Perforated pipes shall be of a material approved by the governing local building code for foundation drainage, and sized according to the air-flow estimated from the large-building active soil-depressurization model. Where perforated pipes are installed in gravel meeting ASTM D448, numbers 4 or 5 gravel, with not more than 5 percent passing a 3/8 inch (10 mm) screen.
Perforated pipe pressure distribution manifolds shall be installed only after the installation of all other utilities has been completed and immediately prior to the soil gas-retarder membrane. Pipes shall be installed with a row of perforations located at the bottom of the pipe in order to allow condensate to drain from the system. Pipes shall be arranged in a pattern that provides at least two possible flow paths from any point in the system to a radon vent pipe. Separate sections of pipe shall be solvent welded or mechanically fastened together.