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

[John Salmen]

I like option 1 if you are expecting the block to dry to the exterior - but not the treated 2x against cement block and metal Z not great thermal breaks – I’ve been using recycled hdpe lumber as a substitute for treated location requirements – high cost depending on what is available locally but I use cosmetic rejects from a local decking manuf. at a reasonable cost. Great sill material and generally an engineered material so can be certified for load bearing or fastener holding if need be. 

 

I like the subtraction concept – hopefully see more of that being done in future reno work. I would guess new trusses as being the least material / lowest cost / highest benefit / integrity. Moisture conditions in the attic would be a concern – from experience I can say that venting with wet winter air is not effective. Cellulose fill is moisture tolerant but that is not the same as moisture cycling.

 

From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Alan Abrams
Sent: December-12-14 7:37 AM
To: Green Building
Subject: Re: [Greenbuilding] embodied energy was Polyiso strength on roof (ErgoDesk)

 

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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