The insulation riddle is back!

It feels like the project and my life have been taken over by insulation issues—whether they have to do with physical prep work or keeping me mentally on my toes, thinking about how to insulate.

Interestingly enough, some things that seemed resolved suddenly make a surprise re-appearance.

I learned about the “point of diminishing returns” for spray polyurethane foam (SPF) in late 2009 but couldn’t quite wrap my head around it. In early 2010, a comment on the blog post pointed me to an Icynene publication that explained the phenomenon.

It turns out that it is not so much explaining as it is a marketing gimmick. One of the blog readers, Tom Donalek, submitted two interesting comments on the insulation riddle post, in which he mentions a discussion at

Tom points me to the comment section of that discussion that gets into the subject of diminishing returns:

… down in the comments, there’s some talk about this “mind bending” stuff about getting the “first 89% of the insulation value with 2 inches of foam.”  It appears to be some good old advertising statistics.  These numbers like “80% with one inch, and 89% with two inches” are in comparison to what, exactly?  One of the commenter points out that it’s in comparison to a wall with an R value of 1.

At the end of the first paragraph on page 2, they [Icynene] say, “Stated another way doubling the insulation thickness (R-value) and cost; only provides a modest 2% increase in heat flow reduction.  Based on this observation, it is very difficult to justify the additional cost of adding insulation beyond 6″ in thickness.”

I think that the above sentences were the whole goal of the exercise, and they had to do some gymnastics in order to create a starting point, no matter how odd, that would get them to that goal.  The cost of spray foam insulation is its main competitive disadvantage, and this exercise is intended to deflect from that disadvantage.  This comes at the potential cost of under-insulating a building, resulting in increased heating and cooling costs for years to come, with the associated carbon release.  As with the discussion I linked to […] it appears that Icynene may be quite willing to make some “extraordinary” arguments in order to benefit their product/business.

This isn’t quantum physics – it’s good old, straightforward low-energy physics.  Yes, convective heat loss (air leaks) is very important, and radiant heat loss also plays a role.  But most of a house’s heat loss is conductive.  When you plug through the simple math, R values are R values – there’s no mental gymnastics required.  R-40 means half the conductive heat loss as R-20, and R-80 would mean half as much again.  No “wrapping your head around it” required.”

And I guess no real point of diminishing returns either… You can read the unedited version of Tom’s comments at the “Insulation riddle resolved” post.

This type of confusing data and greenwash is a reoccurring problem in the green age and it is not always easy to separate the wheat from the chaff.

Having narrowly avoided this trap, I should take another look at our insulation strategy to make sure that we still meet our energy goals.

About Marcus de la fleur

Marcus is a Registered Landscape Architect with a horticultural degree from the School of Horticulture at the Royal Botanic Gardens, Kew, and a Masters in Landscape Architecture from the University of Sheffield, UK. He developed a landscape based sustainable pilot project at 168 Elm Ave. in 2002, and has expanded his skill set to building science. Starting in 2009, Marcus applied the newly acquired expertise to the deep energy retrofit of his 100+ year old home in Chicago.

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