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What goes in to a home insulation decision

Marc Lefkowitz  |  12/07/11 @ 4:00pm  |  Posted in Home efficiency

This is part two in a series following one man's journey to weatherize his family's wood frame house built in 1920. Part one, he discovered how drafty walls sans insulation and with big gaps in the frame explained huge heating bills and a family shivering under blankets. Determined to seal it tight(er), we saw the results of the home energy audit and now join him as insulation contractors and financiers are engaged.

By now, we've all heard the reasons for insulating our homes-buildings are the main culprit (40%) in our consumptive energy use. Insulation is a place where we can intervene; to me, it may be the single most empowering "local" action in my quest to lighten my ecological footprint. But, looking for what insulation works best with an existing home, the process is long and fraught with trade offs.

Lucky for you, dear reader, I've spent the better part of a fortnight parsing through the sidewall, attic and basement insulation options – standard ones which don't require tearing out walls or radical redesigns. Let me just say, I can understand why only 4% follow through on their home energy audits – you have to really want it like I do and have the time to research the best option for you – both are in scarce supply at times for those who don't blog about this or live and breath it.

I determined that my lens for deciding on insulation will be ordered this way:

  1. Health and safety (does it release noxious fumes into my home? Is it even more toxic in a fire?)
  2. Performance (how well does it slow the transfer of air, measured in R-value; how well does it literally hold up/longevity)
  3. Lifecycle – is its production, application and end of life sustainable (does it do less harm)?
  4. Cost effectiveness (what is the payback in years?)

I'm discovering that all insulations-based on my criteria-have trade offs. Looking at compositional analysis and reviews from construction professionals, not one of them is without its pros and cons.

I'll cut to the chase. My current favorite is a cementitious foam product that can be pumped in to sidewalls. It gets high marks for indoor air quality, longevity and moisture resistance. This last one is a biggie, since blow-in cellulose scores the highest in its sustainable lifecycle (foam is not nearly as 'green' as cellulose which is 80% recycled newsprint), and cellulose is not far behind in health and safety.

Cementitious foam products, like AirCrete, are 'open cell' which are spongy and lightweight and "allows some vapor to pass through, making it a good choice in hot, humid climates, and under roof sheathing, such as in conditioned attics, where water vapor caught between insulation and sheathing could promote wood rot," according to Eco Home Magazine. (The article does a nice job laying out the pros and cons of foam insulation).

The more dense, synthetic 'closed cell' foams promise double the R value of the open cell-both are not very green; But with most applications of synthetic closed cell, serious questions are floating around about its health and safety. This generation of synthetic foams still contain formaldehyde, a known carcinogen. It is difficult to ascertain exactly how much from the companies who produce and sell the product line of Tripolymer foam, although it has been reported they have less than the 1970s urea formaldehyde.

On top of that, their "blowing agent" produces CFCs, an ozone killer. A recent Environmental Building News article caused a stir when it steered consumers away from synthetic foams because it has 100 times the global warming potential of the air-pumped foam.

There's no one size fits all solution. With a small child at home, I choose to give more weight to indoor air quality and safety than someone else might. AirCrete is composed of silica and lime and something called magnesium oxide which its industry reps say actually sequesters carbon dioxide. It supposedly uses no fire or pest retardants, so it doesn't off gas VOCs.

Cellulose, which is probably running a close second at this writing, is treated with borac acid, which has been known to cause irritations of the respiratory system as it dusts into a living space when the paper breaks down (here's the Material Safety Data Sheet on cellulose insulation). The insulation contractors I've been speaking to all assure me that with proper air sealing from the interior of our house-caulking around the floorboards, etc.-will keep the dust out.

I'm not ruling out cellulose, yet – it's the cheapest, and undeniably has a lower carbon footprint in its lifecycle compared to foam. It seems to be the popular choice, but questions are out there about its longevity.

I ask Environmental Health Watch green building consultant and contractor Matt Burgess to compare foam and cellulose for my wood frame house. I'm concerned that my house will retain moisture and make cellulose insulation wet.

"It depends what is on the exterior-what is behind the siding," Burgess answers. "In some cases, there is wood siding nailed directly to the studs, which is most problematic. If there is black or brown paper behind the wood, that is a good thing, and either product would probably be fine.

