Do you remember where you were when the Loma Prieta earthquake hit? I do, I was sitting with my brothers and sisters at the dinner table doing homework. I remember my Mom’s panicked voice as she shouted at us to get out of the house when the shaking didn’t abate after a few moments. I remember being worried about my Dad as he was across the Valley on and evening appointment.
Here in California, the earth moves. It’s a reality we live with every day. Sometimes it’s a fun little ride, and sometimes it’s much more serious. As a building designer I deal with earthquakes literally, every day. People live in the homes we design; this is a great responsibility and we take it very seriously. We can’t predict a large earthquake, but we know one is coming, it’s just a matter of when and how severe.
A shear wall is simply a segment of wall that is designed to resist lateral motion/ force (shear), such as those caused by an earthquake or high winds. In residential construction, we usually accomplish this by attaching sheathing (plywood) to one or both sides of the wall, attached with a specific nailing pattern. We also attach these walls directly to foundations with bolts. Now you may be asking, why isn’t every exterior wall a shear wall then? Ok, perhaps not, but I’ll answer anyway. The answer is, they usually are, at least out here in California.
For our part, it has been a standard practice since the founding of our company to sheath the entire exterior of any new home or addition we design with plywood or more recently OSB. I can’t say that we’ve studied the results, but I’ll bet through the years this has saved our clients tens of thousands of dollars in repairs and possibly a lot of heartache. In fact, following Loma Prieta, we did not get a single call regarding problems or damage in any of our projects.
To distill all of this into one thought: If you have been in a building during an earthquake, shear walls may well have saved your life.