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

[John Straube]

Embodied energy goes by whatever units make sense.  But for a material it is common to do it in energy units per mass units, Btu/b or J/kg, or kWh/kg, etc.
You definitely need to adjust for mass.  If you use a cubic foot of concrete it weighs 140 pounds and EPS weighs only 1.5 to 4 or so depending on the grade.

The balance question is of course key.  I doubt there is an answer. I would like to aim for lowest embodied energy while meeting the requirements of durability affordability availability constructability comfort, health, safety, and serviceability.  I would be suspicious of investing more than say 10 or 20 years of energy into insulation, even though I know the building will usually last 30 to 100 years.  But of course, the embodied energy of a countertop, or a toilet will never “payback” so it has an infinitely high impact.  

On Dec 10, 2014, at 7:16 PM, Ross Elliott <relliott at homesol.ca> wrote:

> If embodied energy goes by weight, perhaps a hundred pounds of EPS goes a
> long way? Its GWP is lower than other foams since it uses air as the blowing
> agent.
> 
> On the subject of polyiso foamboard, it tends to perform worse the colder it
> gets.
> http://www.greenbuildingadvisor.com/blogs/dept/musings/cold-climates-r-5-foa
> m-beats-r-6 
> 
> Where's the right balance between energy embodied in a product vs. how much
> energy it saves over its lifespan? My own house has lots of foam in it, they
> tell me it's made from soybeans and pop bottles so it must be good.