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Roofing Materials for Rainwater Harvesting

I was asked the other day about what is the best roofing material for rainwater harvesting and it made me pause. I have the generic ideas once presented by others in the past but why not build upon them in a logical way and think about new solutions?

Roofing materials not good for rainwater harvesting:

Asphalt – The most common roofing material is asphalt which is not a good surface to harvest rain from. Crumbling asphalt roofing material debris can be separated during filtration but this type of shingle can also leach petroleum into the water.

Wooden Shingles – Wooden shingles are porous and harbor mold and fungus that will end up in your rainwater harvesting system. Wooden shingles are also treated with chemicals not fit for human consumption.

Metal – I remember cases of people using metal roofing materials, and then using the rain water for watering their vegetable gardens. Tests showed that the heavy metals in those vegetables were above the allowed limits. But be aware that today’s metal roofing materials do not break down as fast and there could be some that are considered safe for “potable” water.

Roofing Materials that are ok for rainwater harvesting:

Slate or Tile – Slate is a good surface to harvest rain from as long as it is kept clean. I have not heard much about this material and rainwater harvesting to be honest with you but it should work fine because it does not deteriate. Make sure you are not confusing slate with harmful asbestos tile which was mainly used as siding in the past.

Membrane Roofing Material – I have also not heard much about membrane roofing materials but in doing some quick research see that there are many products offered that are safe for “potable” water. A roofing membrane would be ideal because its chemical makeup is not friendly to bacteria. A roofing membrane could also be painted on an existing rooftop. If you are searching for this type of material just make sure it passes “potable” standards. A black rubber roofing membrane could also heat up enough to kill bacteria during sunny days.

Fiberglass – Fiberglass is a great surface to harvest rain from but it is not attractive to most people. It also is a bit noisy when it rains like the metal rooftop. If I was to build a tropical “off the grid” home I would use this roofing material because it is light weight to transport and serves its purpose well. In a more northern climate I would go a roofing membrane material.

Other Materials – People also collect rain from false roofs like tents or tarps. A large tarp can be kept clean and washed when it is not in use so the water is freer of pollutants. A tarp can also be used to cover a rooftop that would be hazardous for rainwater harvesting as a temporary solution.

I believe roofing membranes will become more popular than other materials because of their easy application. All it takes is for a couple of us to show how it’s done by covering our catchment surfaces with these high tech compounds. Remember that all rooftops are not clean no mater what material they are made from. Bird droppings and other debris will still fall and wash into rainwater harvesting systems. Also remember that a rooftop should be cleaned on a regular basis if used for potable water. Combine the right roofing surface material with first flush, course debris removal, fine debris removal and some sort of mechanical filtration system like reverse osmosis and you are “good to go”.




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Posted in Harvesting by Administrator on September 22, 2005.

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