Earthquake retrofitting 101

I grew up in California,  where earthquakes are reasonably common place; earthquake drills in school de rigeur. California had the reputation for being earthquake country.  And California started addressing earthquake issues in building codes back in my childhood. 

In Oregon, building codes started requiring houses be bolted in foundations in 1976, but it was not until 1994 that Portland adopted a seismic section of the city building code.  Note the difference between bolting foundations and a complete seismic code which addresses  things like sheer walls and securing water heaters.

So here we are in 2014 and not much has changed.  Portland's old houses sit mostly on concrete foundations of varying condition and quality.  Very few, aside from homes constructed after 1976, have been bolted to their foundations.  What has changed is the available knowledge of an impending earthquake; a big one. 

We're also seeing a slowly growing awareness among home inspectors, home owners and home buyers of the value of earthquake retrofitting. 

 This blog is the first in what I'm sure will turn out to be a series of bogs on earthquake retrofitting. Here are a few basics to start you off. 

These are the general requirements for earthquake insurance for single family homes:  1) Bolting of the sill plate and/or floor joists of the structure to the cement foundation.  2) Adding plywood to brace sub-floor wall areas of homes with cripple-wall construction. 3) Attaching the floor joist walls to the first-floor framing of homes with cripple wall construction. and 4) Strapping/anchoring water heaters to resist horizontal displacement.

Given a concrete foundation in reasonable condition can be bolted to the framing for somewhere between $3000 - $7000.  Brick, block, or houses with crumbling foundations can cost much more, between $50,000 to $200,000. Ack!

In the next earthquake blog, I'll talk about precautions one can take, other than retrofitting the structure of the house, to lessen the impact of an earthquake.  Stay tuned.

Oh, and some of the information for this posting came from Steve Gemmell and his company, Earthquake-Tech.