Used in this document to refer to the flow of ASD exhaust gases back into the house after they have been discharged outdoors. Re-entrained exhaust can prevent indoor radon concentrations from being reduced to the extent that would otherwise be possible by the ASD system. Discharge of the ASD exhaust above the house eave, and away from openings in t [..]

A parameter determined from blower door testing, giving a measure of the tightness of the house shell. Conceptually, this leakage area reflects the square inches of open area through the house shell, through which air can infiltrate or exfiltrate.

ADD DEFINITION

Stone, crushed stone or other inert material having hard, strong, durable pieces. When used in house construction, it forms the uppermost surface on which the slab is poured, just below the vapor barrier.

The number of times within one hour that the volume of air inside a house would nominally be replaced, given the rate at which outdoor air is infiltrating the house. If a house has one ACH, it means that all of the air in the house will be nominally replaced in a one-hour period.

The rate at which indoor air is replaced with outdoor air; commonly expressed in terms of air changes per hour. AIR PRESSURE DIFFERENTIALS

As used here, a device which gives a visual or auditory signal (e.g., a light or buzzer) when the suction or air flow in an Active Soil Depressurization system moves outside the acceptable operating range for that system. An alarm may or may not also include a gauge to provide a reading of the actual suction or airflow in the system. BACKDRAFTING

Test to evaluate the existence of, or the potential for, backdrafting of natural draft combustion appliances. Published procedures for conducting backdrafting tests are covered in the EPA guide to installation of radon mitigation . Backdraft Testing Procedure:

A semi-rigid foam material resembling a rope of various diameters used to fill around pipes etc., to assist in making a sealed penetration. For example, where a pipe is inserted through a concrete slab, a length of backer rod is jammed into the opening around the pipe. Caulking is then applied to the space above the backer rod and between the outsi [..]

Background measurements are made with instruments exposed to very low radon concentration environments (outdoor air), or can be “blanks”, unexposed passive detectors. Background levels are subtracted from samples before calculating sample concentrations.