[Greenbuilding] Airtight windows

Corwyn corwyn at midcoast.com
Sun Oct 28 17:24:44 CDT 2012


On 10/28/2012 1:20 PM, Sacie Lambertson wrote:
Our windows are starting to condensate at the base on the
> inside.  Many of you have suggested this is the penalty of winter.
> Isn't there anything I can do about it?

See my previous suggestion for interior storm windows.

Here's the basics of when you will get condensation.  When the dewpoint 
temperature of the inside air is a the same as (or greater than) the 
temperature of the inside surface of the windows (or anything else in 
your house), that surface will condense water.  So in order to avoid 
condensation you need to either lower the dewpoint of the air inside, by 
reducing the humidity, or increase the temperature of the inside surface 
of the windows.

Whether the humidity is too high is a matter of perspective and some 
controversy.  Get a humidity gauge and measure what yours is.  Generally 
somewhere in the 40% - 60% range is recommended, but balance is between 
being too dry (and the dry throat and colds that that produces) and 
being too wet and the mold and mildew (and the allergies that 
aggravates), so decide for yourself.  That said, lowering the humidity 
will reduce the condensation (and vice versa).  One of the things we 
generally see is that as people increase the air tightness of their 
house they need to go from worrying about too low humidity to worrying 
about too high humidity.  At that point, you are probably in the place 
where you will need to have supplemental ventilation (for fresh air 
reasons), and an HRV will take care of the humidity issue.

The other way is to raise the temperature of the glass.  Traditionally 
this was done by putting the central heating output right under the 
windows so that hot air washed over the surface warming it up.  Now, the 
solution is generally to increase the insulation value of the windows. 
The interior storm windows are a cheap way to do this, adding about R-2 
to a window for about $1.50 per square foot (if you make them yourself), 
I make them for around $4.00 per square foot.  Raising the temperature 
of the glass will also increase comfort levels (even at the same air 
temperature.

Thank You Kindly,

Corwyn


-- 
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
http://www.greenfret.com/
topher at greenfret.com
(207) 882-7652




More information about the Greenbuilding mailing list