Basement Insulation Options: Rockwool Rocks!

Last week we got insulation. Not only were we thrilled about not having cold feet anymore (the empty ceiling in the basement leads to a chilly floor upstairs), but this also was a huge milestone because it meant that we'd passed some big inspections. Since insulation (and then drywall) covers up the plumbing, electrical, and framing work, the fire inspector had to come and approve everything done so far, first.

The boys celebrate insulation day

Choosing a green insulation was a decision that flummoxed us. While soil is nature's built-in insulator for basements, and the cinder block that our house is made of also contributes R-value (measure of thermal resistance), we wanted additional insulation  to make our space cozy. Choosing insulation proved to be a challenging decision, as there are differing opinions on what  is greenest that works for a subgrade basement. Our research led us to these finalists:

Fiberglass- This "pink stuff" is all I knew of when I started. This is bad stuff to breathe in, but the continuous roll version, for use in walls, comes lined with paper that makes it cleaner. Plus, I learned that there are some greener options that are very low VOC and are partially made from recycled materials. Owens Corning EcoTouch is formaldehyde free, 58% post-consumer recycled content, comes in many great R-values, and is very affordable. I felt good about going this route as long as we used this brand. Alas, at the DC Green Festival, I heard the owner of Amicus Green Building Center speak and he pointed out that while some fiberglass may be greener, it is not green. It's that whole idea that not bad and good are two different things. It was a wake up call to me that in terms of cubic inch, insulation will be the highest volume of a single product that we have in our basement. I decided that this needed to be a splurge area in not only for indoor air quality but also in terms of production. Fiberglass was out.

Foam- Foam insulation can be sprayed in or installed in sheets. I was leery of these from the start as they are made from polyurethane and thus petrochemicals. Since we live a minimal-plastic/synthetics lifestyle, this just was contrary to all that we've already worked for in our house. Production and disposal are red flags; in the case of a fire, foam is toxic if burned. In terms of indoor air quality, foam is a mixed bag. Open cell vs. closed cell foam still confuses me a bit, but here is what I think I've got right from asking loads of questions to contractors and the Amicus folks. Open cell foam is better in terms of off-gassing because it only off-gasses ammonia. However, it takes longer to off-gas than closed-cell foam does, and it is not a popular choice for subgrade spaces. Closed-cell foam has an initial burst of off-gassing, but then it is done. It also has a better r-value per square inch than open-cell. In our brief foray into considering foam, we looked at GreenGuard certified Owen Cornings Foamular (rigid closed-cell foam boards) as well as spray foam. Ultimately, I just couldn't get on board with this, despite talking about it with vendors at the DC Green Festival and talking to a green contractor who closed cell spray foam in his own basement.

Wool- Yes, the stuff from sheep. We are a bit wool-obsessed at our house right now: wool rugs, wool dryer walls, wool sweaters, wool pants, wool diaper covers. So, why not wool insulation? Just like how wool clothing keeps you cool in the summer and warm in the winter, wool insulation does the same for a house. It can absorb a huge amount of moisture (though hopefully a house isn't very moist) without any thermal change. It is fire-safe, like all insulation must be, and it is inhospitable to vermin. This is a very attractive option, but we didn't feel like we knew enough about it for a sub-grade space and, even with splurging on insulation, we wanted a cheaper option. I would consider it for our attic, someday, though! Learn more about it, here.

Rockwool- This innovative insulation is made from volcanic basalt rock, abundant in the earth, and slag, a byproduct of the steel and copper industry. The materials are spun into fibers that resemble wool and made into batts or boards. (The boards are brand new to the US.) It is breathable (yay for good air quality), but cannot absorb moisture. If it gets wet, the water just drips right off. Mold cannot grow on rockwool. Rockwool does not off-gas and they are non-combustible, in the case of fire. Its R-value is competitive with fiberglass, but it shines above it because of the eco-friendliness of production. It also provides better sound-proofing than synthetic insulations. While it is more expensive than fiberglass, it is not prohibitively expensive. This was our winning material! Check it out in our house:

We were expecting Roxul Comfort Batt, but our contractor's supplier sent Roxul Acoustical Fire Batt (AFB)  instead. I only noticed the alternative product when posting the picture below to this blog entry and then freaked out because the insulation had already been encased by drywall, which had already been mudded and sanded. Needless to say, we had a very stressful 16  hours before we got in touch with the supplier, the inspector, and  Roxul's customer service. I learned that Comfort Batt is more commonly used for residential projects these days, as it is a newer product better sized for the way US houses are framed. AFB is the same material, it just needs to be cut more to fit interior framing widths. Comfort Batt placed on exterior walls typically gets a vapor barrier on the interior wall, but the AFB does not include that in their instructions. Because the Northern Virginia climate does not get frigidly cold, we are comfortable with having no vapor barrier.  Our contractor learned that the inspectors had also been held up on this issue and talked with Roxul before issuing approval. Ah, the joys of using products that aren't rare, but aren't common either.

 

The picture that struck fear in our hearts.

AFB has an R-value of 4.1 per inch of thickness. That is a well-insulated basement when you add up all the components, which is a good thing since putting in ample ductwork for HVAC wasn't in the budget.