On average, more than 1,000 tornadoes touch down annually in the United States, which has more tornadoes than any other country in the world. Tornadoes have been spotted in every state. But Florida and Tornado Alley, which generally runs through the central states, typically see more tornadoes than any other part of the country.
Tornadoes are usually brief — the average one is on the ground for only five minutes, although some can last for 30 minutes or longer — but they’re capable of causing massive damage. (The most severe storms can generate wind speeds of up to 300 mph.) In the U.S., tornadoes are responsible for an annual average of 80 deaths and 1,500 injuries, with additional deaths and injuries caused by severe storms with high winds.
If you find yourself caught in a tornado or a storm with high winds, your odds of survival greatly increase if you have somewhere safe you can take shelter to avoid being hit with flying debris, or being carried away yourself. This 4-by-8-foot severe-storm cube will help protect you on both counts. (Hurricanes and tropical storms pose their own unique sets of dangers. While this structure can protect you from strong winds and flying debris, it won’t protect you from storm surges, flooding, or torrential rain.) When built correctly, this structure will serve as a safe place for you and your family to hunker down when wind-related storms are on the horizon.
Choose a Location
When choosing a place for your storm shelter, the single most important factor to consider is a solid foundation. Your shelter will only be as secure as the surface to which it’s anchored, and the most secure base is solid concrete. A basement is perfect, because the surrounding concrete walls add an extra layer of protection, and the concrete slab provides a sturdy anchoring surface.
If you don’t have a basement, situate your shelter in a garage, utility space, or unused part of your house with a concrete floor. You can pour a concrete slab and build this structure independent of your house, but this will involve adding a roof and siding — steps not covered here. You can also secure it to an existing wood floor, but, again, the shelter will only be as strong as the surface to which it’s connected.
It’s critical to build the walls as shown. If you’re positioning the shelter against one or two existing walls, you’ll need to build the basic framework and sheathe those walls as shown. Then, gather a few strong friends, and shove and pry the structure into position before finishing it and bolting it to the floor. You’ll need enough open height — preferably 9 feet — to secure the two layers of roof plywood in place. If space is limited, you can shorten the structure, but take into account the height of your door.
Tools and Materials
- 8-foot-long 4×4 (pine or Douglas fir) for wall studs and door braces (32)
- 8-foot-long 2×4 (treated pine) for bottom plates (3)
- 8-foot-long 2×4 (pine) for nailing plates (9)
- 8-foot-long 2×6 (pine) for roof ribbon (3)
- 8-foot-long 4×6 (landscape timber) for roof framing (5)
- 8-foot-long 2×12 for blocking (2)
- 4×8 sheet of 3/4-inch plywood for interior and exterior sheathing (23)
- 32- or 36-inch commercial steel door
- 16D ring-shank nails
- 12D ring-shank nails
- 1-1/2-inch joist hanger nails
- 2-inch construction screws
- 3-inch construction screws
- 11/2-inch screws
- 6-inch screws
- 8-inch concrete anchors
- 18-inch strap brackets (10)
- HTT anchor brackets (7)
- Hurricane ties (30)
- Construction adhesive
From the 8-foot-long 4x4s for wall studs:
- 83-inch-long wall studs (30)
From the 8-foot-long 2x4s for lower bottom plates:
- 46-1/2-inch-long ends (2)
- 86-inch-long sides (2)
From the 8-foot-long 2x4s for nailing plates:
- 39-1/2-inch-long ends for upper bottom nailing plates (2)
- 93-inch-long sides for upper bottom nailing plates (2)
- 39-1/2-inch-long ends for lower top nailing plates (2)
- 93-inch-long sides for lower top nailing plates (2)
- 46-1/2-inch-long ends for upper top nailing plates (2)
- 86-inch-long sides for upper top nailing plates (2)
From the 8-foot-long 2x6s for roof ribbon:
- 93-inch-long sides (2)
- 43-1/2-inch-long ends (2)
From the 8-foot-long 4x6s for roof framing:
- 43-1/2-inch-long roof timbers (9)
4×8 sheets of plywood and 2x12s:
- Cut to size
Build the Walls and Roof
Study the illustrations throughout the article, and note the extensive use of construction adhesive, screws, ring-shank nails, metal fastening plates, concrete anchors, and plywood. Used together, these elements create a safe, solid structure. Don’t skimp on any of them; they work together as a unit to keep you secure. The multiple layers of plywood serve not only as wall sheathing, but also as a structural element and “connective tissue” that further ties all the components together. The shelter is designed to make efficient use of 4×8 sheets of plywood; you can safely decrease the size of the structure, but not increase it.
Begin by positioning the four lowermost treated bottom plates. Next, mark out the stud locations on the upper bottom nailing plates and the lower top nailing plates (see “Stud Frame Layout” illustration below), and spread them apart on the floor. Secure the 4×4 studs to the marks using 16D ring-shank nails; the grooves in the shanks of the nails increase their gripping power. Have your door on hand so you can frame the opening for it.
