Insulation and Air Sealing
If we’ve learned one thing throughout this renovation process, it’s that insulation and air sealing are two sides of the same building efficiency coin. Insulation provides resistance to heat flow and air sealing reduces the amount of uncontrolled air infiltration. Our building performance advisor (and now friend), Nate Adams of Energy Smart Home Performance compares this dynamic duo to a sweater (the insulation) and a windbreaker (the air sealing). You wouldn't want to be caught out on a cold day with either one by itself. Together in a house, these features cut heating and cooling costs, increase comfort, and improve indoor air quality.
In this old house, built in 1901, we had a long way to go...to put it mildly. In our initial energy audit, the TREE House scored a blower door number of 6700 cfm. Given that we maxed out the fan, this is almost certainly a conservative estimate. Basically, this gives a measure of the rate at which the air inside a building is replaced with outside air. Nate says that a blower door number that is roughly equal to the home’s square footage ranks as "not too bad." With a square footage of about 2,000, our house was way beyond bad. In layman’s terms, it leaked like a sieve. And we had a long way to go to fix it.
The numbers are all over the place, but insulating and sealing leaks are estimated to cut a house’s energy costs by 5%-30%. Not only are poorly insulated and leaky houses more expensive, they’re also just plain uncomfortable. Drafts, fluctuating temperatures, and cold corners/hot rooms are no fun. As much as you might not want to waste money or be uncomfortable, there are other good reasons to improve your home’s thermal envelope (the building's shell that acts as a barrier to the unwanted transfer of heat or air between the outside and inside). The U.S. Department of Energy estimates that residential and commercial buildings in the U.S. account for almost 39% of our total energy consumption and 38% of CO2 emissions. In the residential sector, space heating and cooling are responsible for 52% of energy used on site, and 39% of primary energy use (energy used to fuel electricity-generating plants). To get a sense of the usual sources of air leakage, see the picture to the left (from the US EPA).
Convinced yet? We were. And we wanted to see how far we could get. Admittedly, we went beyond what a normal homeowner would need to do to achieve significant improvements. And wanting to be able to judge our improvements by official standards, we were seeking to decrease our HERS score by at least 75%. And we did! We took the house from a score of 208 (a whopping 108% less energy efficient than a standard new home) to a 45—more than a 78% reduction! According to the Residential Energy Services Network, that's over "50% more energy efficient than a standard new home and 80% more efficient that the average resale home." Here’s what we did, from the bottom up.
Our ICF foundation is extremely well-insulated and sealed, contributing to the overall integrity of the thermal envelope. (For more info, go here.)
Spray foam was used on the sill plates, soffits, and in some of the new walls. This stuff works well, but is not without problems. It’s a two part substance. Half of it is made of soy (and in Hiram!), but the other half—necessary for permanent binding—has all kinds of nasty stuff in it. So we used it thoughtfully and sparingly.
Dense packed blown-in cellulose filled the wall cavities down stairs (where insulation had settled over the years) and upstairs (where there was none!). It was also used to insulate the attic. See the picture on the left of Nate in action.
Rigid polyiso foam on the exterior has the highest R-value per inch of any insulation. We purchased our 3” layer second-hand (it once covered a building in Michigan, to see it on the TREE House, see picture to the right). In one fell swoop, we minimized resource use, diverted waste from the landfill, and gained an additional 20 R-value. Overall, our walls are now about 10” thick, and include (in order from the outside in) the new siding, furring strips, housewrap, foam, old siding, sheathing, studs, cellulose, lath, and drywall.
Insulating and sealing the attic involved a difficult decision. We had to choose between eliminating the usable space there and insulating/sealing the attic floor or keeping that space and either giving up on our overall house goal or paying nearly twice as much to achieve it. We went with the first. This involved some demo of knee walls and the edge of the floor, a layer of foam on the whole attic floor, and 18” of cellulose on top of that (see pics below). Yep, you read that right...18 inches!
After all this, we have come a long way. To date (July 2014) we have reduced our blower door number by about 85%—from 6700 to 962! That’s huge. Now that our house is so tight, we need ensure a supply of fresh air. Our Energy Recovery Ventilation system will take care of that—it’s been described as being like having an open window all year round, except one that allows you to control what comes in and what doesn’t.
Later....Our First Winter in the House
We used our first winter as a test case to see how our mini-split heat pumps did on their own—prior to connecting the radiant floor heat system in the basement. See the figure below.
You can see that, even without the extra heat source, our house stayed at a pretty constant temperature and the unheated basement held steady around 50○F while the outside temperatures dipped well below zero. Notice the significant increase in indoor temps around January 31? This was the point at which we began leaving some of our doors open so that air could circulate better. We’ll collect comparative data next year—with the radiant floor heat in place—to learn more about its effects.