[Greenbuilding] doing something about condensation on inside of single pane windows

[LarenCorie]

From: Reuben Deumling <9watts at gmail.com>

> Basement with 2.5" of styrofoam insulation in floor,
> 10.5" of cellulose in walls, 
> 8" of fiberglass batts in ceiling.
> Quite a bit of attention spent on air sealing, door gaskets, etc.

Hi Reuben.

The first thing that strikes me is the extreme imbalance
with all the effort that went into high levels of insulation
that will have a relatively slow payback in your climate,
while ignoring the huge heat losses through those single
glazed windows. For instance. just one 32" x 16" single
glazed window has much heat loss as near 20 lineal
feet of you thick cellulose insulated walls.   You could
cut that by as much as over 60% just adding a second
layer of glazing.   The cost-effectiveness of curing that
huge hole in your insulation is vastly greater than that
of the very high levels of wall insulation. Insulation is
(usually) most cost effective when used in the most
poorly insulated area.  A lack of attention to those
windows is figuratively like a bucket with a hole
in it, or leaving a door ajar.

> temperature dropped to 30F, a lot of condensation
> suddenly appeared on the inside surfaces of my single
> glazed wood windows. The interior temps in the presently
> unheated space remain in the fifties. Relative humidity
> inside has stayed pretty constant around 75%.

     With 50F air and 75% RH, the dew point is 42F.
55F and 75%, DP is 48F. With your single glazing the
interior glass surface will be about 35F, so of course
you have condensation.     With R2 glazing, the interior
surface would have been more like 43+F barely above
the 50F dew point, with the very high interior RH, but
above it, nonetheless.  Triple glazing (9/16"-7/8" air
spaces) would be more in line with the rest of your
insulation, and would further reduce the risks from
excess condensation. But, you really need to address
the high humidity issue (to below 50% in Winter,
which would make it 25% at 70F.  With the 50F
75% the 70F will be 36%, not bad, but it leaves
you with that very high humidity in your basement
and inside your walls.  Dew point and condensation
are not just on your windows. They are also going
on inside your walls, especially if you have not done
anything (foam sheathing) to raise the temperature
of the potential condensation planes.

 > (1) saran wrap trick on the inside of the windows

   Sure.......two layers (or more) are better than one,
and since you probably don't spend a lot of  time in
the cold basement you might just use foam plugs to
insulate them to R7 or higher.

> (2) desiccant stations (Dri-Z-Air)

I am not knowledgeable about that.

> (3) other?

How are you heating you domestic hot water?
A heat pump water heater would dehumidify
the air. Heating the basement would be another
strategy, though it would probably not be very
energy efficient..

 -Laren Corie-
 Natural Solar Building Design and
 Solar Heating/Natural Cooling/Energy
 Efficiency Consultation Since 1975
 www.ThermalAttic.com  (many new
 photos and pages, coming soon)

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