Window
Condensation
By this time
of year the conscientious homeowner has restored their fine old
windows, installed weatherstripping and had new storm windows
installed. A week
later condensation and frost is building up and they cannot see
out the windows.
Jade Mortimer, historic window specialist in
Hawley
,
Massachusetts
says, “we know how this happens--cold dry air hits the exterior
of the storm and warm moist air going out through the primary
window greet one another and condense on the interior of the
storm--it is a natural phenomenon, but it is not the explanation
the homeowner hears with a smile.”
That's right, condensation often develops when you change the way
air and moisture move through a wall/window system. Condensation
is a particular problem when the performance of the windows is
changed without consideration of moisture and air movement
throughout the entire building.
Condensation usually occurs when the interior sash is too loose
allowing warm moist air to pass out into the window space where it
is trapped by an exterior storm that is too tight. It is standard
practice in the construction industry to seal exterior storms as
tightly as possible to building. When condensation is extreme
moisture can accumulate and seep into windows sill and sash joints
causing decay over the long-term. Modern storms are designed with
weep holes to let out liquid water, but enough moisture can remain
to condense on the glass. One potential solution is to ventilate
the space between the primary sash and the storm by install the
storm more loosely.
Jim Ialeggio has made custom windows along traditional lines for
decades in
Shirley
,
Massachusetts
. Jim says, “when I install any storm I make it very
clear…that when an exterior storm is used in an old house, the
space between primary sash and storm MUST have more air from the
outside of the house than air from the inside of the house.” Jim
supports his practical experience by learning from the building
scientists. One study demonstrates, counter intuitively, that the
ventilating an exterior storm to the outside did not measurably
effect the insulating value. Most of the benefit of storms comes
from the air space and blocking the major blast of cold winds, and
not from preventing air infiltration.
I often leave a 1/8” to 1" gap at the bottom of the
exterior storm window, which allows the occasional puff of dry
outside air to breeze up into the window space, absorb moisture
and carry it back outside. Some modern storm windows are made with
sliding strip at the bottom that can be adjusted up and down to
make the gap just wide enough to dispel the moisture without
letting in too much cold air. Traditional wooden storm windows
were sometimes made with screen ventilation holes in the bottom
rail, or could be propped open a bit at the bottom.
David Bosken, of New England Storms, in
Hope
,
Maine
, sees this same condensation solution. He has developed a new
storm window that seals tightly at the top to keep rain water out,
but is spaced slightly away from the window trim at the sides and
up off the sill to allow for ventilation that limits condensation.
Tightening up the primary wooden sash with weatherstripping can
help prevent condensation too, but this must be done with some
caution. These old wooden sashes need a little air filtering past
their edges to keep the wood dry, especially at the lower joints.
I have seen several cases where the weatherstripping was too tight
resulting moisture buildup and decayed wooden joints. The tightest
possible weatherstripping around all the sashes is not always the
best thing to do. These days I am sometimes recommending less or
no weatherstripping, although it is contrary to everything we have
been told by the building industry since the energy crunches of
the 1970s.
Adding a tight fitting interior storm window or air panel can
sometimes control condensation. Just be sure to remove them all at
the end of the winter so the wooden parts of the window can dry
out during the spring, summer and fall.
Condensation can be effective controlled (but sometimes not
eliminated) with individual window treatment and
"commissioning." Consider the entire building when
planning window treatments, and consider what each individual
window needs, rather that automatically doing the same treatment
to all windows. Before any window work, window specialists and
contractors need to advise the building owner that the window work
will change the way air and moisture move through the building and
the wall/window systems. What changes will occur varies greatly
from one building to another, and are not usually well understood
beforehand without costly moisture assessments. This may require a
period of two or three years of "commissioning" when the
condensation effect can be observed and minor or major adjustments
may be needed in how they use and operate the entire building and
in the details of the window work.
In the end, I think we can relax a little when it comes to
condensation. You don’t need new plastic replacement windows,
you just need to learn how your windows work and how to operate
them effectively. If you get a little condensation, simple open up
your storm window a crack to air out the space until it clears. If
you get enough to dribble down the glass or build up thick ice
make sure it can drain out and call a knowledgeable window
specialist to solve the problem.
Jade L.
Mortimer
Heartwood
Building
& Restoration
26 Forget Road
Hawley
,
MA
01339
413.339.4298 phone/fax
866.339.4298 toll free
Jade@Crocker.com
http://www.traditional-building.com/brochure/members/1windowrestoration.shtml
Restoration of historic wood windows, energy efficient upgrades to
wood windows and sash
New England
Storms
David C. Bosken
Hope, ME
04847 76 Jackson Road
Home,
Maine
04847
207 763-4873
nestorms@gwi.net
www.newenglandstorms.com
Wooden storm frames with mortise and tenon joints, removable
screen and glass panels.
Jim Ialeggio
Architectural Detail in Wood
41 Parker Rd.
,
Shirley
,
MA
01464
Ph: 978-425-9026
Fax: 978-425-9026
Email: jimialeggio5@comcast.net
New windows based on traditional designs.
Learn more
about windows at www.HistoricHomeWorks.com
Contact Leeke directly for answers to your questions and
more information on techniques for restoring and maintaining your
historic building. Write to John Leeke, Preservation Consultant at
26 Higgins St.
,
Portland
ME
04103
, 207 773-2306; or by E-mail at johnleeke@HistoricHomeWorks.com
or visit his Internet Web Site at www.HistoricHomeWorks.com.
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Replays:
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