Jun 29, 2014 5:13:53 PM
An article in Wired back in 2008, compared the environmental costs of buying a new Toyota Prius with buying a second-hand car. Their conclusion: Because a used car has already “paid off” its initial carbon cost, buying an old, energy efficient model is more eco-conscious choice than purchasing a new hybrid.
The author notes that making a Prius requires 113 million BTU of energy, equivalent to about 1,000 gallons of gasoline. So buying a Prius only makes sense if you are replacing a real gas guzzler. Otherwise, you’d be better off buying a fuel efficient used car that’s a few years old.
Better than a Hybrid? Yes, if you keep the driving to a minimum.
But as is often the case when assessing ecological impacts, getting the full picture is tough. Another, more recent study at MIT (link below) notes that the lifetime energy impact of a vehicle accounts for about 75 percent of its overall carbon emissions, and producing that fuel adds another 19 percent--which means that only 6% of vehicle's overall lifetime CO2 impact happens in the manufacturing stage. That figure is EXACTLY what I would have expected.
Why? Because it's the same for new housing. The "footprint" of the materials used in a home quckly become almost insignificant, because, as the NAHB reported about 20 years ago, the heating, cooling and maintenance of a home typically amount to 94% of its CO2 emission over its lifespan. That's why insulating, and using durable materials (that don't need much maintenance) is more important than the initial impact of those bricks or vent fans.
Jun 24, 2014 8:13:16 AM
IT'S EASY to estimate the "center of wall" R-value of various types of insulation (see chart below). But if you're a homeowner or landlord, planning to remodel, however, don't assume that simply installing a higher r-value of insulation will give you the best possible performance. It's actually possible to put TOO MUCH insulation in a cavity, and start losing efficiency. You will also want to consider air leakage through the wall or ceiling and around the windows.
Also, sometimes you can save money and get excellent performance by combining different types of insulation. There are even some hybrid systems that help you airseal at the same time you insulate. Owens Corning has a system called Energy Complete that we've featured a few times.
How much difference does air sealing make? Air leakage in homes accouont for up to 35% of overall heating/cooling costs, and unless you are using a sealing system such as the one just mentioned, or the most expensicw, closed cell spray foam, chances are good that you will need to address air infiltration with sealants, housewraps and other products.
Also: The best insulated buildings not only fill cavities with insulation--they account for what are called thermal breaks--places where heat travels through wood 2 x 4s or other structural sections that are not protected by insulation at all. Passivhaus construction, imported from Germany, demonstrates how to address this problem.
Jun 23, 2014 7:17:00 PM
WHILE DOING SOME RESEARCH on fresh air intake for wood boilers, I found this fascinating illustration of a do-it-yourself fresh air return. I haven't tried building one myself, but it looks like it might just work as a low-budget way to provide the "makeup" air a wood burner needs and maintain healthy indoor air. And conveniently enough, there's a company that sells miniature heat exchanger "coils" and pipe lengths that will allow you to build this Rube Goldberg-looking contraption quite easily.
Jun 20, 2014 6:49:22 PM
A FEW YEARS BACK, I wrote an article called "Building Blind," that exposed some major flaws in the way products are installed in new homes, with no regard for how one product limits the lifespan of another. For example, putting thin asphalt felt (tar paper) under clay roof tiles means you will have to remove those tiles when the paper fails in about 20 years, whereas the tiles might have lasted for centuries.