Build and stand all four walls, nailing them to the upper bottom plates with 12D ring-shank nails. Add the upper top plates using 16D ring-shank nails, overlapping the corners to tie the walls together.
Plumb the walls and install temporary cross-bracing on the interior of the studs. Install the 2×12 blocking flush with the exterior edge of the 4×4 studs, with the centers of the blocks 48 inches off the floor. This will help support the seams in the exterior plywood sheathing.
Secure the 2×6 roof ribbon to the top perimeter of the walls, toenailing the 2x6s to the upper top nailing plates. Position the 4×6 roof timbers every 12 inches — one on top of each 4×4 wall stud — and secure them to the 2×6 roof ribbon with 16D ring-shank nails.
Install the 18-inch metal strapping, every 2 feet, to tie the studs, top plates, 2×6 rim joists, and roof plywood together. Extend each strap 2 inches beyond the top of the rim joist; you’ll later bend these over to nail the first layer of roof plywood securely in place. Use stubby 11/2-inch joist hanger nails for all connections.
Add the double sheathing to the exterior walls of the structure. First, apply construction adhesive to the wall studs, and then secure the plywood horizontally with 2-inch construction screws. Overlap the edges of the plywood in the corners as shown in the “Fastener Details: Top” illustration below. Use construction adhesive and 3-inch construction screws to install the second layer of plywood vertically over the first.
If you’ll be positioning the structure against existing walls, sheathe those walls first, and then push, shove, and pry the structure into its final position. Finish installing the remaining exterior wall sheathing. Attach the first layer of roof sheathing with construction adhesive and 2-inch construction screws, and then bend the metal strapping and nail it down with 11/2-inch joist hanger nails. Then, attach the second layer of roof sheathing with construction adhesive and 3-inch construction screws.
Secure the structure to the concrete slab using HTT heavy-tension ties as shown in the “Fastener Details: Bottom” above. Snug the bracket against a corner wall stud, and use a drill bit to drill through the double bottom plates. Use a hammer, drill, and concrete bit to drill the appropriate-sized bolt hole into the concrete. With the nut threaded onto the bolt, pound the fastener into place, and then tighten the nut until the bracket is tightly holding the two bottom plates to the concrete. Then, nail the upper flange of the HTT bracket into the wall stud. Install one of these in each corner, in the center of the 8-foot-long back wall, and on each side of the door framework.
Install hurricane ties to the top and bottom of every other stud, securing them with joist hanger nails.
Add the Door and Snorkel
The door is the weakest link in this structure, so don’t cut corners. Buy a new or used heavy commercial steel door; make sure it swings inward, which will allow you to open the door even if debris is piled up against the outside of the structure.
Position the door and frame in the opening. Secure it to the surrounding framework with 6-inch screws placed every 12 inches; you may have to drill extra holes. On the hinge side, remove one or two of the shorter screws securing the hinge to the frame and replace them with 6-inch screws. Cut the 3/4-inch plywood for each side of the door. Cut the plywood on the outside of the door to allow for the metal door to close tightly against the stops in the frame. Secure the plywood to both sides of the door using construction adhesive and 1-1/2-inch screws. Install the pulls on each side of the door. Don’t bore holes for deadbolts and doorknobs; they’ll only weaken the structure.
On the interior, install one heavy-duty deadbolt latch directly across from each hinge; in most cases, this will involve three or four sets of hardware. The heavier and longer the deadbolt throws and screws used to secure them, the better. Cut a pair of 4x4s to wedge between the inside of the door and the back wall to further ensure the door won’t blow inward in strong winds; leave them inside the shelter.
Install the optional fresh-air intake snorkel of PVC pipe. If your structure is built extremely tight, and you’ll be in the shelter for an extended period of time, you’ll need it. The snorkel can be located on whichever wall you see fit; the one least likely to be damaged or covered in debris will be best.
Stock the Shelter
Once your shelter is complete, conduct a practice drill so your family knows where to go in the event of a storm, where to find the light for inside the structure, and how to secure the door.
Always keep a well-charged flashlight mounted to the wall just inside the shelter door. You’ll need it for finding and activating the deadbolt latches. Optionally, install a motion sensor LED light. Additionally, hang a survival backpack inside the shelter door, where it’s easy to find. Provisions should include a flashlight, battery radio, water, and first-aid kit.
Storm Safety Resources
Insurance Information Institute
Search for “Facts + Statistics: Tornadoes and Thunderstorms”
National Centers for Environmental Information
Search for “Tornado Alley”
Centers for Disease Control and Prevention
Search for “After a Tornado”
Federal Emergency Management Agency
Search for “Taking Shelter from the Storm”
Spike Carlsen lives, writes, and builds in Stillwater, Minnesota. His latest book, A Walk Around the Block: Squirrels, Sewers, Stoplights, and Other Stuff You See Every Day (But Know Nothing About), will be available through Harper One in fall 2020.