Select the location for the storm shelter. If possible, place the shelter in the center of the basement. Avoid the corners of the basement as it has been found that debris tends to gather in the corners if the house is hit. This makes corners a very bad place to be. Mark out the outer perimeter of the shelter. You can make these shelters as large or small as you desire. For this example we will be constructing an 8-by-8-foot shelter. This would be considered a very large shelter capable of holding an entire family. A large family at that.
Use the hammer-drill to drill 3/8 inch holes into the concrete floor of the basement. Drill holes approximately every 2 feet and to a depth of 3 inches. Adjust these measurements as required to allow for your door and to allow the holes to line up with holes in concrete blocks. Place six 1/2 foot lengths of re-bar into the holes. Once the re-bar is in place, begin your walls by laying out the first layer of concrete blocks. Slide the blocks over the re-bar and interlock the blocks. At the doorway you will need to use half blocks to complete the wall. Continue to stack the blocks up to a height of 6 feet. This will be approximately nine blocks in height. Use the level to make certain the walls are straight and square.
Mix the concrete in a wheelbarrow, keeping the cement slightly runny/wet. Fill a bucket with the wet cement, and poor it into the holes in the concrete blocks. The cement should flow down through the honeycomb and fill the walls completely. Bring the cement to the top of the wall, filling all openings as completely as possible. When the cement dries, it will act as a solid wall, reinforced by the re-bar and concrete blocks. Without the core of cement, the concrete blocks could be shattered by debris propelled by the high winds inside a tornado.
Lay the two pieces of plywood across the top of the walls. The re-bar will be extending up approximately 3 inches above the concrete blocks. Drill holes in the plywood to allow the re-bar to protrude above the top surface of the plywood. This will hold the plywood in place and help secure the roof to the walls when the roof concrete is added. Measure the exact distance from the floor of the new shelter to the plywood. Cut the 4-by-4-inch boards to match this measurement, then insert them in the center of the shelter along the seam of the two pieces of plywood. Place them approximately 2 1/2 feet from each wall and nail them in place from the top of the plywood. Use the 2-by-4-inch boards to construct a frame on top of the plywood. The frame can be either screwed together or nailed together around the outer edge of the plywood. Screws are far easier to remove when it is time to dismantle the frame. Mix additional concrete and fill the frame to a depth of 1 1/2 inches. Crisscross re-bar across the concrete, then add more concrete to bring it to the top of the frame.
Install a metal door in the opening to the shelter. You will need to modify a metal door to the proper height to fit the opening, which in this design is 6 feet in height. Secure the metal door frame into place with masonry screws. Because the doorway will be the shelter's weakest point, you will want to place more screws in the door frame than on a normal door. Space them approximately 8 inches apart around the entire top and side of the doorway.