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Sub Slab Systems
The structure of the home tends to act as natural vacuum. It creates
a strong negative pressure zone on the soil beneath and around the home.
It draws air in at the lower levels of the structure and forces air
out at the upper levels. Your home is virtually breathing in and out
continuously.
A certain percentage of the air drawn into the structure to make up
for the air exiting from the upper levels, the make
up air, is actually pulled in from the soil beneath the
home. It is estimated that as much as 10% of the modern home's make
up air comes from the soil. That percentage of the makeup air creates
a real problem for the indoor air quality
 The
makeup air that is pulled
from the soil brings with it a number of contaminants. In addition to
the radon gas the sub slab air contains bacteria, molds, fungal spores,
and water vapors which can induce mold growth and contribute to odors.
It is with this sub slab air that
radon is drawn to the interior of the structure. Because radon
is a gas a it will easily infiltrate through tiny openings which have
direct contact with the soil, and since it is an atom it will move through
any man made material driven by the force of diffusion.
Consequently, you can not seal
radon or other soil gases out. In their atomic form
the gases are too small to be completely blocked by barriers. Proper
and conscientious sealing may slow the rate of infiltration but it can
never completely stop it. Sump pits, floor drains, utility piping, even
some cracks in the floor become the inevitable pathways through which
soil gases and vapors escape into the atmosphere. The purpose of a proper
mitigation is to see that these contaminants do not remain in the home.
The word " mitigation"
come from a latin root word that means "to lead".
This is what a properly installed mitigation does - it leads the soil
gases through the structure and eliminates the entry into the living
envelope. Since it is impossible to prevent the soil gas
from escaping into the atmosphere, a soil depressurization system uses
a vacuum system to capture the Sub slab air
and guide the gases from the soil to a discharge stack outside of the
home. .
The final design of this system is going to depend on three major
factors:
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