Exploratory Study of Basement Moisture During Operation of ASD Radon Control Systems
Authored by:Bradley Turk and Jack Hughes
Abstract:The technique most commonly used to control radon in buildings, active soil
depressurization (ASD), has been investigated for its impact on basement moisture levels and
ventilation. As part of an exploratory study, three houses near Harrisburg, Pennsylvania have
been intensively monitored over an 18-month period for moisture indicators, radon levels,
building operations, and other environmental parameters while ASD systems were cycled on and
off. To implement this intensive monitoring program, novel protocols and study design were
developed. A conceptual model suggested that the ASD systems can cause important changes in
basement ventilation and interzonal air flows – therefore these parameters were periodically
measured. Moisture levels were measured in walls and slab floors, indoor and outdoor air,
surrounding soil, and wood framing members in the basement. The participating houses have
unfinished basements: one having poured foundation walls, and the others having foundation
walls of open and partially-filled concrete block. Results from these three houses indicate that
ASD operation can produce significant moisture reductions in the basement air and walls,
especially during non-summer months, and caused the predicted changes in air flow patterns.
Both high and more typical flow and pressure configurations show this effect, although moisture
reductions tend to be greater at higher system flows and pressures. Moisture reductions were
diminished somewhat during the warm and humid summer months. Due to the long response
time of moisture levels in foundation and soil materials, continuous operation of the ASD
systems may cause greater reductions. The findings are consistent with anecdotal reports of
drying and odor improvement in basements during ASD operation, and suggest that microbial
growth may also be reduced. These effects may be different in other climates and house
construction types.
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