The advantage of a slow moving project is that you don’t rush into decisions you may regret later on. This is certainly true for the decisions on insulation, which are rather significant.

I have researched and thought about the insulation for one and a half years and received numerous helpful comments and references. What once was a very exotic subject has become very familiar.
Insulation or outsulation?

We started with the dream of insulating the masonry shell from the outside (outsulation), leave the brick work exposed on the inside and use it as thermal mass. Whenever I advocated that idea, I was promptly discourage from doing so.

That said, it appears to be the favored option of some green industry professionals. The principle reasoning is that it protects the masonry structure from freeze-thaw cycles, which can be detrimental if the brick or stone work is saturated.

I bet there are existing masonry structures out there that lend themselves to outsulation, that have enough dimensional room around the building to accommodate the extra layers and have fire code requirements that would allow it.

We are not so lucky with the west side of our building partially located right along the property line and ornate architectural features on the front elevation that I will not dare to cover up.

So – insulation it is.

Recycling relieve?

My research on insulation materials pointed me pretty early on to spray polyurethane foam (SPF), as it performs a number of functions. It provides the air, vapor and thermal control layer.

The two things I could not shake, though, were the issues that a) SPF is a petroleum based product, and b) the question of end-of-life use—or, what happens to the foam once it gets ripped out?

As it turns out, spray foam scraps don’t have to go into a landfill, but can be turned back into resins and reused in another SPF application. I hope that this is not one of those “too good to be true” stories.

With regard to the petroleum based content, the industry is now also marketing foam products with renewable resource content derived from soy or castor beans. But even with the addition of renewable resources, SPF remains largely a petroleum based product. The other remaining question is how sustainable soy farming is.

How about a high recycled content material?

An idea emerged while we were installing the perimeter wall framing. Rather than spraying the entire six to seven inch interior wall cross section with SPF, we could only use the foam in the three inch gap between the masonry wall and the framing. Then we could fill the three and a half inches of framing with a batt system.

There are several products that have a high recycled content. The first one I investigated was a cotton batt product with 90% recycled content. The recycled cotton batts have good thermal resistance and sound absorbing properties, plus they are more economical than SPF.

What worried me a little is that cotton is good at absorbing moisture (think of the good old sweatshirt). Moisture content in the batts may reduce their thermal resistance and begs the question about mold growth.

To reduce the risk of mold the batts are treated with a borate solution (boric acid). I am not sure how I feel about introducing yet another chemical into our indoor environment.

At one point I listened to a GreenBuildingAdvisor.com podcast in which rock wool was mentioned as an insulation material. The one thing that really stuck with me is that rock wool – made out of rocks and slag – won’t burn. That did sound awfully attractive and I researched this some more.

Rock wool insulation is manufactured in batts of all sort of sizes, has good thermal resistance and is easy to handle and cut. It is not treated with boric acid, is manufactured with a high recycled content and even more economical then the cotton batts. Bingo!

Updating our insulation plans

We need an effective air seal to meet our energy goals. SPF is the most effective product to achieve this objective. Plus, SPF also acts as the vapor and thermal control layer in the wall assembly. We pay more, but we also get more.

It makes sense to stick with our original plan and use a one inch layer of closed cell foam on the masonry wall. That closed cell foam must have a perm rate of greater than one.

Rather than filling the rest of the wall cavity with open cell foam, we deviate from our original plan and plan on only adding two inches, which gets us to the back of the wall framing.

To reduce the environmental impact and drive cost down, we fill the wall cavity space in the framed section with rock wool batts.

This insulation assembly should give us an R-value of 26 to 28.

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 GreenBuildingAdvisor.com.

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.