[Greenbuilding] insulating around windows... best practice

RT archilogic at yahoo.ca
Thu Sep 5 18:52:32 CDT 2013


On Thu, 05 Sep 2013 03:00:39 -0400, Reuben Deumling <9watts at gmail.com>  
wrote:

> I like backer rod. My method has evolved into stuffing the appropriate
> diameter backer rod from the outside and from the inside around the
> perimeter of the window.


I tried canned expanding foam once, way back in the 70's or 80's of the  
previous millennium when the manufacturers started to boast that their  
product didn't use ozone layer-thinning CFCs as a propellant any more.

I didn't like the stoopit stuff because it had a tendency to bridge small  
gaps before completely filling the cavity, made friggin' mess, was a PITA  
having to trim off the protruding crud, made a friggin' mess and no doubt  
a bunch of other irritants that I've long since forgotten about.

However, one good thing came out of the experience.

To address the issue of foam bridging the gap before filling the cavity I  
simply made the framing for the rough opening larger than the sizes that  
window manufacturers recommended ... say up to 2" larger in width and 1.5"  
larger in height than the actual frame size (rounding off the dimension to  
a whole number)... but cut the opening in the sheathing very close to the  
actual window size.

Then when it came to insulating the shim allowance, it dawned on us that  
since the gap was so large and accessible, there was no need to use that  
stoopit foam-in-a-can that *everybody* hated.

There was always plenty of EPS scraps around and it was a simple matter to  
measure the gap that needed to be filled and rip strips of the EPS scraps  
to fit, oversizing the strips so that they needed to be compressed in  
order to be shoe-horned into the gap, using 12" drywall knives as the  
shoehorns and insertion tools made from scraps or OSB or plywood to  
efficiently push the EPS in without damaging the EPS.

But as BCJohn mentioned, insulating the framing gap was only part of the  
story. Ensuring continuity of the air barrier by first wrapping a strip of  
12" wide black poly around the outside of the window frame (and providing  
an extra 8" of length & double folds at each corner to allow for effective  
joining to the inside & outside air barrier membranes) was also done.

=== * ===
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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