The amount of floor area per person that your shelter must provide depends partly on the type of windstorm the shelter is intended to protect you from. Tornadoes are not long-lasting storms, so if you are relying on your shelter only for tornado protection, you will not need to stay in the shelter for a long time. As a result, comfort is not of great concern, and a shelter that provides about 5 square feet of floor area per person will be big enough.
When the shelter is intended to provide protection from storms such as hurricanes, which can last up to 12 hours, the comfort of the occupants should be considered. For this type of shelter, the recommended amount of floor area per person is about 10 square feet. Necessities, such as water and toilet facilities, should be provided. The shelter designs in this booklet are based on a maximum floor area of 64 square feet and a maximum wall length of 8 feet. A shelter of that size used for hurricane protection can accommodate up to six people in reasonable comfort. If you plan to build a shelter with any wall longer than 8 feet, consult a licensed professional engineer or architect.