// CODE SNIPPET
Chapter C6 Soil Depressurization Systems
JUMP TO FULL CODE CHAPTER
This chapter provides minimum design and construction criteria for active soil depressurization systems. The operating soil depressurization system shall maintain under the building a pressure less than the indoor air pressure. Systems for buildings with slab on grade floors shall as a minimum comply with Section C603.1. Systems for buildings with off grade floors shall as minimum comply with Section C603.2 or C604.
Suction shall be provided by a fan, rated for continuous operation and having thermal overload with automatic reset features.
The suction fan shall be designed and manufactured to provide an air-tight seal between the inlet and outlet ducts and the fan housing. The fan housing must remain air-tight at air pressure equal to the rated maximum operating pressure.
Electrical power shall be supplied to the fan in compliance with the provisions of Chapter 27 of the Florida Building Code, Building and any additional local regulations.
The soil depressurization system shall include a system monitoring device which shall be either a visual device, conveniently visible to building occupants, or a device that produces a minimum 60 db audible signal, activated by the loss of pressure or flow in the vent pipe.
Piping material shall be of any type approved by locally adopted codes for plumbing vents.
The vent piping shall have a minimum slope of 1/8 inch (3.2 mm) per foot in order to drain any condensation back to soil beneath the soil gas retarder. The system shall be designed and installed so that no portion will allow the excess accumulation of condensation.
Within the practical limits posed by the building, suction points shall be distributed as nearly equally as possible, and as follows:
Suction pipe should be of a size appropriate to the air-flows of the system, a minimum of 1/2 inches (38 mm) in diameter at the fan, and shall not be reduced between the fan outlet and the final termination point.
Suction point pits excavated below the slab shall be sized to provide adequate pressure distribution beneath the slab. Dimensions of 22 inches (559 mm) in diameter and 11 inches (279 mm) deep, or excavation of 1 cubic foot (.02832 m3) of soil, shall be presumed to meet this requirement. Further the pit shall be filled with 1 inch (25 mm) size gravel.
Suction fans must be capable of developing minimum flows appropriate to the system at 1 inch water column pressure. Fans producing 100 cubic foot per minute (cfm) (.047 m3/s) at 1-inch water column pressure are presumed to meet this requirement.
Submembrane soil depressurization systems are essentially the same as subslab depressurization systems, but without the cover of a concrete slab. The membrane shall be protected from wind uplift in accordance with locally adopted codes. Systems may be of suction pit or continuous ventilation mat design.
A membrane soil-gas retarder shall consist of a 8 mil or thicker single ply polyethylene sheet or other sheeting material of equal or lower permeability and equal or greater strength. Place sheeting to minimize seams and to cover all of the soil below the building floor. Retarders must provide excellent environmental stress crack resistance, impact strength and high tensile strength including additives to retard polymer oxidation and UV degradation. Where pipes, columns or other objects penetrate the soil-gas retarder, it shall be cut and sealed to the pipe, column or penetration. All seams of the membrane shall be lapped at least 12 inches (305 mm). Punctures or tears in the membrane shall be repaired with the same or compatible material.
Submembrane soil depressurization systems covering sand or other granular soils shall meet the requirements of Section C602.1, with the suction pits filled with 1-inch (25 mm) size gravel which shall be covered by 1/8-inch (3.2 mm) thick steel plate, 16 gage corrugated sheet metal, or equivalent sheets of other termite resistant structural materials, in compliance with existing and applicable codes.
C603.2.4 Depressurization Systems in Sands or Granular Soils With Continuous Ventilation Mat(s) Design
Suction points shall be equally distributed as follows:
Suction pipe shall be a minimum 3-inch (76 mm) diameter and shall be carried full size to the final termination point.
Suction fans must be capable of developing minimum flows of at least 100 cfm (.047 m3/s), at 1-inch water column (.2488 kPa) pressure.
Vents connecting the crawlspace with outside air shall be sized and located as required to provide mitigation of the indoor radon concentration as demonstrated by post-mitigation test, and shall not be equipped with operable louvers or other means for adjustment by building occupants. Where adjustable vents are used, they shall be permanently fixed in the proper adjustment by the mitigation contractor.