Dear
Inspector,
This
month I will discuss some new thinking with regards to crawlspaces
you may be seeing soon. This system seems to be most popular
in the southern US, particularly hot and humid climates.
Most
of us are very familiar with ventilated crawlspaces. This
system allows exterior air, whatever its condition (hot
and humid or freezing cold), into the space through the
ventilation openings. New thinking is: why allow hot humid
air into the crawlspace in summer to possibly condense on
the cooler framing (occupants are typically operating air-conditioning
all summer) and cause damage? Why allow that cold air into
the space during winter to extract warmth from the house,
and even freeze pipes?
Many
new homes are being equipped with pressurized crawlspaces.
Note I did not say conditioned (why heat and cool non-habitable
space?). Here's how it looks; there are no ventilation openings
(obviously). The vapor retarder (plastic sheeting) is carefully
placed on the soil, the laps taped and the edges wrapped
up the foundation stemwall and terminated with a bar or
plastic barbed fasteners. Sometimes the foundation interior
wall is insulated. The underfloor is insulated as usual.
Somewhere in the supply ductwork there is a (sometimes more
than one) small register (two or three inch, similar to
those seen in high pressure forced air systems). There is
no return. The output air from this small opening in the
supply will pressurize the crawlspace just enough to keep
out the exterior air, thus preventing the detrimental effects
of that air. If a return is installed the space is no longer
pressurized and the occupants are spending energy dollars
to condition non-habitable space. The additional energy
cost of a small supply opening is insignificant.
I
personally think this system is great. Some of the added
benefits are: less dust and general debris in the crawlspace
due to no ventilation openings, fewer unwanted creatures
due to less openings (there are always some openings),
and of course less chance of frozen systems in cold weather
and excess moisture in hot, humid weather.
Mike
Casey
Kaplan Professional Schools
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