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How to Build a Storm Shelter

This Old House plumbing and heating expert Richard Trethewey shows how to pour a massive concrete storm shelter. Read on to also learn more about design considerations and guidelines to keep you safe from the storm.

This video, featuring This Old House plumbing and heating expert Richard Trethewey, shows how to pour a storm shelter inside a garage. Watch as they explain the need to cut away the garage floor and pour an even thicker foundation. You would need to do this if retrofitting a bathroom or closet, as well.

Steps for Building a Storm Shelter

  1. Cut out and remove the concrete slab from the garage floor, and dig down 28 inches.
  2. Build a wooden form around the excavated hole to create the walls and ceiling of the concrete storm shelter.
  3. Install metal rebar throughout the form to reinforce the concrete.
  4. Use a concrete pump to fill the form with small-aggregate concrete.
  5. Vibrate the concrete throughout the pour to eliminate voids and air bubbles.
  6. Smooth the concrete on top of the storm shelter with a steel float.
  7. Allow the concrete to cure for 24 hours, then strip away the wooden form.
  8. Hang a sliding door and then hire an electrician to run power to the storm shelter for lights and outlets.

Considerations for Building a Storm Shelter

Whether you live in a coastal region, prone to tropical storms and hurricanes, or in the Midwest, always on the alert for a tornado to strike, you want a safe place in your house to retreat to during extreme wind events. Many run to an interior room, hoping a space constructed of 2x4s and drywall will protect them from winds that exceed 100 miles per hour. Having a well-constructed, dedicated safe room in your home will provide reliable protection for you and your family, and peace of mind along with it.

A storm shelter or safe room is a hardened structure built to withstand high-velocity winds that accompany tornadoes and hurricanes, and the flying debris they can hurl at you. A safe room constructed in accordance with the International Code Council’s Standard for the Design and Construction of Storm Shelters (ICC 500) should remain standing even when the rest of your home may be flattened or picked up and carried away. ICC 500 is under review and revised requirements are set to be published sometime in 2020. Here we offer some key ideas to consider when constructing your own storm shelter.

A Prefabricated Safe Room

As an alternative to a site-built safe room, prefabricated storm shelters are commercially available—and in some areas, they’re more affordable. A manufactured safe room generally includes everything except the foundation. But even if tested and approved for missile impact and wind pressure, a storm shelter is only as safe as its foundation is strong. Make sure to follow ICC 500 standards when building your foundation.

Basic Safe Room Construction

Whether building a stand-alone storm shelter or retrofitting a safe room in your house, the Federal Emergency Management Association’s (FEMA’s) booklet, Taking Shelter from the Storm: Building a Safe Room for your Home or Small Business (FEMA P-320), covers everything you need to know to follow the ICC 500 standards, and even includes construction plans. Here are some basic guidelines from this publication.

  • Anchor your safe room to a proper foundation for your geographic location. The safe room’s foundation must be separate from the foundation of the rest of the house.
  • Create walls of reinforced concrete. If retrofitting an existing structure, you can reinforce concrete block walls with additional steel and grout.
  • The safe room requires a concrete roof deck.
  • Only use a certified safe room door to achieve adequate protection.
  • Consult with a licensed engineer in your area before starting the building process. Some standards depend on your geographic location.
  • Basement storm shelters are not recommended in areas prone to flooding or for the mobility-challenged.

Size Recommendations for a Safe Room

The size of your storm shelter depends on the type of storms you typically have in your area. For tornadoes, which typically last minutes, three square feet of floor space per person is the minimum requirement. But for areas prone to hurricanes, which can last 24 hours or longer, recommendations vary from 7 to 10 square feet. Keep in mind that space costs money when designing comfort into your safe room.

Retrofitting a Closet or Bathroom

Your safe room doesn’t have to be an empty room waiting for the winds to blow. Any interior room of your house, with only one door and no windows, can be retrofitted to become a storm shelter. However, this is a costlier option than building a safe room as part of your home’s initial build.

Choose a room you can access quickly and easily. Keep it free of clutter or anything that could fall and cause injury or impede quick access. Also, consider the accessibility needs of all members of your family. Because they include water and a toilet, bathrooms are preferred in hurricane-prone areas where you would spend more time in the room.

Building Outside Your Home

To avoid the cost and mess of retrofitting an existing interior room, many homeowners choose to build a freestanding storm shelter outside or adjacent to the home. Viable options include the back or side yard, under a porch roof, or inside the garage.

In a tornado zone, aim to locate the storm shelter within 150 feet of the home’s entrance for quick access. Also, any common components, like adjacent walls or the foundation, must be retrofitted to adhere to ICC 500 standards. The home’s existing exterior walls and garage floor will not provide adequate protection.

Safe Room Doors

You can build the strongest storm shelter in the neighborhood, but if you skimp on the door your work’s been done in vain. Only use a door assembly that carries a label from an approved testing agency and is proven to resist debris impact and extreme wind pressure.

Doors must pass a missile impact test that uses a 15-pound 2x4 traveling at 100 mph. Doors used in tornado zones must undergo a static pressure test, and those used in hurricane zones must pass both static and cyclical pressure tests. Never substitute any of the hardware that comes with the door, as the test results are contingent on the entire assembly. The National Storm Shelter Association maintains a list of members whose products carry their seal of approval for debris impact resistance.

Once you shut the door, you need to be able to see what you’re doing. If you want to wire lights in your safe room, consult with an electrician. But don’t depend on electricity. Power outages are expected during storms. Consider stocking your shelter with emergency essentials, including flashlights and batteries. Also, since your shelter will be airtight, make sure your builder includes ventilation pipes.