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.

Full Height Foundation
Pony Wall Conditions

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.

Anchor
Brace
Connect
Overturning

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.

Our Customers Love Us!

      
   Evergreen Seismic, LLC
   72 Google reviews 
  Write a review 
  
 
 
   
 
 
       Posted on Google  
   
   B Snead 
 
 
 
 Trustindex verifies that the original source of the review is Google. I came to know that my house was vulnerable to seismic events so I did some research on how to lessen the risk.  The things it seemed I needed were things I didn't want to do myself so I looked around for a vendor and came upon Evergreen Seismic.  Matt came out and looked at my house and recommended mediation that was almost exactly what my research had indicated and explained the technology in terms of my particular situation, which was appreciated.  He even explained other steps he didn't think were needed, which he probably could have talked me into.  I appreciated his honesty and knowledge.  We scheduled the work and he did exactly what he said he'd do.  I would recommend Matt and his company to anyone.
  
 
      Posted on Google  
   
   Warner Asch 
 
 
 
 Trustindex verifies that the original source of the review is Google. We had a fantastic experience with Evergreen Seismic. From the initial estimate through the completed retrofit, everyone we worked with was professional, responsive, and easy to communicate with. Matt was especially great to work with—he took the time to answer our questions, explained the process clearly, and made us feel confident every step of the way. We never felt pressured and always felt like we were in good hands. The crew was punctual, respectful of our home, and completed the work efficiently while keeping the area clean and organized. We also chose to have an automatic seismic gas shutoff valve installed, and they made sure we understood how it worked before they finished. Our home was built in 1959, so it gives us real peace of mind knowing it has now been properly seismically retrofitted. The quality of the work and customer service exceeded our expectations. Thank you, Matt, and the entire Evergreen Seismic team! We highly recommend Evergreen Seismic to anyone looking for a knowledgeable, trustworthy, and professional company.
  
 
      Posted on Google  
   
   Blaine Robbins 
 
 
 
 Trustindex verifies that the original source of the review is Google. Matt did a seismic retrofit for us recently. He was communicative and responsive throughout the entire process and did fantastic work, often going above and beyond what was necessary. I would highly recommend for anyone thinking about doing a retrofit.
  
 
      Posted on Google  
   
   Jonathan Glick 
 
 
 
 Trustindex verifies that the original source of the review is Google. I'm very happy with the seismic retrofit work Evergreen Seismic did at our home. They were clear about the scope of work and reasonably priced compared to other providers. Matt and Phil were a pleasure to work, worked around our schedule, and got the job done quickly. They work with a well-known engineering company so I'm confident the work meets a high standard.
  
 
      Posted on Google  
   
   Alex 
 
 
 
 Trustindex verifies that the original source of the review is Google. Matt & Phil did an absolute fantastic job seismically retrofitting our home. There were several stages in the process where the team went well above and beyond what was required. Generally it is hard to find Contractors you can trust and Evergreen Seismic is absolutely among the few that you could trust to do a great job!
  
 
      Posted on Google  
   
   Brian Moynihan 
 
 
 
 Trustindex verifies that the original source of the review is Google. Matt and Phil went above and beyond on the seismic retrofit of our 1919 home.  They repaired some rot that was discovered during the process, and still got the project done within the estimated number of days.  They also replaced some questionable posts and strengthened a compromised beam - things that other contractors did not include in their bid.  Very reasonably priced.
  
 
      Posted on Google  
   
   Beck Royer 
 
 
 
 Trustindex verifies that the original source of the review is Google. Excellent professional and a knowledgeable company!  Matt was prompt, and helped us with an insurance renewal and on site visit!!  Great all round and honest Beck
  
 
      Posted on Google  
   
   Cameron Skaggs 
 
 
 
 Trustindex verifies that the original source of the review is Google. Matt and his team were very professional. He helped explain the process and was very transparent with everything. They worked quickly too. I'd recommend them unhesitatingly to anyone looking to retrofit their house for earthquakes
  
 
      Posted on Google  
   
   Jaymes Dee 
 
 
 
 Trustindex verifies that the original source of the review is Google. Matt and his team were beyond helpful during our journey to seismic retrofit our 1953 home. At first I was certain I would be doing the retrofits and Matt was gracious enough to come and venture through my crawlspace with me and give me pointers. When life and all of it's entanglements got in the way, Matt and his team were able to knock out the work expeditiously for a very reasonable price. My family and I feel safer because of the work they did. 10/10 recommend.
  
 
      Posted on Google  
   
   Erik Peterson 
 
 
 
 Trustindex verifies that the original source of the review is Google. I can't say enough great things about Evergreen Seismic. If I could, I would give them 6/5 stars! Matt was such a pleasure to work with. He was so knowledgeable, patient, responsive, generous with his time, and such a resource. He explained complicated topics into basics I could understand, and also adjusted his approach based on some constraints we had. If you are looking to do any kind of seismic retrofit for your home, you should reach out to Matt and his team at Evergreen Seismic. Just...wow. So refreshing to work with some true professionals.

Seismic Retrofitting

Standard Home Construction

What is a seismic retrofit?

How to Retrofit a Home

Our Customers Love Us!

Let’s make your home safer

Get a professional evaluation