We are considering using pressure-treated cedar shingles/shakes for our roof. Is that a good idea? Are there environmental problems with using pressure-treated cedar? Are these worse than the preservatives that we would have to use on the roof if we didn't use it?
This is an interesting question.
I'll be honest. I had no idea that you could buy pressure-treated cedar shingles. Southern yellow pine, yes, but I thought cedar came to you in its natural form. The heartwood of cedar is highly resistant to decay all by itself. But it turns out that manufacturers do offer shingles that have been pressure treated with a compound called chromated copper arsenate (CCA) to extend the life of this hardy species.
While until the end of 2003 it was the dominant wood preservative for residential building products, CCA is rarely used these days. Up until then CCA treated millions of outdoor decks and playgrounds. It is highly effective, but has made many people nervous because it contains arsenic (a known human carcinogen), chromium, and copper.
Concern over the chemicals leaching out of the wood and becoming a health hazard, especially to children, has made CCA-treated wood next to nonexistent. The Environmental Protection Agency (EPA) worked out a deal in which producers agreed to make CCA-treated wood off limits for most residential purposes. It was subsequently replaced by other chemicals, such as alkaline copper quat (ACQ), which is what you'll probably find in your local lumber yard.
But roof shingles and shakes weren't affected by this agreement, probably because people don't typically come into contact with roof shingles.
And the stuff must work. Fraser Cedar Products, a Canadian manufacturer, says it won't warranty its shingles in the Northeast, Southeast and Northwest unless they're CCA treated. The guarantee is for 30 years and treatment increases the cost of shingles by only about 10 percent.
If the idea bothers you, look at alternatives. Would arsenic and chromium slowly leach out of the shingles on your roof? You'd have to guess they would. But the question is whether the runoff would pose any real risk to people, plants, animals, or water.
I haven't come across any studies that would give you a definitive answer. But because CCA-treated shingles were exempt from the 2003 deal, the government is implying a low risk.
Still, if the potential risk bothers you enough, there are many other roofing options to consider.
Slate, metal, recycled rubber, and even some brands of asphalt composition shingles all will last just as long as cedar, and none are treated with CCA. Recycled rubber is especially attractive from a green point of view, and the shingles look very much like slate. You could always use untreated cedar and let the roof weather naturally.
There is no perfect answer to your dilemma. If chemically-treated building products make you uncomfortable, choose something else. If you love the look of cedar and can accept what's probably a low health and environmental risk, these shingles are appropriate for your house.
An accomplished woodworker and carpenter, Scott Gibson is the former editor of Fine Woodworking magazine, and a former editor at Today's Homeowner and Fine Homebuilding magazines. He also is former managing editor of the Kennebec Journal, a daily newspaper in Maine.