Danger lies in 'soft-story' homes

Q: I have a den above a garage in a soft-story house. I am considering a floor-to-ceiling bookcase and a baby grand piano. The piano will weigh 800 to 1,000 pounds. As for a wall of books, I have no idea how much that would weigh. Do you see the need for some kind of reinforcement so it won't sag the floor, etc.?

A: Putting that much extra weight in the den will stress the framing below, especially on a soft-story structure, which has ground-floor space located where a wall might otherwise be. This makes the building's frame prone to twisting and buckling in an earthquake.

Beefing up the floor joists is a must. You should also install shear panels on the garage walls to provide additional lateral support in the event of an earthquake.

The piano and the books will make the garage section even more top-heavy. Installing shear walls on these walls will give it the best chance to survive a tremor of moderate to severe magnitude.

Your first step is to head down to the local building authority with a plan and secure a permit. Ask the inspectors about joist size and don't be surprised if they require some engineering. It is basically a seismic retrofit, and buying an engineer's report is money well spent.

Identify the joists' thickness, the spacing between them and the length they run without intermediate support in the garage. Check a joist span table to determine the width of joists you might need given the span and the distance between joists. Given the added load of books and piano, we would build beefier -- either with a shorter span or a thicker joist. Span charts can be found in the Uniform Building Code, in any good construction manual or in many places on the Internet.

An alternative is to double up the size of the joists by "sintering" new wood onto the old joists, essentially making 2-by-4s into 4-by-4s. From a retrofit standpoint, it is the best alternative because the new material will fit onto the top plate of the garage, forming a 90-degree angle, allowing the studs to be attached to the joists as part of the shear wall.

Installing shear panels is more than just nailing some plywood to the studs. The goal is to make the foundation, the mudsill, the wall and the floor joists into a monolithic unit by tying these components together. It is accomplished with specialized metal fasteners and a skin of plywood or oriented strand board. ...CONTINUED

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