Poured reinforced concrete, fiberglass, wood and steel and welded solid steel are materials used in the construction of above ground storm shelters. For the ceilings and walls of wood and steel shelters, the framing is constructed of doubled 2-inch by 4-inch studs, fastened together by 10d nails placed at six-inch intervals. Fourteen-gauge steel sheathing tops two layers of 3/4-inch plywood, all fastened to the framing with 3-inch self-tapping or deck screws, also placed 6 inches apart.
A steel-framed steel door with three deadbolts and 4-inch heavy duty five-knuckled hinges completes the shelter design. When determining where to place an above ground storm shelter or safe room, the ground floor or basement offer more protection than upper floors. There should be no power lines directly below or above the shelter. The garage is often a good location for an above ground shelter as it may offer more room for the shelter than somewhere in the house. Basements, having the benefit of a pre-existing layer of concrete walls, are also a good option.
Five square feet of shelter space per person is recommended for tornado shelters, while for hurricane shelters, 10 square feet per person is ideal. Accordingly, a shelter that is six feet by six feet in size accommodates six or seven people for tornadoes and three for hurricanes.
FEMA's publication, FEMA P-320, includes shelter construction details for different types of shelters and construction materials.