[Greenbuilding] Best bang for the buck in wall insulation

Wed Mar 26 10:42:01 CDT 2014

here's where I'm heading--envelope design in my mixed humid clime is going
to be based on:

two way permeability
configuration that facilitates a continuous air barrier--therefore:
a config that combines the air barrier with rain screen
enough exo insulation to keep the sheathing above dewpoint in cold weather,
and to reduce thermal bridging
simplicity--fewest number of layers
elements outside the rainscreen to be highly resilient

(I should also confess that I have succumbed to FAS--Foam Avoidance
Syndrome)

so with that rationale, the ideal assembly would be, from the exterior in:

*cladding on treated or carefully primed furring, secured with SS fasteners
(for low thermal conductivity as well as corrosion resistance)
*a permeable WRB like Solitex Mento
*3" or so roxul comfort board
*Zip sheathing, taped, as air barrier and secondary WRB.  Flange type
windows and doors taped to the Zip board
*OVE stud wall
*a void, width determined by specific space heat demand analysis
*an inner frame wall
*the entire framing cavity filled with DP cellulose
*drywall, painted with permeable coatings

Having the air barrier on the face of the sheathing avoids the difficulty
of maneuvering an interstitial air barrier around floor systems, windows
and doors, jogs, overhangs, and other obstacles. it also reduces the
possibility of water vapor intrusion in summer, and would reduce the
intensity of convection in the framing cavities, where there may be
imperfections in the dense pack.

I am not convinced that this assembly would need a special interior vapor
barrier. I'd use airtight electrical boxes and make a reasonable effort to
seal other penetrations in the drywall, but would rather not add any layers
that would potentially impede drying to the interior

=AA

Alan Abrams

*certified professional building designer, AIBD certified passive house
consultant, PHIUS*
*certified passive house builder, PHIUS*
Abrams Design Build LLC
*sustainable design for intentional living*
cell     202-437-8583
alan at abramsdesignbuild.com
www.abramsdesignbuild.com

On Wed, Mar 26, 2014 at 11:00 AM, Joe Killian <kaa-ajk at sonic.net> wrote:

>    Yes, Roxul looks  like a great choice.  Canadian Home Depot stores
> list their residential product at comparable prices to fiberglass.
>   I was able to find the commercial Roxul products from a distributor here
> in Sacramento (I'm in Nevada), and they were happy to accept a large order
> (roughly a full 53' container load) for Roxul's residential product.
> However, the factory told them they would not sell the residential product
> in the U.S.
>   Joe
>
>
> On 3/25/2014 12:56 PM, Jason Holstine wrote:
>
>
> The Roxul Comfortboard has been gaining steam and reputation as a
> replacement for the plastechhh foam boards. Much lower GHG potential and
> toxicity, doesn't burn (made of recycled steel and volcanic rock), deals
> with vapor and water nicely, tight, quiet, and Roxul is picking up
> documentation on hanging it.  Only downside is availability in your area
> may still be dicey.
>
>
>
>
> On 3/25/14 10:53 AM, "Lynelle A. Hamilton" <lynelle at kos.net> wrote:
>
> > For true!  I'm planning on some sort of sheathing as you describe. I
> > used 2" of closed cell spray foam last time over outer side of 14"
> > insulated Dursiol block.  I love the house and the airtightness of it
> > (assuming airtightness is a word), but it was a pricey option.
> >
> > Lynelle
> > On 3/25/2014 10:43 AM, Clarke Olsen wrote:
> >> Don't forget that uninterrupted insulation, like foam spanning across
> studs,
> >> or cellulose in the center of a double wall,
> >> is worth more then the same stuff stuffed between studs.
> >> Clarke Olsen
> >> clarkeolsendesign.com
> >> 373 route 203
> >> Spencertown, NY 12165
> >> USA
> >> 518-392-4640
> >> colsen at taconic.net
> >>
> >>
> >>
> >>
> >> On Mar 25, 2014, at 9:28 AM, "Lynelle A. Hamilton" <lynelle at kos.net>
> wrote:
> >>
> >>> Hi Listers,
> >>>
> >>> I am looking to tap the collective expertise of the group for house
> #3.  I
> >>> am aiming for R-50 or so in the walls, but would love opinions on the
> >>> greenest and most cost effective method to attain same.
> >>>
> >>> Any thoughts?
> >>>
> >>> Lynelle
> >>>
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