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Metal roofing for rain catchment

 
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In searching for roofing for an RV tiny house conversion, I noticed a lot of metal roofing has prop 65 California warnings. I’m aware of the dangers of burning, welding and hot cutting galvanized, but is it safe for cantact with rain water? Anyone know of a way to find the exact ingredients used in the zinc coating or if it’s safe?
 
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Hi Ivanson,

Is galvanized the only option? Rain water has a very low PPM, so its prone to pick up contaminants; however, I'm not sure if better options exsist for tiny house roofing, as even painted tin sheets will most likely have some unwanted contaminate. The good news is the water is only in contact with the roof for such a short period on time, it reduces chances of contaminate diffusion into the water. You'll also need to filter and or treat the water collected anyway, as roofs tend to catch the occasional bird dropings amongst other things. So maybe a good carbon filter set up, will help eliminate any of those concerns about contaminants in the tin coating. Galvanized water troughs are used in animal husbandry, so hopefully it doesn't leach to many contaminants; however, I've never personally researched it compared to the enamel paint coatings.

Im sure a good on online search from reputable sources concerning the spacific coatings in question, will yeild reliable results for proper comparison, so you can better weight your options.

Hope that helps!

 
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Sorry I don't have an answer for this, but I just wanted to chime in and say great thread/question. Everytime I see a roof water catchment system this always comes straight to mind, and what especially gets me is that many people also have solar pannels on their watercatchment roofs... and I just can't help but guess that could be very bad... but perhaps I'm wrong?


Perhaps a natural wooden shingle roof?
 
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You'll undoubtedly get various views on this topic.

Notwithstanding air pollutants and dust residues on the roof, rain is perhaps the most pure form of water you'll get.

You can attach a first flow diverter that dumps the first fall of rain e.g. With all the stuff that has accumulated on the roof since the previous rain.

New galvanised tanks tend to make the water taste a bit 'tinny' for a while, but as the ecology of the water changes, it loses the taste altogether.

Galvanised roofing, guttering, pipes and tanks have been used here for well over 150 years without any problems. The modern tanks apparently have a thin plastic film these days, though I'd rather bare metal to some type of synthetic shit in my water supply.


 
pioneer
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The solar panels should not bother your water, mine and others I have seen are glass on the outside so nothing that is going to affect the water
 
pollinator
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Yeah, I think solar panel water collection is probably a better bet than off of galvanised.

Any time this topic comes up, I am reminded of an entry in a Canadian Home Reference Manual I once chanced upon while cutting the job down and collating it together in sets. It was on gutter and roofing component lifespans. By far, the longest-lived roof components were actually made of copper or brass. Short of mechanical damage, only the degradation of the components those parts were attached to would cause them to fail.

Among the longest-lived roofing systems was slate tile.

I would consider these to be great options, though expensive and niche, but I think each had a lifespan rated 50+ years. My practical alternative to these is that raised-seam baked-enamel steel roofing that you don't puncture in the assembly. I especially like that most systems nowadays size things so that some sizes of solar panel fit cleanly between the raised seams.

One idea I had the last time I cleaned out my parents' rain gutters was that a rain gutter would be an excellent place for a coarse biochar filter, perhaps with a coarse sand element. It may be that the downpipe would be the place for any such thing, and that 1/4" discrete pieces of biochar might be required to maintain the rate of flow, but I think the idea has merit.

Also, what about a roof-edge greenroof strip that acts as a physical and biological filter? You wouldn't want to rely on it alone, but it would be an excellent first-stage filter.

-CK
 
Chris Kott
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Oh, sorry, I got the numbers wrong.

Slate roofs can be expected to last 80 to 100 years, and longer with proper maintenance. And while copper guttering might need to be replaced after 50 years, copper downspouts can last more than 100 years.

-CK
 
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Here you cannot use rain water caught from a galvanised roof for irrigation as the zinc is considered a contaminate, but new steel roofs are not galvinised anyway. (so I can use half my barn roof for veg that will be cooked, the other half is old galvanised sheets and the house is asbestos)
 
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To find the exact formulations used on your roof, you'll need to look go the manufacturers website, and from there maybe go to the coating manufacturers website.

For example, my metal roof was made by Midwest Manufacturing. In the "Cool Chemistry" pamphlet, they list that the coatings are mainly 70%PVDF or silicone-modifi edpolyester.

My general guess is that after a season or two, the amount of toxic gick leaching from a modern metal roof is likely to be negligible compared to the amount of toxic gick that has been deposited onto the roof from the air.
 
Ivanson Lance
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So to clear some things up, I do plan on having a first flush system and filtering for drinking water, but I would like to have the water in my tanks free of heavy metals for bathing, washing dishes and watering plants/animals. I did a little more digging and found that galvalume is a pretty nasty coating and should probably be avoided for rain catchment, and that regular zinc galvanized coatings appear to be generally safe at ambient temperature, so much so that it’s considered safe for food contact by the fda as long is the food is nonacidic. I thought of other roofing options but galvanized seems the way to go as long as I can make sure it’s safe because it’s light weight and requires minimal framing underneath. Slate is too heavy and wood shakes would probably not survive driving down the road. Copper might be an option if galvanized is unsafe but seems like a waste to put on an rv! I think as I get closer I’ll contact specific manufacturers for the alloy in their coatings
 
Ivanson Lance
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Skandi Rogers wrote:Here you cannot use rain water caught from a galvanised roof for irrigation as the zinc is considered a contaminate, but new steel roofs are not galvinised anyway. (so I can use half my barn roof for veg that will be cooked, the other half is old galvanised sheets and the house is asbestos)



Where do you live that you’re not allowed to catch water off of galvanized roofing? Is there any research that show it leaching into water?
 
pollinator
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You need to be sure of the terms you are using.
Galvanising is a process whereby zinc is applied to the surface of steel.

