1 November 1996
properly designed sub-soil drainage system will remove radon from sites with severe ground water
(3) Passive Suction Stack, Letter Code E. Extend non-perforated PVC pipe suction stack through
the roof with as few changes in direction as possible. Passive stacks are more effective in colder climates
and during winter months than during warm weather. During warm weather they will be most effective in
naturally ventilated, non air conditioned buildings.
(4) Active Suction Stack, Letter Code F. Extend the suction stack as described above for the
passive stack and install an exhaust fan near the stack discharge. Preferred location for the exhaust fan is
above the roof. Condensation of moisture in soil gases will be minimized if the fan is located in a heated
space, however, any air leakage that may occur at the fan discharge connection will blow concentrated
radon into the building. Any air leakage at the fan intake connection will reduce the suction in the stack.
(5) Design of Sub-Slab Suction System. Pipe sizing for the suction system should be designed
similar to any exhaust system utilizing round duct. The under slab perforated pipe should be no larger than
4-inch diameter. In very large structures, do not increase the pipe diameter in order to increase the length
of pipe runs, this may reduce uniformity in the pressure field. The quantity of air flow in a sub-slab suction
system is effected by a number of variables. The most significant are porosity of the soil, permeability of
the capillary water barrier, and air leakage from the building into the soil. In most locations, the air flow per
1,000 sq. ft. of slab area will be 20 cfm or less. Multiple under slab pipe runs may be cross connected
below the floor using non-perforated pipe of sufficient diameter to maintain uniform pressure in all pipe runs.
Multiple stacks may be connected to a common exhaust fan. Pipes for stacks and any manifolds will be
sized according to air flow and pressure losses due to pipe length and number of turns.
(6) Fan Selection. The fan selected will have cfm and horse power ratings adequate to maintain 1
inch wc static pressure at the slab penetration under constant operation. This will be mounted directly in or
to the vertical riser with air tight connections and will be of such design that condensation of soil gas
moisture will drain either back down the stack or onto the roof. Fans may be an in-line configuration and
installed in the stack or a standard curb mounted exhaust fan.
(7) Naturally Ventilated Buildings. Naturally ventilated buildings that are neither heated or cooled by
mechanical systems and are in any of the facility priorities 1 through 4 will be designed to include passive
barriers (letter code A) only.
b. Existing Buildings. Radon mitigation requirements incorporated into the design of building alterations
will be based upon the facility priority and actual radon measurements in the building. The
design-requirements in table 1 will be evaluated according to life cycle cost/benefit analysis and engineering
judgment. For example, removal of slab-on-grade floors to install a sub-slab suction system may not be
cost effective when compared to the differential in equipment and operating-costs to increase interior air
pressure or the outside-air exchange rate. EPA publication 402-R-93-078 provides guidelines to ensure
10. POST CONSTRUCTION RADON MEASURE.
a. After completion of construction, indoor radon measurements will be made with all HVAC systems
operating on normal cycles. Radon detectors and laboratory analytical services will be obtained through
suppliers that are currently certified under EPA's Radon Measurement Proficiency program.
b. The severity of potential indoor radon concentration cannot be accurately predicted. The time
duration for post construction radon measurement(s) and the extent of mitigation work that may be required
is not quantifiable for inclusion in construction contracts. Therefore, the installation or user agency will be
responsible for post construction radon measurement and mitigation.