United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S8-91/208 Nov. 1991
EPA Project Summary
Recommended Sub-slab
Depressurization Systems
Design Standard of the Florida
Radon Research Program
David E. Hintenlang and Charles E. Roessler
The Florida Radon Research Program
(FRRP), sponsored by the U. S. Envi-
ronmental Protection Agency and the
Florida Department of Community Af-
fairs, has developed a technical basis
for the design of sub-slab depressur-
ization systems for the control of ra-
don infiltration into buildings. Results
of the research conducted under the
FRRP are presented in several techni-
cal reports. This report is the support-
ing document for the draft code relat-
ing to sub-slab depressurization. The
design criteria are first presented, fol-
lowed by details of the depressuriza-
tion system.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Tri-
angle Park, NC, to announce key find-
ings of the research project that Is fully
documented in a separate report of the
same title (see Project Report ordering
Information at back).
Introduction
Elevated indoor radon gas generally
comes from radon gas that is formed from
radium in the foundation soils under the
structure. In structures built on a slab, one
of the most effective ways to limit soil gas
entry into the structure is to depressurize
an area below the slab as with an exhaust
fan. The radon thus removed from below
the slab is exhausted into the ambient
atmosphere. This portion of the standard
sets forth the design criteria and the de-
tailed specifications for equipment associ-
ated with sub-slab depressurization.
Soil Depressurization Systems
601.1 Design Criteria
Specifications are set forth for the fol-
lowing design criteria: pressure, fan, and
seal.
601.2 Suction Fans
Each suction fan shall be rated for not
less than 100 cfm air flow at 1 in.* water
column. The soil depressurization system
shall include a system failure alarm which
shall be either a visual device, conve-
niently visible to the building occupants,
or a device that produces a minimum 60
db audible signal, activated by the loss of
pressure, or t'ow, in the vent pipe.
601.3 Vents
Vent piping material shall be of any
type approved by locally adopted codes
for plumbing vents. The piping shall have
a minimum slope of 1/8-in./ft* and the
vent pipes shall be terminated above the
roof at least 10 ft from any operable open-
ings or air intakes and directed away from
any operable openings or air intakes. AH
exposed components of the soil depres-
surization system shall be labeled to pre-
vent accidental damage or misuse.
601.4 Depressurization System
Arrangement for Slabs on Sands
or Granular Soils Without
Continuous Ventilation Mat(s)
Depressurization systems in sands or
other granular soils (certified as having an
air permeability of greater than or equal to
10-1Z m2) at least 8 in. deep shall meet the
* 1 in. H2O = 0.25 kPa; 1 in. = 2.54 cm; 1
ft = 0.30 m.
Printed on Recycled Paper
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specifications set forth in this section. Suc-
tion points shall be equally distributed a
maximum of 1300 feet2* per suction point,
each suction point shall be located not
less than 6 ft or more than 18 feet from
the perimeter, and multiple suction points
shall be located within 36 ft of each other.
Suction pipe shall be a minimum of 2 in.
in diameter and shall be carried full size
through the roof. Suction point pits shall
conform to one of the following designs:
(a) a hemispherical pit at least 22 in. in
diameter and 11 in. deep, with a cover of
1/2 in. minimum thickness pressure-treated
plywood or other decay-resistant material,
installed below the soil-gas barrier; or (b)
a hemispherical pit at least 32 in. in diam-
eter and 16 in. deep filled with 1 in. or
larger washed gravel and covered by the
soil-gas barrier; or (c) a manufactured ven-
tilation mat having a minimum net suction
* 1 ft1 * 0.09 mz; 1 cfm = 0.00047 nV/s.
area in contact with the soil of 5 ft2, in-
stalled below the soil-gas barrier.
601.5 Depressurization Systems
in Sands or Granular Soils with
Continuous Ventilation Mat(s)
Five arrangements are specified for the
suction points. The suction pipe shall be a
minimum of 3 in. diameter and shall be
carried full size through the roof. Suction
fans must be capable of developing mini-
mum flows of at least 100 cfm* at 1 in.
water column pressure. Depressurization
systems in a minimum 6 in. deep layer of
aggregate shall have suction points equally
distributed at the rate of one centrally lo-
cated suction point for every 2500 if of
floor area. Specifications for the aggre-
gate are given. Suction points shall be
connected to the depressurization fan by
a minimum 4 in. diameter riser and shall
terminate in the gravel layer in a "tee"
fitting or other approved means that pro-
vides for air flow from the gravel layer.
602. Membranes Without Slab
Cover
Sub-membrane soil depressurization
systems are essentially the same as sub-
slab depressurization systems, but with-
out the cover of a concrete slab. The
membrane shall be protected from wind
uplift in accordance with locally adopted
codes. The membrane shall consist of an
air-impermeable plastic membrane meet-
ing four specified arrangements which are
outlined. Sub-membrane suction systems
covering a minimum 6 in. deep layer of
aggregate having a 1 in. average diam-
eter stone shall satisfy the requirements
of Section 601.
Supporting information is given for each
of the specifications.
D. Hintenlang said C. Roesslerare with the University of Florida, Gainesville, Fl 32611.
David C. Sanchez is the EPA Project Officer (see below).
The complete report, entitled "Recommended Sub-slab Depressurization Systems
Design Standard of the Fbrida Radon Research Program," (Order No. PB92-
105626 AS; Cost: $17.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Off leer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S8-91/208
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