[Greenbuilding] first certified Passive House in Canada

[Frank Tettemer]

>  Ross Elliott wrote:

>  Concerning difficulty in air sealing to this level, I saw some great 
examples of using the structural sheathing layer as the air barrier > 
when I was at the PH conference in Portland, OR this year, sure seems to 
be a better way than poly and tape and acoustic sealant > for getting 3X 
tighter than R-2000. Freaks out some building officials though.

Firstly, congrats to Ross for the newly certified.  It's a fine thing.

John and Ross, this thread has been a fine untangling of mythical 
information, that has puzzled a hammer-head-builder like me for years 
now.  I'm feeling pretty good now about some of my post-construction 
worries.
Almost.

I've been building energy efficient homes, using one out of the 
following three wall systems for the past decade, depending upon the 
customer's needs.  It's either been plastered straw bale, or, 
double-frame 2x4 with cellulose blown in, or 2x4 frame with roxul and 
3"+ foil-backed ISO on the exterior.  My post-construction observations 
have made me quite confident of the construction details for the first 
two systems, but gently un-nerved by the latter system.

Concerning that system:  I'm guessing, Ross, that your comment above 
relates to such a system.  Could you elaborate a bit more about the 
details of construction for this?
Mostly 'cause it freaks me out as well as the chief building officials!
I've built with 2x4 frame, with polyisocyanurate panels added to the 
exterior, with seams taped with aluminum 3" tape, since the ISO became 
commercially available.  So far, I haven't witnessed problems, but then 
again, I've not had to take any of the walls apart, to see what's going 
on inside them.

My concern is, of course, the double vapour barrier: One on the inside 
("Super Six" plastic vapour barrier, all seams lapped and sealed with 
acoustiseal), and the second one, out past the inner insulation of R-14 
Roxul batts, (namely the foil-backed ISO).
I've rationalized this set up by the thinking that I've placed the 
middle vapour barrier about 1/3 of the way through the wall's 
insulation, (R-14 inward, and R-21 or R-29 outward).  And for this very 
reason, (as well as saving lumber), I've framed with 2x4 instead of 2x6, 
since a 2x6 wall would give me R-21 on the inside of the ISO sheathing. 
And to balance the equation, with a 2x6 frame, I'd need to have R-60 on 
the outside of the frame wall, which is more than most customers would 
care to pay for.
In these wall sytems, I don't use plywood sheathing at all. I brace all 
frames, while lying on the deck, with metal T-shaped wind bracing, let 
into the wooden frames, to deal with racking.  Seems to work fine.  And 
with very long screws, fastening horizontal 1x4 strapping at 16" o.c., on 
the outside of the ISO, screwed into the vertical studs, I can then 
fasten vertical wooden siding, with a 3/4" air space, over the ISO.

This "seems" to work fine, but is unsettling, 'cause it breaks the 
"rule" of having only one vapour barrier, and makes me tend to worry 
about mold growth inside of the Roxul, next to the ISO foil barrier.
What do you all think about this seeming contradiction to the building 
code?  Does it work, as it appears to?  And if it does, why does it?

Cheers,
Frank

Frank Tettemer
Living Sol ~ Building and Design
www.livingsol.com
613 756 3884