Submitted by: agcomm,  Thu Nov 13 11:02:19 1997


                        November 13, 1997
 
Spring Flooding Will Worsen Winter Home Moisture Problems
 
     Moisture that remains in building materials and basements
after spring flooding is likely to aggravate home moisture
problems this winter.
     "As outdoor temperatures cool, above-ground home moisture
problems increase because moisture condenses on cool surfaces,"
notes Ken Hellevang, an agricultural engineer with the North
Dakota State University Extension Service.  "It's common to see
damage to homes from window condensation and mold growth on walls
beginning at this time of the year.  The mold growth can also be
a health hazard because mold spores in the air in large numbers
can trigger allergies and other respiratory problems."
     Hellevang predicts that those problems will be worse than
usual this year because damp basements and moisture-laden
building materials remain from spring flooding.  Typically, the
worst problems occur in new homes because new lumber and building
materials may have a moisture content of 15 percent or more. 
Those materials dry to about 10 percent in the dry environment of
the winter home.
     "Walls that got wet this spring or summer may still be wet
if they weren't opened up and adequately dried," Hellevang notes. 
"Also, moisture vapor will move into the house through concrete
basement walls and the floor if the soil is wet." 
     The best remedy for home moisture problems is to try to
maintain relative humidity at 30 to 40 percent, Hellevang says.
Lower humidity levels dry out nasal tissue, skin and furniture.
Higher humidity levels increase the chance of moisture damage to
the building and for mold growth.
     Moisture condenses on single-glazed (one sheet of glass)
windows at 30 F if the inside temperature is 70 F and the
relative humidity is 35 percent. With double-glazed windows,
condensation will form at temperatures below zero. Triple-glazed
windows prevent condensation until outdoor temperatures are about
40 F below zero. Condensation will form at higher temperatures if
air leakage cools the window surface.
     "You can control window condensation by adding storm
windows, another pane of glass or by covering windows with
plastic," Hellevang says. Covering the window with plastic will
normally reduce air leakage and help keep the window even warmer.
     Closing drapes over a window typically causes more
condensation on the window, Hellevang notes. Drapes insulate the
window, cooling the surface, but allow moisture-laden room air to
reach the window. Furniture and other objects near a wall can
have the same effect.
     "That's why closets with outside walls sometimes have mold
growth on the wall," Hellevang says.  "Warm air needs to
circulate behind furniture and onto the outside walls of
closets." 
     Humidity meters can be purchased at hardware and discount
stores but may not be as accurate as psychrometers that are
available through scientific equipment suppliers.  Hellevang says
hardware-store variety meters can give you a general idea of the
moisture in your home and can be calibrated to psychrometers for
more accurate readings.
     There are a number of humidity boosters in your home,
Hellevang notes. Each person contributes about three pints of
water per day while breathing. Each shower with a towel hung to
dry contributes another pint. Houseplants, cooking, drying
building materials and moisture transfer from the soil around the
house all contribute. In a well-sealed house, moisture will
accumulate until there is too much.
     Hellevang notes that some exchange of air from inside the
home with air outside is needed to maintain the relative humidity
in the 30 to 40 percent range. Air exchange removes moisture
because the outside air is drier than air inside. Cold air is
able to hold much less moisture than warm air.  Outside air at 30
F and 90 percent relative humidity has a relative humidity of
only 20 percent when warmed to 70 F. Air at minus10 degrees and
90 percent relative humidity has a relative humidity of 3 percent
when warmed to 70 F.
     Air exchange also improves indoor air quality by removing
fumes and pollutants, he says.
     Air exchange may occur naturally when doors are opened and
through normal infiltration. Operate bathroom fans during showers
and for about 15 minutes or longer at other times if humidity is
a problem, Hellevang advises. It may be necessary to open doors
and windows to achieve the required air exchange to reduce the
moisture level in the house. Both an inlet and an exhaust opening
are required to exchange the air. Air-to-air heat exchangers
provides for air exchange while reducing heat loss.
     "Be careful of providing too much air exchange," he warns. 
"If that happens, the air in the house becomes very dry and
heating costs will increase."
     Hellevang notes that dehumidifiers have limited ability to
control winter house  moisture problems. Dehumidifiers are
designed to remove moisture from air that is warm and at high
relative humidities.  They are very inefficient below about 50-
percent relative humidity.
                              ###
NDSU Agriculture Communication
Source: Ken Hellevang (701) 231-7243
Editor: Tom Jirik (701) 231-9629