Why is slate able to be recycled?

Take a look at this excerpt from Gordon Bock's article, "From Prosaic to Precious" in Period Homes magazine.



Slate Roofing Another recycled building material at home on period houses — and in the same league as tile — is slate. Whether new or used, the life expectancy of roofing slate is determined by the source from which it was quarried. According to Jack Jenkins at the Durable Slate Co., based in Rockville, MD, "Most of the slate we see is from the slate belts in Vermont and New York State, which last about 125 years." He explains that slates from Buckingham, VA, have a life of around 175 years, and Pennsylvania HardVein and Peach Bottom slates (which are no longer quarried) stand up for 100 and 200 years respectively.
"When we reclaim slate from a building, we research the slate type, as well as when it was quarried and installed," he says, "so we have a good idea of the kind of life that can be expected from a new installation." As an example, he says they usually do not even reclaim Pennsylvania blue-black SoftVein slate because its life of 60 years or more is comparatively short. "In fact, some of the high-end slates are hard to find because, having such extraordinary lifespans and durability, they do not come onto the recycled market."
According to Jenkins, the majority of the recycled slate market is for additions to existing slate roofs and major repairs, especially when a match in appearance and longevity is desired. "Slate is a rock, a very long-lived rock," he says and, echoing tile, "what typically fails on a roof is not the rock but the underlayment." However, he says that they also regularly sell recycled slate for entire new roofs." What drives the choice of recycled slate over and above aesthetics? The opportunity to keep the roofing out of a landfill is a factor for some clients but the bigger appeal is usually the bottom line. Installation labor is the lion's share of the cost of any slate roof, old or new, but Jenkins notes that using recycled slate can contribute a significant savings on materials — as much as 30% over new slate.
For all of the above reasons, Jenkins says, "There is a pretty strong market for recycled slate," with his company keeping an inventory of some 800,000 to a million pieces in stock. Also, he says they are tapped into a national network that makes it possible to source pretty much any slate desired, from graduated slate to green, purple and mottled slates and the always hard-to-find red.
In another bit of roofing déjá-vu, Jenkins adds that the recycling process is actually an advantage. "Because recycled slate is being handled quite a bit during the course of recovery, sorting and shipping, you are getting a pretty solid material by the time it arrives at a new installation site." As with any building material, when ordering new slate you have to factor in some overage for waste. "It's the same for recycled slate," he adds, "but maybe only by a couple of percentage points more."
When it comes to installations, Jenkins says that in the hands of an experienced roofer, there are no significant differences between installing recycled slate versus new slate. "However, we have been encouraging people to consider the hook system rather than using nails." As he explains, hooks have been used for generations in Ireland and Wales. "Typically, under-nailing or over-nailing is one of the major sources of problems in slate roofs," he says, either causing breakage of under-slates or punch-through on over-slates, "and the hook system eliminates that possibility."


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