Zinc Roofing Run-off
wwarchitect
| Posted in Green Products and Materials on
We are building a boathouse and considering a zinc standing seam roof. Because the run-off will be deposited directly into a lake, I’m researching levels of contamination that find their way into run-off from different roofing materials. Untreated galvanized steel is obviously out of the question, but I am getting mixed reviews on zinc – does anyone know whether run-off from a zinc roof would be more detrimental than from a painted steel roof?
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Replies
Wendy,
My metallurgy may be wrong on this point, but I'm under the impression that galvanized steel is nothing more than zinc-plated steel. The top layer of a galvanized steel roof is zinc, so I don't know why the run-off from a galvanized roof would be any different from the run-off from a zinc roof.
By the way, who makes zinc roofing?
It is my understanding that when galv metal roofing is not coated (say with a powder coated finish) that the heavy metal in the run-off is high, and so is not good for rainwater catchment without a first flush diverter or for irrigation. Zinc roofing is made by Rheinzink (German) and VMZinc (French). From what I have seen, these companies claim that the zinc that is released from their roofing is minimal and within safe limits for plants, animals and humans. Your question brings up exactly my quandry - what makes a zinc roof different from galvanized, in terms of this issue? I have calls in to both companies for their input.
You could use plain steel corrugated metal, concrete or clay tile, wood shingles or shakes.
My guess is that a painted, galvanized steel roof will go a very long time before the zinc starts to wear off, but I could be wrong.
Three relevant papers:
Is Rooftop Runoff Really Clean?
Roofing Materials’ Contributions to Storm-Water
Runoff Pollution
Roofing as a source of nonpoint water pollution