Readers,
I thank you for your interest in the results of my home energy audit. I know that many of you wondered whether I have followed the suggestions made by the Energy Detectives and whether they were successful. After keeping you in suspense for two whole weeks I am finally here to answer: yes and yes.
Insulation is complicated, readers. So many kinds to choose from! There's fiberglass, cellulose, petroleum- or soy-based spray foam, denim fluff, and mushrooms. A comparison chart rating these options according to price, R-value, and varying shades of green will show you a complicated matrix of pros and cons that could give you a bit of a headache (nothing to do with the formaldehyde). Fiberglass is cheap and easy to install but itchy and not very good for the lungs of the installers, nor is it as effective as, say, cellulose or, better yet, spray foam. The very dense, closed-cell spray foam gives you a lot of bang, but for a considerable buck. Denim is kind of sexy, but what about the mice?
Before I get into the particulars of the plan for my house, let me offer a brief primer on insulation:
R-value: The basic measure of insulation's effectiveness, it indicates resistance to heat flow. A higher R-value means more resistance, i.e. better insulation. It should be noted that every building material has an R-value, but of course 1/4" plywood, with its R-value of .31, is significantly less resistant to heat than, say, [fiberglass batting, which could give you an R-value of 3 or 4 for every inch of thickness.]
Fiberglass (approximately R3 per inch): not
the favorite of energy-saving types or the health-concerned. While it's cheap, it doesn't have as much R-value as, say, cellulose or spray-foam.
As mentioned above, it is uncomfortable to work with and sends
tiny glass particles into the lungs of installers (koff, koff). It was traditionally made with formaldehyde, although this seems to be on the wane.
Apart from the health risks, it seems that fiberglass batting is less effective than other types of insulation. For one thing, when placed inside a wall, it fails to prevent air from
moving up or down through the fibers. In a balloon-frame house (like
mine), the base of a wall is open, as is the top. If you are going to
install fiberglass batting inside such a wall, it's important to seal
the wall at the top and bottom so that drafts cannot flow up or down.
Another
problem with fiberglass batting as opposed to blown-in cellulose or
spray-foam is that it cannot fill a space completely; there will always
be gaps in between bats, allowing air to flow where you don't want it to.
Cellulose (R3.5 per inch): Made from recycled paper, this fluffy material is blown in through a large tube that
comes out of a big truck. If used to insulate walls, it must be drilled and blown
into a closed wall so that it can be contained. It's blown in very densely so that it is tightly packed. If
used to insulate a floor, it can be blown into an open space and remain as
loose fill. More expensive than fiberglass, less expensive than spray-foam. Requires professional installation.
Spray-foam (R5.9 per inch): Most spray-foam is made of polyurethane, a petroleum product. It is expensive, but has a very high R-value.
Non-petroleum alternatives exist, the most common of which is made of
soy. Cheryl makes the point that while it's nice that soyfoam is not
made of petroleum, it has a lower R-value than the urethane sprayfoam,
so if you use the same amount, you will have to use more heat, which
will probably come from a fossil fuel. So there's a tradeoff, and Cheryl made the point that no
studies have been done comparing the total petroleum cost or carbon emissions of the two types of spray-foam use. She also made the point that urethane foam doesn't use that much petroleum and that, once dried, it is inert, offgassing nothing but nitrogen, which is harmless, and water.
Rigid-foam Board (R7 per inch): Polyisocyanurate board comes in large panels (pink, in my experience) that are maybe the size of a sheet of drywall. Its rigid shape makes it structurally useful and good for retrofitting; this is the stuff you see on the exterior walls of a house being built or resided.
I should note that during my first conversation
with Cappy Kidd, president of Informed Energy, he rejected my use of
the term "green insulation," making the point that no product is
inherently green; it's all a matter of using the right resources in the
safest and most efficient manner.
When devising my insulation plan, Cheryl Pomeroy and Aaron Lund, the
energy auditors, took into account my plans to renovate the attic at
some point. Currently an empty, unconditioned space, my attic housed
nothing but a furnace, a lot of ductwork, and a beautiful two-year-old
chimney (it's amazing what $4000 can buy).
The furnace would soon need replacing and it was my plan to put the new one off to the side or out in the enclosed back porch and run new ductwork under the floor, leaving the floor open and ready for renovation, whenever I could afford to get around to it. Given these plans, Cheryl and Aaron thought it would make the most sense for me to insulate the underside of the roof, even knowing that I would eventually be cutting it open to build dormers. Better, they reasoned, to condition the attic space, which I would have to do anyway once I remodeled, and keep the floors clear: any heavy-duty insulation of the floor would probably end up covering the floor, making it unwalkable. Also, it is always good to keep your furnace inside a conditioned space so that the heat it generates does not escape to the outside.
Having established that, Cheryl drew up four plans:
Option 1: Add rafter baffles for ventilation between soffit (eaves) and roof ridge (this is to prevent the gathering of any moisture, which could turn to ice in winter and damage your roof). Add 1" rigid foam board to underside of rafters. Aaron explained that it's important to cover the rafters because, being
made of wood, they conduct heat, acting as a thermal bridge. In other
words, they will let heat out or in, probably whenever you least want
it. Drill and blow in cellulose. Est. R-value: R18
Option 2: Spray-foam entire rafter cavity (spray-foam is entirely airtight and allows no condensation; therefore, no baffles are necessary). Then hang 1" rigid-foam board across the rafters. Est. R-value: R30
Option 3: Cut and friction-fit unfaced polyiso board between the rafters; carefully seal gaps and joints with spray foam so that the entire system is air tight. Then add another layer of foam board across the entire system, covering the joists. Est. R-value: R29 with 1" board; R36 with 2" board
Option 4: To be honest, I did not entirely understand Option 4, but it basically involved sistering out the joists (extending them) by attaching 2x2 boards to the existing 2x4s. This would then create more room between the joists, into which you could fit more insulation. I suppose one advantage of Option 4 is that it would allow you to increase the R-value of Option 1 by using a greater volume of cellulose, which is cheaper than spray foam. Option 4 seemed a little overly complicated, so I did not consider it for long. Est. R-value: R28
This entire project would not be cheap, especially if I went with spray foam, which is quite expensive. As with so many things, you tend to get what you pay for: the most energy-efficient solution would probably end up costing me the most money. Cheryl guessed off the top of her head that Option 2, which would give me the greatest R-value, could cost as much as $6000; Option 1 would probably cost about one-third as much.
Cheryl and Aaron left me with a list of insulation contractors that they had worked with before, complete with notes about the particular expertise as well as strengths and weakensses of each company. They both made the point
very strongly that air sealing would be every bit as important as
insulation, and that any contractor I hired should take this seriously.
Finally, they urged me to call with any questions once I started the job.
Next up: Insulation Story Part II: Execution.