitting job Matt and his team completed for me. The entire experience was seamless. Matt was extremely informative during the bidding process and everything was completed on time and to a high standard. The work site was cleaned everyday and work plans and schedules were clearly communicated. It's obvious that Matt and his team really care about performing quality work. To echo another review, if I could hire them for all my home renovations, I would.

Sarah Weil

They did a wonderful job on the seismic retrofitting. Our 1926 house is noticeably more stable. The workers were very pleasant to have in our home, and they cleaned up shockingly well when they were done. If we could hire them for the rest of our home improvement job we would.

Allyson Lanter

It’s a matter of time, experts say, before the Northwest shudders under another massive tectonic plate earthquake or the Puget Sound region succumbs to a big quake from one of its faults. Wood frame homes generally survive the earth shaking. But there’s a risk of them sliding off the foundation. Split-level homes also may crumble along the pony wall, sometimes called a cripple wall, that supports the upper level. Quake risks were not that well known when my home was built in Bothell in 1975. In the summer of 2022, Evergreen Seismic upgraded the house with a retrofit. This included installing anchor bolts and hold-downs into the foundation and bracing the walls in places with ¾-inch CDX plywood. Owner Matt Robinson and his crew worked in a tight crawlspace. They also removed some outside siding to brace the pony wall, upgrading the insulation before replacing the siding. Matt handled all the required engineering plans, permits and inspections. Matt showed he is skilled in retrofitting. He communicated clearly about scope of the work and scheduling. The site was cleaned after each day and neatly finished at the conclusion. The retrofit improved the safety of my home. I have documentation that I believe adds to its value. Of various people we’ve had in our home from time to time for repairs or remodeling, Matt Robinson is one of the best. I recommend Evergreen Seismic for its quality of work and service. Doug in Bothell

Doug Esser

If you need to earthquake your home for seismic activity, then you can definitely trust these guys. Matt and his team at Evergreen Seismic are very knowledgeable and do a great job.

Jeff Sherman

I loved Evergreen Seismic so much that I hardly know where to start this review. I got three bids to retrofit our 1962 home, which has a finished walkout basement and required structural engineering. All three companies were very professional and gave me comparable recommendations. Here’s why I’m so happy that I went with Matt: Quality and attention to detail: Notably, a respected competitor described Matt as “the best retrofitter I know.” During the bid process, Matt answered my extensive questions with sound, thorough information. On site, he was happy to show me the in-progress guts of the work, explaining the rationale and placement of all the hardware, additional framing, and shear panels. He also pointed out places where people sometimes cut corners and educated me on how to recognize correct, up-to-code work. Matt and Nick used high-quality materials, high-quality tools, and every element they added to our home was carefully and precisely placed. Their work passed all inspections without a hitch. Matt even paid thoughtful attention to aesthetic details, like staggering their cuts into our siding for a pleasing end result, and purchasing a color of caulk that would blend into our paint. In all matters of quality, Matt ran a tight ship. I feel safe and secure in our home, having witnessed his expertise and skill. Professionalism: Others have said it, and I’ll say it again: Matt is the consummate professional. He was easy to communicate with and responded quickly. He set clear expectations for any minor distress the siding of the house might incur during the project. He cheerfully dealt with tight spaces and a maddening tangle of defunct cables attached to the side of the house. He and Nick kept a tidy jobsite, cleaning up beautifully at the end of each day and truly leaving the interior cleaner than they found it at the end of the job. They appeared to even be packing out tiny pieces of trash like paper towels from washing their hands, rather than using the trash cans I placed out for them. Matt had to cut an old landline cable that we hadn’t planned to use, and he pointed it out right away and offered to pay to have it reconnected - a high-integrity move. Finally, he spoke very highly of his competitors without exception, which says a lot. Kindness and care: Matt is just a wonderful human to be around. He’s easygoing, straightforward, considerate, thoughtful, warm, and generous with his time. When I met Matt in the fall, I was experiencing a period of high anxiety, and I came to him with a long list of bothersome questions as I was deciding who to hire. Even though he was busy, he went far out of his way to write detailed answers, send me safety data sheets, and chat on the phone with me multiple times. Some of my questions and worries were probably ridiculous, but he treated them as if they were completely reasonable and even welcome. He never made me feel like an annoyance, and his willingness to meet me where I was at, with so much empathy and humanity, meant a lot. Oh - and he and Nick treated my five-year-old as a person worthy of as much attention and respect as an adult, which is rare! With all of that put together, we were so happy we went with Matt and honestly feel kind of bummed that we probably won’t ever get to hire him for anything else. A few final details: Matt’s bid was in the middle of the three we received, but it was within $40 of its closest neighbor, so basically identical. Contracts and payment were all quick and easy. And for anyone exercising extra caution during the pandemic, Evergreen Seismic was extremely covid-conscious. The team was fully-vaccinated and wore high-quality masks for the entire duration of the job. I don’t even know what their faces look like. Even though they were working outdoors in the fresh air with no one else around, they always had a mask around their neck to be pulled up within a moment’s notice when I popped over to greet them. A+!

Jen Sharber Matsuda

Evergreen Seismic recently completed an earthquake retrofit on our home. We chose the company in part because of great online reviews and we were not disappointed. Matt clearly explained the entire process and patiently responded to all of our questions. The work went smoothly and efficiently, was completed ahead of schedule, and the daily cleanup was amazing. Most importantly (for us anyway), the person who sold us on the job (Matt) was also part of the working crew. I wholeheartedly recommend Evergreen Seismic for earthquake retrofitting. From start to finish, this was by far the smoothest construction job we have experienced during the twenty years that we have lived in our home.

Ruth Anderson

We used Evergreen Seismic to do an earthquake retrofit on our 1979 build home in Kent, WA based upon great customer reviews. We were not disappointed! Matt and his crew were very professional and showed up as promised. We were promptly informed when on one occasion they were a bit late due to traffic congestion. The work was performed to our satisfaction. The daily cleanup was impeccable. Matt was able to answer all questions that the inspector asked to his satisfaction. The Company actually went over and above what the structural analysis indicated was needed (additional bracing was installed). The majority of the retrofit was done on the exterior of the house in pouring rain! However, to our amazement, this did not in any way slow down the crew! A truly professional Company. We can recommend Evergreen Seismic without any hesitation.

Subir Lahiri

Exceptional service from Evergreen Seismic. I met Matt at an info session on seismic retrofitting hosted by the city of Seattle. It took me a year or so to reach out to him. I was impressed form the start. Matt was more than willing to coach me on doing the project myself, if I wanted to take it on. But in given the complexity of our project, I preferred to hire Matt and his crew. They did a great job, and even did some prep that I was supposed to do but couldn't because of a recent back injury. Very straightforward, informative, and considerate service. I'd hire Matt again without hesitation.

Jeff Maggioli

Matt did the seismic retrofit of our single-family residence back in January when we were finishing our basement. I cannot speak highly enough of him and Evergreen Seismic. Matt has undoubtedly been one of the best contractors we've worked with. He's an excellent communicator and really goes above and beyond on all fronts. He does what he says he's going to do, when he says he's going to do it, and finishes when he says he's going to finish, all at an extremely competitive price. He's knowledgeable of seismic retrofitting and has a very streamlined process nailed down. If you are thinking of doing a seismic retrofit, Evergreen Seismic is DEFINITELY the way to go!

Austin L
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