Wood basement as tornado shelter?
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With all the recent severe weather in the mid west, lots of attention has been directed toward building in some form of shelter. I;m leaning toward a PWF (Permanent Wood Foundation) for both cost and thermal performance reasons. Would a PWF basement provide a suitable “safe room” or would it be advisable to build a shelter, within the basement, out of CMU or even poured concrete?
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Replies
Better: a proper house, safe and bankable.
Instead of a WW trench.
Jerry,
A basement is not a safe room. Even a basement with CMU walls or poured concrete walls is not a safe room. If you want a safe room, you need to follow the specifications for a safe room.
Here are some articles on safe rooms to get you started:
Information published by the Federal Emergency Management Agency (FEMA) about safe rooms
A free article from JLC about code requirements for safe rooms
Martin,
THANK YOU! The FEMA information is most useful and should enable a high degree of survivability. But it seems a builder calling anything a "safe room" or "storm shelter" is seriously limited by the newest codes as it must be tested and "approved". My reading suggests a key difference in a proper basement survival area (can;t say "safe room") is an independent ceiling of reinforced concrete or using plywood and steel plates. Other aspects include a very strong steel reinforced door with multiple deadbolt closures. It appears that by using steel plates, a wooden structure can be made survivable. Putting the :"survival area" in the basement, even if the basement is PWF reduces the exposure thereby increasing survivability but all sides must be "bullet proof".
.
Jerry -
Some discussion of safe rooms under the thread I started here, "Advice for rebuilding in central Oklahoma?". In the end, it comes down to how much extra you want to spend for a better building, extra protection, etc.. Maybe there are better places to save?
I can't imagine any foundation of wood being 'permanent'; and don't like the details I see claiming to be PWF. And basements can flood; and wood can catch fire, as we saw in the OK tornadoes/thunderstorms (pipes break; gas lines rupture, etc.).
A strong ceiling is critical; a woman lost her leg in a tornado when a steel beam fell to where she was sheltering in the corner of a basement. Needs to be strong enough to not lift away or cave in when struck with flying objects (incl. vehicles...). Some of the FEMA details show the safe room ceiling separate from the floor joists above; this may be assuming retrofit, but also should reduce forces being transferred to the safe room structure. True safe rooms should also have carefully designed drainage / ventilation...?
A concrete safe room in the corner is half basement wall anyway...two for one...what zone are you and what's your frost line? Could a partial basement or frost protected shallow footing save enough to go into strengthening elsewhere?