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- Another area of a house, which must
breathe for its well being, is the basement and crawl space.
- Lack of proper ventilation in a basement
or crawl space is frequently a problem. The use of
 dehumidifiers
during the warm months of the year is beneficial in assisting the
removal of moisture from the air. Circulation of the air also
helps reduce problems, assuming the volume of air being moved is
consistent and sufficient.
- Crawl spaces can add considerable moisture
to a house. A vapor barrier of 4 or 6 mil polyethylene laid over
the earth in the crawl space area with a minimum of joints
(overlap joints a minimum of 24 inches) is generally recommended.
To be effective, vapor barriers must be continuous. Installation of
paper or foil-faced insulation between the floor joists will also retard
infiltration of moisture into the house. The vapor barrier on the
insulation should be placed against the heated side or the subflooring.
If you use single-faced insulation, the exposed insulation should face
the crawl space (fuzzy side down). Insulation with a vapor barrier
facing on both sides is a good option for insulating a crawl space or
basement.
- In the summer months, the outside air will
typically be 15 to 25 degrees warmer than the air in the crawl space.
This will cause the humidity to rise in the crawl space, because warmer
air has more ability to hold water than cooler air. In dryer climates,
this may not be important. In coastal and northern climates, depending
on the conditions in the crawl space, moisture may reach its dew point,
which makes a case for ventilation. With proper ventilation, the
saturating air in the crawl space will be diluted and the relative
humidity controlled. If there is a dirt floor, a polyethylene vapor
barrier should be installed to keep moisture from migrating out of the
soil. A dirt floor should be looked upon as a large evaporator
plate. In the winter months, the outside air will be cooler than
the air in the crawl space. The warmer air in the crawl space will have
more ability to hold water than the cooler outside air. The potential
for condensation is remote at best in colder months, except in some
coastal areas with excessive humidity. Generally, crawl spaces do not
have to be ventilated in the winter, as long as there is no water
penetration from other sources such as negative surface grades, which
could create excessive moisture in the crawl space. Having warmer air in
the crawl space is the key. Ventilating the crawl space is okay in
colder months, however, the living space floors above the crawl space
may be cold, uncomfortable and waste heat, even if they are insulated.
For most climates, the recommendation is to ventilate the crawl space in
the summer and close them in the winter. If there is a basement, a
window or opening should be left open into the crawl space, even if it
allows some heat loss from the basement to the crawl space.
- Exhaust vents (kitchen, bath, dryer, etc.)
should not terminate in a basement or crawl space. They should
terminate to the exterior of the structure.
- The space between the bottom of the floor
joist and the earth under any building (except such space as occupied by
a basement or cellar) should be provided with ventilation openings
through foundation or exterior walls. Ventilation openings require
a net area of ventilation not less than one square foot of clear air for
each 150 square feet of crawl space area. One ventilating opening
must be located within 3 feet of each corner of the building. The total
area of ventilation openings may be reduced to one square foot for each
1500 square feet of under-floor area, when the ground surface has been
covered with a continuous and properly lapped vapor barrier material.
There is still a requirement for one ventilation opening to be located
within 3 feet of each corner of the building. The vents may have
operable louvers. Ventilation openings may be omitted on one side
of the building (generally in the front).
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Condensation Common
Defects Summary
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