It is often called zinc plating, hot dipped or just galvanising.

The new coatings are called  Zincalume in Australia, and other names elsewhere perhaps
Zincalume is a premium metallic-coated steel product that consists of 55% aluminium, 43.5% zinc and 1.5% silicon, by volume.
However the entire coating is about 80% aluminium. The coating gives it a lifetime of almost four times that of galvanised steel.
It is safe for drinking water
 
Skandi Rogers
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Ivanson Lance wrote:

Skandi Rogers wrote:Here you cannot use rain water caught from a galvanised roof for irrigation as the zinc is considered a contaminate, but new steel roofs are not galvinised anyway. (so I can use half my barn roof for veg that will be cooked, the other half is old galvanised sheets and the house is asbestos)



Where do you live that you’re not allowed to catch water off of galvanized roofing? Is there any research that show it leaching into water?



Denmark you can catch it and use it for your own garden but you cannot sell anything you water with it. even if you caught the water from glass you can only use it on products that are normally cooked before consumption.
 
John C Daley
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Skandi, it would be interesting to find out how and why a law like that came into exsistance.
Sometimes good laws are created and things change.
for example in Australia, wells were banned in gardens in the suburbs because people had cess pits next door 3 Metres away.
From;Denmark bans added vitamins
Danish health officials yesterday banned the cereal company Kellogg's from adding vitamins and minerals to its famous food brands, saying they could damage the health of children and pregnant women.

Now I am not trying to denegrate Denmark, your Princess is an Aussie, but Denmark thinks adding vitamins to food should not happen.
I think it is strange., but its an example of odd laws.


 
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my wife found some to use that is safe for  catchment
 
Ivanson Lance
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John C Daley wrote:You need to be sure of the terms you are using.
Galvanising is a process whereby zinc is applied to the surface of steel.

It is often called zinc plating, hot dipped or just galvanising.

The new coatings are called  Zincalume in Australia, and other names elsewhere perhaps
Zincalume is a premium metallic-coated steel product that consists of 55% aluminium, 43.5% zinc and 1.5% silicon, by volume.
However the entire coating is about 80% aluminium. The coating gives it a lifetime of almost four times that of galvanised steel.
It is safe for drinking water



I think I would be more worried about an aluminum based coating than a zinc based one, aluminum is almost impossible to get out of your body once it gets in
 
Ivanson Lance
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cougina machek wrote:my wife found some to use that is safe for  catchment



Any way you could find out the manufacturer?
 
F Agricola
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Skandi Rogers wrote:

Ivanson Lance wrote:

Skandi Rogers wrote:Here you cannot use rain water caught from a galvanised roof for irrigation as the zinc is considered a contaminate, but new steel roofs are not galvinised anyway. (so I can use half my barn roof for veg that will be cooked, the other half is old galvanised sheets and the house is asbestos)



Where do you live that you’re not allowed to catch water off of galvanized roofing? Is there any research that show it leaching into water?



Denmark you can catch it and use it for your own garden but you cannot sell anything you water with it. even if you caught the water from glass you can only use it on products that are normally cooked before consumption.




Although there are many reasons why such a law would exist, I wonder if it's a legacy of Chernobyl? The fallout map shows dispersion patterns affecting a significant area of Scandinavia and the UK. It would be worthwhile to look deeper into the reasons particularly if purported climate change issues effect rainfall and people need to store water in the coming decades.
 
Skandi Rogers
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F Agricola wrote:
Although there are many reasons why such a law would exist, I wonder if it's a legacy of Chernobyl? The fallout map shows dispersion patterns affecting a significant area of Scandinavia and the UK. It would be worthwhile to look deeper into the reasons particularly if purported climate change issues effect rainfall and people need to store water in the coming decades.



I don't know why there are only some permitted roofing types but I do know why you cannot use it for growing food to be eaten raw. All water used to water food plants that are customarily eaten raw must be of drinking water quality, and roof/pond/ditch water is not. It leaves me in a wonderful situation of having 3600sqr ft of roof I can collect water from, a huge unused urine tank that could be repurposed (unused for 30+ years but still holds water) but using it would mean I would need two different watering systems, and some way to convince the inspectors I was keeping it separate! Fortunately I do not need to irrigate more than once or twice a year outside so it isn't a huge issue.
 
Ivanson Lance
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F Agricola wrote:

Skandi Rogers wrote:

Ivanson Lance wrote:

Skandi Rogers wrote:Here you cannot use rain water caught from a galvanised roof for irrigation as the zinc is considered a contaminate, but new steel roofs are not galvinised anyway. (so I can use half my barn roof for veg that will be cooked, the other half is old galvanised sheets and the house is asbestos)



Where do you live that you’re not allowed to catch water off of galvanized roofing? Is there any research that show it leaching into water?



Denmark you can catch it and use it for your own garden but you cannot sell anything you water with it. even if you caught the water from glass you can only use it on products that are normally cooked before consumption.




Although there are many reasons why such a law would exist, I wonder if it's a legacy of Chernobyl? The fallout map shows dispersion patterns affecting a significant area of Scandinavia and the UK. It would be worthwhile to look deeper into the reasons particularly if purported climate change issues effect rainfall and people need to store water in the coming decades.



Looks like I’m officially donning my tin hat...
https://www.google.com/amp/s/www.forbes.com/sites/jeffmcmahon/2011/03/28/epa-expect-more-radiation-in-rainwater/amp/
https://www.pri.org/stories/2011-04-08/fukushima-radiation-us-rainwater-and-milk-updated
 
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