The Walden Effect: Farming, simple living, permaculture, and invention.

Best roofing material for rainwater collection

Cutting flashing

Long-time readers will notice that we went back and forth several times on selecting the roofing material for our starplate coop.  Part of the issue is that the roof is made up of five triangles, which means that normal metal roofing panels would be difficult to install.  But we also spend some time considering which roofing materials would work well with rainwater collection since we plan to gutter the coop and then use the collected water for chicken drinking water and a small duck pond (frequently emptied).

Rain barrelThe consensus on the internet about the safest roofing material for rainwater collection is...there is no consensus.  The most definitive study, "Effect of Roof Material for Water Quality for Rainwater Harvesting Systems," found that the first flush contained the majority of both the microbial and chemical contaminants, but even after the first flush, water contained more turbidity, total coliform, fecal coliform, iron, and aluminum than is recommended by the EPA for drinking water.  Water was tested from metal, tile, asphalt fiberglass shingle, cool roofs, and green roofs.  "None of the roofing materials emerged as clearly superior to others in terms of the quality of the rainwater harvested after the first flush," the study's authors wrote, although they felt that the green roof and shingles produced water that would be problematic if treated with chlorine.

On the other hand, other websites veto shingles for rainwater collection, even if the water is only being used on your garden.  The biggest concerns seem to be copper, zinc, lead, chromium, arsenic, and polyaromatic hydrocarbons leaching out of the shingles, although the grit that comes off the shingles is also an annoyance in ran barrels.  Other roofing types that some websites recommend avoiding include galvanized metal (which sheds zinc), any kind of roofing treated to prevent moss growth (which sheds copper), and flashing made of copper or lead.

In the end, we settled on aluminum flashing because it's relatively cheap, is easy to work with on oddly-shaped surfaces, and probably won't hurt our chickens.  If they all come down with Alzheimer's, though, feel free to say: "I told you so."

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About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.

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I drink from aluminum cans and eat foods cooked in aluminum pots occasionally. I don't think that there is much harm in it. And it is such a forgiving metal to work with. Almost as easy as corrugated steel- but that would be a beast on a roof made of five triangles.

Comment by Eric in Japan Tue Mar 25 11:26:21 2014

I didn't see cedar shingles in your list. Is that because of cost? Complexity? Some reason I haven't thought of?

I've also been playing with the idea of a reclaimed slate roof on a small shed. I'm hopeful that by keeping it small, I can keep the cost and weight down (and be able to do the installation myself)

In any case, thanks for the great progress shots as this came together

Comment by Dominic Tue Mar 25 12:22:54 2014
Did you come across any data on enameled metal? That's what we went with, filters on the other side, obviously before use, but from our research, and this was some time ago, enameled metal was the cleanest overall. I'm curious if you found any mentions of it.
Comment by c. Tue Mar 25 13:09:17 2014

@Eric: aluminium (and steel) cans are usually coated with epoxy on the inside to prevent corrosion.

@c.: "baked enamel" might not be what you think it is. Enamel used to be the name for a glass coating on ceramics and metals. But in modern roofing metal it usually means a PVDF coating (kynar 500 / hylar 5000). PVDF is a plastic that has been made corrosion-resistant by replacing half of the hydrogen atoms with fluor. It is a "relative" of the PTFE coating on non-stick pans.

Comment by Roland_Smith Tue Mar 25 14:44:29 2014

Dominic --- The article I read was very down on wood because it often comes impregnated with copper to prevent the growth of moss. However, if you could find shingles without the copper, I'm assuming it would be similar to other roofing materials. Slate, on the other hand, is usually considered one of the very best for rainwater collection.

Roland --- Thanks for chiming in! That makes enameled metal look much less enticing for rainwater collection.

Comment by anna Tue Mar 25 15:01:10 2014

You said that the runoff from green roofs and shingled roofs would be a problem if you sanitized with chlorine... is that a typo or would adding chlorine really mess that water up? Thanks for the clarification.

Comment by Lincoln Tue Mar 25 17:02:39 2014

@Anna: An admittedly cursory reading of the report you linked to indicates to me that PVDF coated steel roof seemed to perform better on most tests than other roofs, compared to the ambient rain values.

The most general conclusion that I would draw from the report is that rainwater needs treatment before it is good drinking water.

Comment by Roland_Smith Tue Mar 25 17:31:45 2014
Lincoln --- There are certain organic compounds that can be in water that interact with chlorine and produce harmful byproducts. Thus the issues with green roofs and shingled roofs if you plan to chlorinate.
Comment by anna Tue Mar 25 20:49:53 2014
Choosing the material for your roof can be a really tough job. I have experienced it myself. But we did not have a water harvesting plant so there wasn't the health issues that bothered us. Finally fed up of the confusion we went to custom roofing contractors in Toronto, Roof Lines East Inc, who suggested cedar. We agreed and our roof looks just great.
Comment by Reece Coles Sat Mar 29 02:27:54 2014
interested to know what you might think about Polycarbonate corrugated roofing such as Suntuf or DynaGlas.
Comment by JJ Mon Sep 5 08:57:25 2016

Did you research clay tile or bamboo roofs? Since there are pots made of clay I would think that it is a save material to use. What do you think?

Laura B

Comment by Laura Baiamonte Sat Sep 2 23:43:26 2017

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