We have had more queries about Earth Quake Retrofits since the March Earth Quake and Tsunami struck Japan.
If you live in an old Portland home, the house is likely only sitting on its foundation. Gravity is holding it in place. It is not anchored to the foundation.
If this is the case, your home will probably not do well in a major earthquake, and you probably cannot purchase an earth quake (EQ) rider for your home owner’s insurance policy.
For good detailed illustrations of what earth quake retrofits usually involve, please look at the Simpson Strong-Tie Retrofit Guide and the Portland Bureau of Development Services Residential Seismic Strengthening brochure.
Your insurance company may have a relatively low standard to obtain an EQ rider. Often, they only require that the mudsill (the horizontal piece of wood framing that lies directly on the concrete) be anchored to the foundation.
If you are interested in your house actually surviving an earth quake, you may choose to take further steps, such as installing connectors to tie the rim board to the mudsill or cripple wall (a short wall between the foundation and the floor system), blocking between floor joists, installing sheer panels on cripple walls and interior walls and even augmenting the foundation walls.
All seismic and structural work in Portland requires a building permit. You wouldn’t be able to qualify for an EQ rider without a permit for the new work in any case.
The strength and benefit of the new work is limited by the condition of the members you are tying together. If your foundation is in very poor condition or the mudsill is rotted, they would have to be repaired first. These repairs are often significantly more expensive than the basic retrofit work.
There is currently no building “code” for earth quake retrofit work in Oregon. The building department only ensures that the planned and permitted work has been properly performed.
Who decides how much reinforcement is adequate? One obvious answer is an engineer, but even then the question remains how much. What is the correct standard to engineer to, and what is the right balance between safety and expense?
If you want more than the minimum to obtain an EQ rider, we suggest following the guidelines in the Simpson Strong-Tie Retrofit Guide. Here in Portland, we suggest adding more anchors with one very 4 feet instead of every 6 feet. If your house exceeds the sizes discussed in the guide, we would bring in a structural engineer to evaluate the plans and stamp them.
The cost of retrofit work is going to depend on how many linear feet of foundation wall you have, whether your floor system sits directly on the foundation wall or on a cripple wall, how many posts and footings you have, the condition of the concrete and wood to be worked on, and access to the interior of the foundation wall (does anything need to be removed and then reinstalled to access the work area).
Do check with your insurance agent before starting any work to make sure that your plan will satisfy their requirements.