In either case, regardless of the product, you want to keep bulk moisture out, have back up drainage in place to deal with wicking, and do what you can to ensure a good install (i.e., infrared camera inspection before, during, and after)."

A lot is riding on whether back in 1920 the builder had the wherewithal to nail up paper behind the siding. Otherwise, Burgess adds, "If there is an imperfect vapor barrier under the siding, and if moisture is likely to be wicking into the wood siding, and water gets behind the siding, then I don't want cellulose getting and staying wet."

I'm also wrestling with the upside of synthetic foam. Reportedly, it has double the R-value at 6.4 pounds per inch-compared to AirCrete and cellulose's 3.5. Would I diminish the impact of this one chance to fill my walls with insulation and maximize my carbon-reduction impact?

Yes, but for better or worse, I'm committed to health and safety as my first cut. Small children are especially susceptible to volatile organic compounds, so I have to lay down my green performance geek hat. Of course, it's not hard to find evidence to support one's decision once you have. Polyurethane foams with formaldehyde resins are banned in Canada, California, Vermont and are now under investigation by the EPA for their health risks.

The mainstreaming of green building is bringing changes to the insulation industry. Some new products, like Spray polyurethane foam (SPF) foam are entering the market, and promising a small percentage of soy content along with synthetics formulated without formaldehyde. Some of these SPF products were recently certified by Greenguard Environmental Institute, a third-party rating organization focused on indoor air quality.

I'm also reading that the way foam is applied is vital to its longevity. The installer must compensate for air temperature and moisture or you could end up with a goopy mess or worse-not enough to fill the cavity. This post on Green Building Advisor talks about shrinkage-no, not the George Constanza kind. The vaunted R value of foam could be squandered without a good install. Reportedly, walls have been opened up to find big gaps between the foam and all six sides of the wall cavity. Of course, the foam companies all shoot back that this is fear mongering, but it does make you appreciate how 'idiot proof' the installation of cellulose would be.

One final word on R value-our uninsulated wall is currently R-3-cellulose and open cell foam would raise it to R-11 (which is up to code for new construction here) and closed-cell foam would get it to R-18 (which is EnergyStar rated for our region). One of the questions that needs answering is, how much are you willing to pay for the additional seven points in R-value (some of that depends on how confident I am that natural gas prices will continue to rise)?

Obviously insulation has come a long way since your dad brought the pink stuff home in the back of the station wagon and with armfuls of rolls pressed against his white t-shirt headed for the attic. When did insulation, like everything, get so complicated?

* * * *

One more word on cost. I'm starting to look at quotes on whole house insulation and air sealing. It appears that the cellulose folks are slightly cheaper than the synthetic foam company. Although that is premised on the foam guy's claim that air sealing is redundant because, he says, foam fills all gaps, including the interior space. I double check this claim with Burgess, who replies:

"The foam would better seal the cavities, but the air leakage you are speaking of is not necessarily coming from within the cavities. You would add some caulking to either approach to do better. It is very hard to put a true value on the air sealing job, and the difference between the two options until you know how much air leakage reduction you got out of it. The foam would do well around outlets since it would expand against it in the cavity."

Looking at sidewall insulation alone, cellulose is about 1/3 the cost, but it is also half as effective in R value. I'm still waiting for a quote for AirCrete, but open cell foam reportedly costs somewhere between cellulose and synthetic foam. Next up: the details of the payback period based on the Department of Energy's payback calculator – the formula factors in the cost of the insulation, what you pay in energy per unit and the efficiency of the insulation.

(update: I spoke to an AirCrete installer who says, depending on the wall, the cost range is $2-3/sq ft.; cellulose blow in, by comparison, is around $1-$1.30 sq. ft)

(update 2: I just did the math using the DOE payback calculator and it looks like the payback period for our situation before any rebates for cellulose blow in would be 3 years and for AirCrete the payback would be more like 6.25 years)

Also, a word about the Dominion/GoodCents rebate. I called all 31 companies on the approved contractor list, and only one, USA Insulation, offers foam pumped into a close walled, and it's Tripolymer. I did receive a quote from them, but I'm now considering foregoing the rebate on the sidewall insulation if I can determine if AirCrete measures up.

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