Expanding the Use of Concrete Masonry Units in Tornado Safe Room Construction

By Dennis W. Graber

This figure shows the recommended FEMA detail for a safe room in an exsisting home using a thickened slab. The research program will develop more cost-effective recommendations and details.

The NCMA Foundation has awarded a grant to Dr. Craig Baltimore, associated with Kansas State University, for research to provide codes and standards data for more economical construction of in-residence tornado shelters in existing homes. The NCMA Foundation grant funded half of the project cost and the other half was raised locally. The research will provide:

A design for an eccentric footing to allow a tornado shelter wall to be constructed adjacent to an existing wall and
A design for doweling directly into an existing floor slab without having to construct a special foundation for the shelter walls. This will be accomplished through a finite element analysis program using FEMA criteria.

The information obtained will be applicable to hurricane shelters as well. A report summarizing the results and engineering drawings will be prepared and submitted to FEMA for inclusion in their Publication 320. It will also be included in NCMA's Tornado and Hurricane Shelter publication, anticipated for completion this year.

With an above average number of tornado catastrophes in the last several years, more and more residents are considering building a tornado shelter. One of the current obstacles is the large investment required. With having to remove portions of an existing basement floor slab and construct a special foundation, costs are in the neighborhood of $3,000 for an 8-ft. by 8-ft. shelter. The designs will substantially lower the cost of in-residence shelters, make them more affordable, and encourage more people to build them.

Although this information will apply principally to construction of shelters in existing homes, it could establish concrete masonry as the material of choice for tornado/hurricane in-residence shelters and lead to construction of more new homes out of concrete masonry.