BELOWGROUND HOME FALLOUT SHELTER
H-12-1 / November 1983
(Supercedes H-12-1 dated June 1980)
General Information
This family fallout shelter, designed primarily for homes without basements, is a
permanent home shelter to be placed in the yard. It is designed to have a protection
factor of at least 40, which is the minimum standard of protection for public shelters
throughout the United States. This assures that persons inside the shelter will be
protected against radioactive fallout following a nuclear attack, and will also have
protection against earthquakes, hurricanes and tornadoes.
Following are detail drawings of the shelter, which is capable of housing six adults.
It can be built of poured reinforced concrete, precast concrete slabs, or a combination of
concrete blocks and poured concrete. If it is built as detailed with the top near ground
level, the roof slab can be used as an outdoor patio. The shelter is accessible by a
hatch-door and wood stairway. Fresh air is provided by a hand-operated centrifugal blower
and two ventilating pipes that extend above ground level. In areas where there is poor
drainage or where the ground water table is close to the surface, the fourth modification
on page 5 should be used.
Before starting to build the shelter, make certain that the plan conforms to the local
building code. Obtain a building permit if required. If the shelter is to be built by a
local contractor, engage a reliable firm that will do the work properly and offer
protection from any liability or other claims arising from its construction.
GUIDE TO CONTRACTS AND SPECIFICATIONS
It is generally advisable to have a written contract with your contractor, as well as
technical specifications to supplement the drawing. A widely used and convenient contract
form for construction of this size is the AlA Document A 107, "Short Form For Small
Construction Contract-Stipulated Sum, "which is available from the American Institute
of Architects, 1785 Massachusetts Ave., Washington, D. C. 20036. It would be impractical
to write a technical specification to suit every local condition; however, the following
summary of generally accepted construction materials and practices should be a useful
guide.
EXCAVATION
The excavation should have side slopes gradual enough to prevent caving, or appropriate
shoring should be provided. Materials used for backfill and embankment should have debris,
roots and large stones removed before placement. The sub-grade for the floor slab should
be level for ease in placing waterproofing membrane and to provide uniform bearing
conditions for the structure. The area surrounding the patio should be sloped away at a
minimum grade of I inch per 10 feet to provide good drainage.
CONCRETE
For details of concrete construction, the "Building Code Requirements for
Reinforced Concrete (ACI 318 - 71)" should be followed. This publication can be
obtained from the American Concrete Institute, Detroit, Michigan 48219.
WATERPROOFING
Waterproofing specifications may be obtained from the nearest FHA (Federal Housing
Administration) office, or those of a reputable manufacturer of waterproofing materials
may be used.
VENTILATION
The ventilation piping for the shelter should be installed in accordance with the
practices outlined in the "National Plumbing Code (ASA A40.8 - Latest Edition)."
This publication may be secured from the American Society of Mechanical Engineers, New
York, N.Y. 10018. All pipe and fittings shall be galvanized. Suitable ventilating blowers
and roof ventilators are available from many sources of supply. Fabrication details and
consequently the installation requirements will differ for equipment furnished by the
various manufacturers. Positive-displacement blowers having both electric motor and geared
hand-crank drives are available from commercial sources.
OPTIONS
To accommodate additional persons, increase the shelter length 2'-6" for each two
(2) shelter spaces. Do not increase the 9'-4" width.
Electrical service for lighting and outlets may be installed in the shelter from a
separate residence circuit. A branch circuit breaker should be installed inside the
shelter. Additional lighting and outlets may be provided from this circuit for the patio
above.
An electric motor and pulley may be installed to operate the centrifugal hand-crank
blower by virtue of the electrical service option.
Updated May 2001 - © 2001 By Richard A. Fleetwood 
and
![](pixel.gif"){kind=tracking}