[Greenbuilding] Airtight windows

[Peter Kidd]

OK but Corwyn gave a fairly complete explanation of what problem you 
have to solve, one likely fix but also indirectly suggestions about what 
else you can do.. The recommended RH of 40 - 60 is not realistic during 
the winters of truly cold climates unless you either tolerate 
condensation and icing or have much higher performance windows than your 
9 yr old Pellas. You find interior storms to be out of reach (time and 
effort at least, all 50?) and you don't want to, say, stick strips of 
foam along the bottom of your glazing (I'm not recommending that), but 
somehow lowering the RH or warming the glass (I'm imagining 50 fans to 
boost local temperatures at the glass), are your options as Corwyn 
rightly suggests.

Condensation on the base on the inside is the classic location where 
windows tend to be coldest whether or not they are airtight. The 
airtightness between the panes is relevant to condensation on the 
exterior panes, relatively moist interior air getting to those colder 
outside surfaces. The airtightness of the window assembly can make the 
interior surfaces of a window colder, not just at the bottom edge of the 
glass. Windows will be colder than most other surfaces of your building 
envelope (or hopefully so!!) so windows will be your dehumidifier.

> thanks for the suggestion Corwyn but we have about 50 windows in this 
> house, all of them 9 year old Pellas (the only manufacturer who would 
> make my custom sized windows within my time frame--a long story 
> here).  I can't possibly imagine building storms for the inside of these.
>
> Our indoor humidity is within the suggested range.
>
> S
>
> On Sun, Oct 28, 2012 at 5:24 PM, Corwyn <corwyn at midcoast.com 
> <mailto:corwyn at midcoast.com>> wrote:
>
>     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 <mailto:topher at greenfret.com>
>     (207) 882-7652 <tel:%28207%29%20882-7652>
>
>
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>
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