[Greenbuilding] embodied energy was Polyiso strength on roof (ErgoDesk)

Alan Abrams alan at abramsdesignbuild.com
Fri Dec 12 09:36:41 CST 2014


to me, the question is immediate. A current project is the gut rehab of a
modest '40's house, with walls made of stuccoed concrete block. It is
compelling to insulate the walls on the exterior, to provide as much
interior area as possible, and to harness the thermal mass by optimizing
solar gain and shading. But the climate is swampy in summer, and the house
is situated near an old water course. So the potential to create a mold
incubator is significant--particularly if winters become warmer and wetter.

Current thinking is to fasten treated 2x's directly to the masonry, with 1
1/2" thick Roxul Comfort Board installed between members. The 2x's go on
first to assure a good mechanical connection to the masonry. Then cover
that with a continuous layer of more RCB, a good breathable WRB, furring,
and back vented siding.

another option would be mastic adhered EPS, and synthetic stucco. Or EPS,
with furring secured through the foam into the masonry. This option strikes
me as very risky, drilling through the furring, foam, and CMU, to provide
pilot holes for Tapcons or similar fasteners. The length of the fastener
becomes a serious limitation, too--not only their availability, but their
cost. And for any variant using EPS, more reliance on mechanical
dehumidification.

The roof is another opportunity for muddling. The plan is to remove the
entire second story, which had grown haphazardly over the years. Many
advantages here--a single occupant already with one bionic knee--less
volume to temper, lower real estate taxes. (making this project a
"subtraction" instead of a more typical addition...)

A quick and easy solution would be a set of SIPS, set on a low pitch.
Alternately, simple engineered roof trusses, with loose fill something or
other. The one is simple and direct, easy to create tuned overhangs. The
other, conventional, breathable. Cost will probably be the determining
factor.


AA



On Fri, Dec 12, 2014 at 9:09 AM, Alan Abrams <alan at abramsdesignbuild.com>
wrote:
>
> not to muddy these already murky waters, but there are at least two other
> factors that come into play.
>
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