18.13 If you buy or already own a home

If you own your home, you can build a level 2 shelter. The official reference is FEMA guide P-320, Taking Shelter from the Storm (residential safe rooms), and P-361 (community safe rooms and design criteria); both are based on the ICC 500 standard.

What FEMA means by a safe room

• Designed for tornado winds of 250 mph (400 km/h) and to resist the impact of a 15 lb (6.8 kg) wooden 2 × 4 traveling at 100 mph (160 km/h).
• Minimum space: 3 ft² (0.28 m²) per person for a tornado; 7 ft² (0.65 m²) for a hurricane. For your household, your pets, and supplies, plan for considerably more than the minimum.
• Locations: an interior room (closet, bathroom, or storage room with a single door and no windows) built as a safe room; one under the garage floor; or an exterior one, no more than 150 feet (46 m) of travel distance from the house.
• The plans must be signed and sealed by a registered design professional (engineer or architect), unless you buy a prefabricated room certified and labeled to ICC 500.
• Most existing foundation slabs are not designed for the loads of a safe room; an engineer must verify the anchoring.
• Never in a floodway. In flood zones, the floor must sit above the elevation set by FEMA. Flash floods don't always appear on maps: ask your local authorities.

A safe room that also works against fallout

FEMA P-320 does not design safe rooms for radiation, but a reinforced concrete room has mass. With the half-value thicknesses in chapter 15, an 8 in (20 cm) concrete wall equals about three half-value thicknesses: the radiation coming through that wall drops to about 1/10. The roof counts as much or more, because fallout settles on top. If you want dual use, ask the engineer for:

• Concrete walls and roof slab (not just steel panels), with the greatest reasonable thickness.
• A central location in the house or under the garage, as far as possible from the roof and the exterior walls.
• An entrance with a bend, or a shield wall in front of the door.
• Ventilation you can close off and, if possible, filtered ventilation with a battery-powered fan.
• Space for 2 weeks of water, sanitation, and power (chapter 2).

Standby generator, power, and water

• Standby generator running on natural gas or propane: installed by a licensed electrician, with a transfer switch and a permit. Never plug a portable generator into a home outlet: it can electrocute utility line workers. Keep the distance from windows and doors that the manufacturer requires because of carbon monoxide (chapter 9).
• Home batteries with solar panels: quiet and fume-free; ask your electric or gas company about interconnection requirements.
• Storage: pantry and water in a cool room, inside the air-conditioned space, never in the attic or the garage in summer (chapters 2 and 22).
• Water: drinking water storage tanks; rainwater collection (for irrigation and the bathroom, purified if you drink it; chapter 3); know where your home's main shutoff valve is.