[Greenbuilding] Earthquakes and older houses

[Koehn Chris]

Bob-

I live on Vancouver Island, on top of (I’m told) 13 faults, most related to the Juan de Fuca plate / North American plate subduction zone. Earthquakes are a big deal here, and our building code experienced a significant up-grade vis a vis seismic fitness of new homes in 2012. 
Here are my thoughts about living in an older home, built before we knew about our earthquake risk:

• If you can, check on your sill plate to foundation connections. Some older houses were pretty skimpy on anchor bolts. Simpson makes a bit of hardware that can be used as a retro-fit if drilling and epoxy isn’t practical. Simpson has published a useful guide for seismic retrofit: <http://www.strongtie.com/resources/literature/seismic-retrofit-guide <http://www.strongtie.com/resources/literature/seismic-retrofit-guide>>
• Check for solid blocking between joists. They can help prevent roll-over in a seismic event, when shear is a really big deal.
• New homes have shear walls, old homes, as a rule, don’t. As I’ve been remodelling my home I’ve taken advantage of open stud walls in key areas and added a layer of 1/2” ply, nailed 6” o.c. (the typical shear panel pattern). 1X8 sheathing is not as good as 4X8 sheets of plywood for shear.
• Brick veneer is usually (or sometimes..) attached with ties and will fail during a seismic event. Get over it, and be thankful it most likely won’t cause your house to collapse. 
• Look for other vulnerable structural connections and reinforce with steel & etc. I have a bedroom sitting on beams carried by 6X6 posts. I added angle iron to the post-to-beam connection: it was just toe nailed previously.
• Big walls of glass (not very common in homes of your vintage, but still..) are particularly vulnerable: poor shear load resistance, and high likelihood of injury from breaking.
• Have a look at: <https://en.wikipedia.org/wiki/Seismic_retrofit <https://en.wikipedia.org/wiki/Seismic_retrofit>>  Scroll down to the part where they talk about residential.

Bottom line is that buildings are currently designed- and I think rightly so- to keep folks alive during a seismic event: not to remain intact. 

As an aside, I heard a story on NPR this morning talking about this very subject: <http://www.npr.org/sections/thetwo-way/2016/03/29/472232829/u-s-geology-maps-reveal-areas-vulnerable-to-man-made-quakes <http://www.npr.org/sections/thetwo-way/2016/03/29/472232829/u-s-geology-maps-reveal-areas-vulnerable-to-man-made-quakes>>
Do the *frackers* own any liability for this? Seems to me like they should…

Best,

Chris Koehn
TimberGuides
Vancouver Island, BC


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