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Most efficient way to build a storm shelter

Trevor Lambert | Posted in General Questions on

My wife has decided we need a place to go in case of a tornado or hurricane. Our house is a slab-on-grade, so no basement, and the the main floor is very open so not even a good place to hunker down there.

I’ll be building a workshop/garage in the near future, so that’s the obvious place to put it. I can think of two options. One is to excavate and have a partial basement under part of the workshop. The other is to build a reinforced room above grade. It seems to me that the latter option would be cheaper and easier, but I’m really just guessing. One major factor to consider is that we have a high water table; it was 3 feet below grade where we built the house, though it does vary over the whole property. That will make excavating and building below grade more complicated and expensive, not to mention waterproofing the structure.

What’s the general consensus between these two options, and are there any others I haven’t thought of?

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Replies

  1. Expert Member
    Malcolm Taylor | | #1

    Trevor,

    I would think about reinforcing part of the above ground structure so that it could also be used for some other purpose (secure storage? pantry?) as hopefully it is never needed for its primary purpose. That would also let you use the larger building's control layers. Maybe it's a CMU room in one corner?

    You are in southern Ontario aren't you? My MIL's townhouse unit in Barrie was completely flattened by tornado a decade or so ago.

  2. Andrew C | | #2

    In the States, FEMA has developed guidelines for safe rooms. You can find a lot information that may provide food for thought on the topic at their website. https://www.fema dot gov/safe-rooms. Publication FEMA P-361, 3rd edition covers lesson learned wrt residential applications, and dovetails w/ ICC 500, the Standard for the Design and Construction of
    Storm Shelters.

    I like the direction that Malcolm has suggested.

  3. Walter Ahlgrim | | #3

    Given your water table above ground seems the best option.

    I am not sure what you mean by “efficient” cost verse strength. How much strength you want will be the driving factor in cost.

    Have you looked at the prefab units?

    A room in your shop with 2x6 studs wrapped in fence wire and covered in ¾ plywood inside and out would stop most flying objects but is light enough to become airborne.

    A filled concrete block (CMU) wall connected to the slab with rebar would be pretty good.

    The shelter in this thread is the best above ground shelter. A rebar cage with the walls and roof poured together then build a home addition over it
    http://www.owwm.org/viewtopic.php?f=3&t=214508

    Walta

  4. Trevor Lambert | | #4

    Sounds like above ground is the way to go, which is the way I was leaning. I also thought it would need to be engineered, but it sounds like it's simpler than that.

    Malcolm, would that have been the Goderich tornado by any chance? We were camping just down the road from that (in a tent, no less). We were in the warning zone, saw incredibly strong winds and rain and ended up taking shelter in the park centre.

  5. Expert Member
    Rick Evans | | #5

    Trevor,

    Obviously, a subterranean shelter would keep you safe during the strongest of storms (except maybe this one: https://en.wikipedia.org/wiki/1997_Central_Texas_tornado_outbreak ). But you are unlikely to be hit by an EF-4 or EF-5 tornado even if you lived in Oklahoma. These make up less than 1% of all tornados. I am willing to bet that Eastern Canada has never seen an EF-4 in the last 100 years.

    An above ground shelter is the way to go. I would build a room with poured concrete with imbedded, welded wire mesh. If anchored properly, etc, this would certainly keep you alive through the most violent of storms you're likely to face.

    1. Expert Member
      Rick Evans | | #6

      Wow- Just looked it up. Ontario has had no less than 6 EF-4 tornados! I realize it is a massive province, but I think I would want a storm shelter as well.

  6. Expert Member
    Zephyr7 | | #7

    Personally I prefer underground shelters. I’d price that out. If you go underground you just need a block wall (or poured if you want), with no special reinforcement beyond a normal basement wall.

    If you go above grade, I’d use poured walls with rerod and remesh. Look into hurricane rated construction methods for this which specify what to do to stop a flying 2x4. Ideally you want a poured concrete roof too, not a normal wood roof. I would tie the structure into the slab with additional rerod to help the shelter resist wind force better. Use a reinforced steel door with a frame set into the concrete walls. The door needs to be able to withstand the same forces as the wall.

    Make sure you run power and a phone line into the room. I would also recommend installing a battery-backed light in the room. Commercial battery backup ballasts are available that are completely automatic and will give you 90 minutes or more of light on their internal battery. These are better than the old “mount it on the wall” type of backup light. Leave enough space in the shelter for a shelving unit where you can keep some bottled water and maybe a small supply of canned food. You don’t need lots, but enough for a few days in case a storm really trashes your town and you can’t drive around for a few days.

    Bill

    1. Expert Member
      Rick Evans | | #8

      Bill, I was hoping you would leave a reply here. Good stuff, as always!

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