leangreen.org recycled renovation on a low-budget ration

Here in California, one decision has been made for us: our insulation’s minimum R-value. Our Title 24 Report calculates our expected annual energy use based on the house’s orientation, climate zone, and design. Our report assumes we’ll have an 84% efficient natural gas boiler, for instance. The report then prescribes the following insulation requirements: roof at R38, exterior walls at R21. We’re happy to have this decision made based on some calculation rather than an endless row of tabs on my browser.

THE ROOF
On the rear addition, our roof is simply constructed of 2×12 joists spaced at 24 inches and we need to leave a 2 inch air gap at the top for venting to reduce condensation. To achieve R38 within a 10 inch depth, we have two options: blown-in cellulose or high density fiberglass. Because roofs can leak, we’re wary that cellulose will collapse and mold over time. Although it has low embodied energy and high recycled content (85% post-consumer newspaper), if it doesn’t perform well over the long-term, it just isn’t worth it. For fiberglass, we like the Knauf Ecobatt: manufactured in Northern California, made from 30% post-consumer recycled glass with a petroleum-free and formaldehyde-free binder and without bleaching agents. Spinning glass takes a lot of energy, but the high density batts should survive a minor leak or at least be easily patched. We’ll buy the paper-faced type so we can easily staple it to the joists. It runs at 80 cents per square foot, not a big stretch from 66 cents/sf of cellulose. And we can handle it ourselves.

EXTERIOR WALLS
For R21 insulation of our exterior walls, we fear the same issue with cellulose and water. We also have many penetrations and obstacles in the walls, leading us to consider two more options: water-based spray foam, such as Icynene, or the recycled denim batts, such as UltraTouch cotton. With 1400 square feet of perimeter walls, price becomes a big factor too. One estimate for Icynene installation (not D-I-Y) was at $2 per square foot! We’ve read about its air-sealing qualities and we’d love to fill in every little crack and air leak, as there are many. But we also have the time, patience and commitment to fill cracks and seal leaks with foam (we already bought a case) and caulk (another case). Water and Icynene also present a disaster potential: it absorbs water and can mold. Unlike a batt or loose-fill insulation, which you could remove or vaccuum away, the foam needs to be sandblasted to get it out (this guy’s account of Icynene mushrooms in his bathroom walls really made us think). Like a Mercedes, you pay top-dollar upfront and then top-dollar to fix it when something goes wrong. Although we’ve worked hard to prevent leaks in the first place, we know there’s no guarantee.

FIBERGLASS VS. COTTON
Currently, we have JohnsManville R19 fiberglass insulation in our garage walls (for interim during-construction climate control). Where its a straightforward run between studs, no interrupting wires or pipes, it has held up well. We can still hear our neighbor open her front gate and unlock her car door, so its sound insulating qualities seem low. Where we’ve had to route the batts around obstacles or fill an odd-sized cavity, the fiberglass is smooshed, disheveled and failing to rebound. Although fiberglass cuts easily, especially with pre-perforated batts, I’m doubting our ability to insulate really well around obstacles. For comparison, we bought a few bales of the UltraTouch Cotton recycled denim insulation this weekend. At 90 cents per square foot, it’s double the cost of fiberglass. It was difficult to cut with a pocket knife because it is dense, but it’s also workable and rebounds better than the fiberglass. Some say a circular saw with the blade reversed works well and Brian is always psyched to experiment with power tools. The glass fibers are laid in a horizontal sheeting pattern that tend to flatten. The cotton is baked into a more three-dimensional, random pattern that lets you rip off a piece, stick it behind an outlet then fill around it and they all seems to fuse together. Plus you’re not completely freaked out by ripping it apart and seeing fibers fly. The final advantage to the cotton, although questionable, is its soundproofing qualities. We see it’s used in theaters, museums, recording studios, and has good STC and NRTC acoustic ratings as reported by the manufacturer. For standard 2×4 wood and drywall construction, the cotton manufacturer touts an STC rating of 45 versus a self-reported 38 for Knauf fiberglass.

THE LEAN PART
We’ve come up with three estimates for insulation. All assume R38 fiberglass batts on the roof and in the attic. We assume R13 fiberglass between 2×4 interior walls. We’re using R21 cotton with a radiant barrier between floor joists where we have the radiant heat. The difference is the exterior walls.

1. Option 1: $2500. R19 fiberglass Knauf Ecobatt in exterior walls
2. Option 2: $3600. R19 UltraTouch cotton in exterior walls
3. Option 3: $4900. R19 Icynene spray-foam in exterior walls

We’re wavering…and wondering: where are real reviews of these products?! On blogs, in magazines and green building sites: it’s all manufacturer’s marketing repeated over and over again! Has anyone ever used this stuff? Have you had any problems? Ever peaked in your walls to check on your insulation’s performance? Is the cotton just a feel-good story with pictures of happy blonde children hugging denim batts like stuffed animals? Fiberglass is a time-tested product. Cotton is leftover scrap from a mexican denim factory. But our insulation face-off in the garage may have some merit: it appears to seal the cavity better, it seems to sound quieter. I don’t believe that R19 is a solid indicator given all the potential leaks and kinks in a real building. They used the cotton in the new Platinum LEED Academy of Science building in San Francisco. I imagine they had the time and resources to really research the options. Is it worth another $1000?