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Monitoring moisture to control mold
By Dwight Barnett
Scripps Howard News Service
December 16, 2002
Q: I have several questions related to fixing a problem involving moisture and
mold in our home. We have a 12-year-old, one-story brick home with a crawl space
that can be accessed through the attached garage. The home is heated by a gas
furnace. Our house has no gutters, but we have continuous landscaping around the
house consisting of rock and small shrubs and plants. Our windows almost always
have water sitting on the inside sills, and this has resulted in mold growing on
the woodwork.
I have washed the windowsills with an ammonia and TSP solution and it seemed to
get rid of the mold for now. Last week we purchased a 44-pint dehumidifier for
our home to see if it would help. On mornings that are extremely cold, there is
still water on the windows, even if we do not have any curtains or blinds pulled
down. Still, the dehumidifier seems to help somewhat. But it runs constantly and
takes out about 30 pints of moisture during the day and 15 to 20 pints at night.
My husband went under the house, and he said that there was mold growing on the
floor joists in the crawl space. What can we do to stop the mold from growing in
the crawl space? Will venting the crawl space help and how do you go about this?
Can our dehumidifier be placed down there to take care of the house and crawl
space? What can we spray on the wood floor joists to get rid of the existing
mold?
And is it possible to take out too much moisture from your house, and, if so,
how do you know when to stop?
A: The problem can be found in the crawl space. The soils release moisture to
the air under the home all the time. Even during extended dry periods, the
shaded, covered soil gives off moisture. The dirt surface may seem dry to the
touch, but down deep the soils are damp. The dirt under the home needs to be
covered with a plastic vapor barrier. Use a 100-foot long roll of 6-mil plastic
sheeting, which can be found at most home and farm stores.
It does not matter if you use clear or black plastic. What is important is that
100 percent of the dirt floor be covered. Overlap the vapor barrier at joints or
seams by at least six inches, but do not lap the barrier over the foundation
walls. Anchor the plastic to the ground using bricks or stones at the corners
and tape the joints.
The crawl space can then be vented by adding foundation vents at each corner of
the home. Holes are drilled through the brick and the block of the foundation
above the outside grade and landscaping. Next, an 8-inch-by-16-inch area is
removed for each vent. Cutting holes in the foundation is tricky and should be
left to professionals.
You can then dehumidify the crawl space with either a dehumidifier or with a fan
placed near the entrance. After the humidity level has dropped below 60 percent
and the wood has had time to dry, the floor joists need to be inspected for
signs of decay or infestation damage. Damaged wood needs to be replaced with
treated lumber. A licensed pest control operator can treat moldy wood with a
borate such as BoraCare.
Once you get the humidity under control in both the crawl space and the home,
you need to monitor the moisture level of the living areas. Specialty stores and
department stores carry relative-humidity-sensors that record the moisture level
near the instrument.
Monitoring is important because you can take too much moisture from the home,
causing the wood to shrink. That in turn causes doors and windows to stick and
walls to crack. Cracks may also appear in woodwork, wood flooring and wood
furniture.
In a dry environment, static electricity may also become a nuisance. The
moisture level in the home should be maintained at 40 percent to 60 percent for
comfort, wood preservation and to restrict mold growth. Do not be alarmed if you
continue to find moisture in the windows. Even with lower humidity levels, the
windows will continue to sweat because the glass gets so cold. Daily drying and
cleaning of the windows will stop mold growth.
Another source of excess humidity might be the flue on the gas furnace. A
blocked or poorly vented gas appliance can produce gallons of moisture, as well
as noxious gases, every day. Have the flue and the furnace checked annually by
qualified service technician. Install a carbon monoxide alarm for added safety.
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