The roof of the institute needs to be replaced. The old sawn cedar shingles have reached the end of their use-life. At first glance, wooden shingles might not be the intuitive choice for the ecologically minded, but let’s take a deeper look.
The Usual Material
The standard roofing material in the US is asphalt shingles. Manufacturing asphalt shingles from new materials (fiberglass, asphalt binder, aggregate, and filler) results in 0.19 metric tons of carbon dioxide equivalents per short ton of shingles. This is the entire month’s emissions from the average American for enough shingles for a 2800-ft² roof, which would cover a 1500-2000 ft² house.
Then of course the shingles must be transported to the build site. Once installed, they would last for about 20 years. After that, they enter a landfill, or can be recycled into new shingles if one can find a place that will take them. Over their lives, 1,332 lb of carbon emissions can be expected for each square foot of asphalt shingles.
This many shingles would cost about $2100 (at $75 per square, which measures 10 × 10 ft).
To cover the same 2800-ft² roof with wooden shingles, one would need about 30 linear feet of tree trunks between 24 and 36 inches in diameter. This would be one large cedar or two oak trees. Each 36-in oak tree would sequester about 40 lb of carbon per year. By turning it into shingles, all the carbon that it has sequestered over its life will not return into the atmosphere, but rather remain in the singles. By cutting these trees down, we are reducing the amount of carbon taken out of the atmosphere each year, but not by much and it can be offset by planting young trees with high carbon appetites.
The trees must be cut up, made into shingles, and transported, all of which have high- low-carbon options. If a nearby tree can be cut down by axe, cut into rounds by crosscut saw, split into shingles with wedges and a froe, almost no greenhouse gases will be emitted other than one’s labored breathing. On the other hand, a far-away tree can be cut and sectioned by chainsaw, transported by truck, and turned into shingles in a factory (guess which way we’re going to use making shingles).
At the end of its life, which can be up to 40 years for properly installed oak shingles or 20 years for cedar ones, the shingles can be composted. Over those 40 years, those two oaks would have sequestered 4 tons of carbon or 1.4 lb per square foot of roof (assuming trees were not planted to replace them).
To make these shingles by hand would require 5–10 hours to prepare the rounds and about 30-40 hours to make the shingles. To purchase cedar shingles, it would cost $5600 ($200 per square). I can’t find oak ones for sale, even though they are the standard in other parts of the world, but as they last longer, they may be worth more.
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