Home & Garden Columns
Matt, We need to reinforce the cripple walls in our 1906 one-story house. But we live in the Berkeley flats and we are worried about potential flooding. We are not that far above sea level and we don’t think that global warming is a fairy tale.
We don’t want to have to tear out all of this plywood bracing with crowbars after it gets wet. We would prefer to screw on the wood panels so that they are more easily removable. Backer On brand screws for wonderboard installation are nice and thick and coated against moisture which is nice, but I think the longest they make are 1 5/8". Are there any screws which are rated for this use? Or is there a system that uses metal somehow?
What a fascinating letter. I’m not quite sure where to begin. Since you’ve presented a number of eye-opening items, I’d like to see if I can take them, more or less, one at a time.
This marks the first letter I’ve received which has specifically asked me to address the needs of a house that may soon be under water due to global warming. Strangely, this is something I’ve actually discussed with some of my clients in the last few years as I’m also one who considers this a very plausible concern.
Nonetheless, if you’re in Berkeley, it’s not very likely that you’re going to be subject to these issues as the elevation in most of the city is well above 20’ and that’s the projected rise if a number of fairly serious events occur over the next 10-20 years. Therefore, unless you’re in the estuary or the very lowest parts of Berkeley/Albany, I wouldn’t devote too much energy to how this will affect your seismic bracing.
If you’re actually down very close to sea level, you may want to think about what you’re going to do with your property if water starts lapping at your foundation. If this actually occurs, there are a lot of consequences that you might want to take into account including how your sewer is going to perform when it’s flooded. Your electrical panel might pose something of a threat if you have to stand in water to reset a breaker.
You might be faced with some fairly serious settlement if your house is sitting in water and the effects of an earthquake on a house that’s sitting in mud are likely to be quite a bit worse than one that’s sitting on dry land.
Alameda is another matter entirely since much of that fair city is less than 20’ above sea-level, meaning that Alameda might become the Venice of the Bay if the south pole loses a large amount of ice which is hanging on by Al Gore’s fingernails.
Now, there might be an upside to all this water if you look at it the right way. The ferry from S.F could drop you off at Spenger’s. You could stay at home and fish. The Cal Water Polo Team will be able to stage exhibition games in your basement.
But this is probably a very serious concern and were it to actualize. I’d say that your house will no longer be your house. It will be devalued to a degree where it will probably not be a house for anyone anymore. For the time being, I’d eat more chocolate and watch funnier movies. Oh, and reduce your carbon emissions.
As for planning shear-wall sheathing around rising sea-level, I just wouldn’t go there. I’d say that earthquakes are a more tangible eventuality and that you should plan for them without any serious thought toward removal.
If sea-level actually rises to where you live, your whole house is going to be so seriously affected that removal of the shear-wall sheathing probably isn’t going to make it into the day planner for next Tuesday. So just go ahead and do your shear-wall sheathing, bolting and other hardware connections so that you can survive an earthquake.
By the way, if you are actually quite close to the bay, you might just be in a liquefaction zone. It’s a good idea to find out because the shaking forces are much greater in these places and it’s good to plan for this. Houses are more likely to experience serious damage when they’re in liquefaction zones because the earth moves more in these places and also because the earth can rapidly subside.
Now, for the last part of your question; shear-wall sheathing, which is typically assembled using plywood panels and nailed to the framing of the house with a large number of nails is best installed without the use of any sort of screw.
There is apparently one screw which has very recently come on the market and that can be used for shear-walling but, as a rule, screws are a very poor choice because they tend to be quite brittle, while nails have great ductility and can bend many times before they break. The screws you are describing for use on concrete tile-backer board are not going to pass muster. They might be moisture resistant but they don’t have the shear value that’s called for.
Therefore, I would suggest that you abandon your plan for temporary or removable shear-walling. I see too much shear-walling that is so poorly done that I’m worried it won’t do the job when the great moment arrives. So any attempt to short-change the process by making the work removable is just not on the table for me.
In short, here are my suggestions: Retrofit your house, hire the Dutch to put sea doors just outside the Golden Gate, don’t ask the U.S. Army Corps of Engineers to build levees (or anything) in the Berkeley Marina, stop watching An Inconvenient Truth (once for you was quite enough—but get all your friends to see it) and start collecting two of every animal. When you’re ready, call me, I’ve got cats, raccoons, squirrels, skunks and at least two deer.
Stay in touch,