Size of storm shelter
I’m putting a storm shelter in my garage/workshop. I originally had it drawn out as 12.75′ x 7.75′, which is 99 square feet. Our family has four people and a small dog. It occurred to me this was oversized, and a waste of precious floor space, so I reduced it to 6′ x 10′, which allows about 10 square feet per occupant, leaving another 10 square feet for storage of emergency items.
Then I thought about it some more, and I should probably be accounting for more than our current family size. Years from now, my wife and I might be living in that workshop, and one of our kids will have a family in the house. So now I’m wondering if I went too small. I tried searching online for size of storm shelters, and saw some pre-built options that were sized based on 3 square feet per person. That seems insanely crowded to me, so I discount that as any kind of benchmark.
Am I overthinking it? Would 2-3 days in a worst case scenario in a 6×10 storm shelter with 8 people be intolerable, bearing in mind this scenario is likely never to play out?
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What kinds of storms are you planning for? Tornados or hurricanes move by relatively quickly and 3sf/person is probably fine. For a nuclear war, I'd want something at least the size of a small RV.
Definitely not planning to hunker down in there for a nuclear war.
I had read that tornadoes are short duration, but hurricanes could be 24 hours+. Aside from that, if the building collapses around the shelter, it might be a long wait to get dug out.
Maybe compare it to sitting in an airplane, which is roughly 6sf/person, plus an aisle space to move around and for pets. For 8 people that might be 8x10 or so, interior dimensions. You could survive in a smaller space but the claustrophobia could be annoying.
FYI FEMA P-320 recommends 7sqft/person for safe rooms intended for hurricanes. 3sq/person for tornadoes.
Something to think about that I had overlooked early on in my shelter planning...
If you plan to frame out the inside/put up drywall, add electrical, etc, make sure to account for space needed for that additional framing (assuming you're doing pource concrete or CMU block for the walls of the shelter). Unless you're going with pressure treated wood you'll need an air gap between the framing and walls as well.
Finished interior dimensions on ours ended up being ~4.5'x7.5' for two adults and a dog. With the (inward) swing of the door it works and we can be comfortable, but 6'x8' interior dimensions would have been far better.
My sense is 6x10 interior dimensions would probably comfortably work for 4ppl + dog. I don't think anyone would complain about extra space if you went 8x10, which also leaves more room for storing supplies (water, food, first aid kit, chairs, bucket for bathroom, etc). <-- Edit: just saw you already mentioned allocating space for supplies
Don't forget about ventilation! FEMA has good documents on building storm shelters, space and ventilation requirements (And approaches), etc.