Is Your Home Prepared for an Earthquake?
In the San Francisco Bay Area it’s only a matter of time for an earthquake to hit. You don’t know when. With all the earthquake fault lines the potential for a serious earthquake is always there. That’s why it’s important to make sure your home is prepared to survive.
When the ground shifts, your home may not jump off the foundation, but it can slide with the movement of the quake. And, disaster! Your home is off the foundation, supported by nothing.
Many new homes are fitted or properly anchored to deter earthquake destruction. But, if you have an older home, you owe it to yourself to get earthquake retrofitting.
Earthquake Brace & Bolt Can Save Your Home
You can take steps now to secure your home. Prepare with relatively inexpensive earthquake seismic safety retrofit improvements. They are critically important in the event of an earthquake.
There are two critical components to the retrofit process to protect your home. Depending on how your home sits on the foundation you may need one or both to secure your home.
Anchor Bolts
Most earthquake damage actually occurs when unsecured buildings slide off of their foundation. Bolting your home down helps prevent sliding.
If the wood frame of the house sits directly on the foundation (known as a “stem wall”) in the crawl space under the house, this house would need a “bolt-only” retrofit, where the foundation is bolted to the wood frame of the house.
Bolting is when large anchor bolts or foundation plates are used to bolt the wooden frame of the house to the concrete foundation, to strengthen the connection between the two.
Anchor bolts are installed through the mudsill (bottom piece of wall framing) securing the wood structure to the foundation, and the anchor bolts are installed into holes that penetrate vertically into the concrete foundation stem wall (called wedge anchors, a common trade name for these retrofit anchors is “red head”). A washer is placed below the bolt head to keep the nut from stripping off the bolt during a seismic event.
Cripple Wall Shearing
If there are short (4 feet or less) walls between the wooden frame of the house and the foundation (known as “cripple walls”) in the crawl space under the house, the house needs a “brace and bolt” retrofit. A brace and bolt retrofit iinvolves bracing the cripple walls with sheets of plywood or OSB (oriented strand board) sheathing, then bolting the foundation to the wood frame of the house.
Oriented strand board (OSB) is a type of engineered wood similar to particle board, formed by adding adhesives and then compressing layers of wood strands in specific orientations.
- Bracing: plywood or OSB sheathing is attached along the cripple walls to strengthen the structure between the house and the crawl space.
- Bolting: large “anchor bolts” or foundation plates are used to bolt the wooden frame of the house to the concrete foundation, to strengthen the connection between the two.
If your house is set on the foundation like this, you need the braces and bolts. Otherwise, just like dominoes standing up in a row, when one falls and hits the other, they ALL fall. A similar thing happens to houses during earthquakes, the wall start shaking back and forth, and side to side. Sometimes they are displaced far enough that instead of coming back to center, they just keep going and the whole wall laterally falls to the ground.
The Time is Now! Prevent, Preserve, and Protect Your Home
Catastrophic repairs are WAY more expensive and severe than preventative repairs, so just do it now!
You need to do it now. Tomorrow may be too late, if you’re saying, I’m going to do it tomorrow.
If you are a homeowner who is an experienced “do-it-yourselfer,” you can do the retrofit as an owner-builder. You will be the general contractor for your project and assume responsibility for the overall job. However, as an owner-builder, the value of your labor is not a recoverable cost and tools should be rented not purchased.
It’s a dirty job and you’ll need some special tools like like a right angle impact drill that drills and jackhammers at 90 degrees to create the holes in your foundation stem wall.
Most homeowners decide to hire a contractor to do the retrofit work instead of doing it themselves. If you hire a contractor to do the retrofit work, use the State of California Contractor Directory to find a contractor near you. All the contractors in this Directory have completed a special FEMA training for seismic retrofits of single-family, wood-framed houses.
Imagine if your home collapsed. What would happen to the people inside? Where would you go to live? With those pictures in your mind, make a commitment to preserve your home with earthquake braces and bolts.
At Inspect.net we’re committed to home safety. Prevention is the best way to keep your home safe. Please feel free to contact me any time at jeff@inspect.net if you have any questions.
