[Greenbuilding] condensation on storms

RT archilogic at yahoo.ca
Thu Oct 24 14:25:40 CDT 2013


on Wed, 23 Oct 2013 23:39:42 -0400, Benjamin Pratt  
<benjamin.g.pratt at gmail.com> wrote:

>  Although I caulk all my windows with removable caulk every Fall, the
> storms always get quite a bit of condensation on them, especially on the
> top floor in the rooms adjacent to the shower.

Ben;

My parents' century-old home used to have wooden-sash exterior storm  
windows that were put up every Fall and removed every Spring.

On the bottom rail of the sash there four 1.5 - 2 inch holes arranged in a  
pattern  and there was a pivoting flap which could be opened as required.  
As a kid I just assumed that those ventilation holes were to allow fresh  
air into the house if desired. In later years it occurred to me that they  
were to facilitate drying of moisture build-up between the double-hung  
windows and the storms.

About 30 years later when building my own home, I installed Pella [spit!]  
windows because they were considered the best ( but in reality, just the  
best promo literature).

This was back in the days when they offered a removal interior pane which  
clipped into the wooden sash and used compression bulb gaskets to provide  
the air seal.

Unfortunately, the folly of Pella's [spit!] design became apparent the  
first heating season when condensation formed against the inner surface of  
the exterior pane of glass. Pella [spit!] had designed the wooden sash  
with two 3/8" dia holes drilled through each of the four rails, with  
plastic sleeve inserts in each of the holes which could capture a plastic  
ball "plug".

Which of the holes received a plastic ball plug was determined by the  
orientation of the sash.  (ie Awning window sash are casements flipped 90  
degrees).

Some of my windows had fogged up because paper wasps had plugged up the  
ventilation holes with mud.
D'Oh!

You may be too young to remember but there was a time when sealed  
insulating glass units sometimes had a small breather hole drilled through  
the outer pane of glass in an upper corner to allow moisture between the  
panes to cook off.

The point of all of the above ? In the past when window makers  
acknowledged that they had difficulty making a perfect air seal, they  
provided ventilation holes in the outer pane to exhaust any moisture that  
got into the air-space.  In century-old homes, where air-leaky sliding  
sash and trim were common-place, the ventilation holes were huge (ie 4 x  
1.5-2" dia holes)   In Pella [spit!] windows in the 70's & 80's of the  
previous millenium, where the window units are kinda tight, the vent holes  
would be two 3/8" dia holes.

In old sealed insulating glass units, the vent hole would be one 1/8" dia  
hole.

The size of the vent holes that you'd need would, I imagine, fall  
somewhere between Pella's [spit!] and the
1/8" hole in the old IGUs.  That would be the quick/dirty solution to your  
problem.

The better solution would be those mentioned by Mike and Topher ...  
interior storms with very good air seal and lowering interior humidity,  
either by exhausting it at the source and/or dehumidification.

Unfortunately for me, those Pellas [spit!] that I installed in my home  
have proven to be very longevous
(no edge seals to fail, aluminum cladding on frames and sash) so they're  
still being used. I dealt with the lousy air seal of the removable inner  
pane by making interior storms which snap into the space which the  
(inteior) insect screens vacate when cold weather comes.

I went to the local H4H ReStore and got a bunch of 4 mm glass that was  
used in 1950s-era sash-less sliding windows and inserted the glass into  
mini-frames made out of 0.5 " x 1" pine, with Shoji/Greene & Greene-style  
muntins to restrain the long flimsy perimeter pieces. The interior storm  
creates a 13/16" air-space.
The interior storm sash is made smaller than the actual opening to allow  
for a screen spline "gasket" to be compressed into the gap to provide the  
air seal. The screen spline is reusable year after year but you could use  
your peelable caulk if you can't be bothered futzing with the screen  
spline.

As a belt & suspenders strategy, I also insert a piece of silica  
gel-filled spacer bar (salvaged from dismantling patio door IGU) at the  
bottom of the air-space and include a brake-formed sheet metal  
condensation gutter (to match the profile of the bottom sash rail (set in  
place before the storm is put in).


--
=== * ===
Rob Tom					AOD257
Kanata, Ontario, Canada

< A r c h i L o g i c  at  Y a h o o  dot  c a  >
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