Crawl Space Vapor Barriers
Throughout the Country, even in desert areas, there
is moisture in the ground from groundwater being
absorbed. Even in an apparently dry crawl space, a large
amount of water is entering. The moisture is drying out
as fast as it is entering, which causes high moisture levels
in the crawl space and elsewhere in the house. A solid
vapor barrier is recommended in all crawl spaces and
should be required if moisture problems exist. This
vapor barrier, if properly installed, also reduces the
infiltration of radon gas. Of course, if the moisture is
coming from above ground, a vapor barrier will collect
and hold the moisture. Therefore, any source of moisture
must be found and eliminated. The source may be as
obvious as sweating pipes, or may be more difficult to
spot, such as condensation on surfaces. The solution can
be as simple as applying insulation to exposed sections of
the piping or complex enough to require power exhaust
fans and the addition of insulation and vapor barriers.
The more common causes of moisture problems in a new
home are moisture trapped within the structure during
construction and a continuing source of excess moisture
from the basement, crawl space, or slab. To resolve this
potential problem, 6-mil plastic sheets should be laid as
vapor barriers over the entire crawl space floor. The sheets
should overlap each other by at least 6 inches and should
be taped in place. The plastic should extend up the
perimeter walls by about 6 inches. The plastic sheets
should be attached to the interior walls of the crawl space
with mastic or batten strips. All of the perimeter walls
should be insulated, and insulation should be between the
joists at the top of the walls. Vents, which may need to be
opened in the late spring and closed in the fall, should
not be blocked. If not properly managed, moisture
originating in the crawl space can cause problems with
wood flooring and create many biologic threats to health
and property. A properly placed vapor barrier can prevent
or reduce problem moisture from entering the home.
Vapor Barriers for Concrete Slab Homes
Strip flooring and related products should be protected
from moisture migration by a slab. Proper on-grade or
above-grade construction requires that a vapor barrier be placed beneath the slab. Moisture tests should be done to
determine the suitability of the slab before installing
wood products. A vapor barrier equivalent to 4- or 6-mil
polyethylene should be installed on top of the slab to further
protect the wood products and the residents of the home.
Wall and Ceiling Vapor Barriers
Wall and ceiling vapor barriers should go on the heated
side of the insulation and are necessary in cold climates.
Water vapor flows from areas of high pressure (indoors in
winter) through the wall to an area of low pressure
(outdoors in winter). People and their pets produce
amazing quantities of water vapor by breathing. Additional
moisture in considerable quantities is created in the home
from everyday activities such as washing clothes, cooking,
and personal hygiene. The purpose of the vapor barrier is
to prevent this moisture from entering the wall and freezing,
then draining, causing damage. In addition, wet insulation has
very little insulating value. Insulation with the vapor
barrier misplaced will allow the vapor to condense in the
insulation and then freeze. In cold climates, this ice can
actually build up all winter and run out on the floor in
the spring. Such moisture buildup blisters paint, rots
sheathing, and destroys the insulating value of insulation. |