[Greenbuilding] Double stud vs foam outsulation/single stud ( was re: (not )Outgassing of Sheathing & Insulation fasteners

[RT]

On Wed, 28 Nov 2012 13:13:24 -0500, John Straube <jfstraube at uwaterloo.ca>  
wrote:

> Double stud walls (DSW) have been used since the late 70s to reach super  
> insulation.  Problems with condensation accumulation at the outer layers  
> have been reported since then.

No doubt, a result of improper detailing and execution but I'd venture  
that the same sloppiness in a foam-outsulated 2x6 wall would result in  
worse moisture problems due to the relative vapour-impermeance of the  
foamed plastic.

I have cut open properly detailed/executed DSW during  
renovations/additions and found them to be in perfect condition.


> Double stud walls also continue to have some rather significant thermal  
> bridges at floors relative to a complete blanket of insulation.

Again, an issue with improper detailing.

There's no reason the joists can't be stopped at a ribbon joist located  
over the bearing wall which logically would be the innermost wall. An  
unbroken-by-framing layer of insulation (typically a minimum > R-20 for a  
minimum-thickness DSW) would be provided between the structural joist  
header and the curtain wall ribbon joist.

In Eli's case where he's using a frame bearing wall AND 2x furring anyway  
(ie the same volume or more of lumber that would be used to make a DSW)  
why bother with the added cost/futzing needed to deal with a 6-8" layer of  
foamed plastic ?



-- 
=== * ===
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  >
(manually winnow the chaff from my edress if you hit "reply")