Why are roof types important for rainwater harvesting?
The rooftop is the first step in the rainwater harvesting system. And every touchpoint of the rainwater is very important in the process to maintain quality water. Certain roof types will cause a rainwater harvesting system to fail.
So to answer the question of does roof type matter? It most certainly does. And this is another reason why it’s very practical to have a rainwater harvesting system installed while the home is being built.
Roof Contaminants: According to ARCSA, contaminants that come from some roof types include: chemicals, algae, herbicides, arsenic, and more.
Water Loss: There can be a slight loss in rainwater collection depending on which roof type. This is only found because no matter what surface you have, not ALL the rainwater is going to flow off the roof, some will stay on top and eventually be evaporated in light rains, and some will be discharged in the prefilter stage. Usually between 5-%10% annually.
Roof Types for Rainwater Harvesting
Here is a list of the most common roof types and if they can be used for rainwater harvesting. Included are some of the effects of using these types of roofing for rainwater harvesting, according to ARCSA.
- Tin – Tin is one of the best rainwater harvesting roof materials to have on a project. There is very little water loss with tin (Around 5%), and no worries of contaminants leaching out from the tin with an approved NSF-61 coating.
- Asphalt Shingles – Many shingles work with rainwater harvesting. The problem is that some shingles can leach off certain contaminants into the water, causing the rainwater system to fail, even for irrigation only. But there are shingles that do not leach these contaminants. Be sure to speak with a rainwater harvesting professional before using shingles on a house that you would like to use rainwater harvesting. Shingles usually have a water loss of about 8%-10%.
- Clay Tiles – Clay tiles can be used with rainwater harvesting. Not quite as efficient as tin (around 8% loss), but still works well.
- Ceramic – Ceramic roofing works with rainwater harvesting.
- Cement – Cement roofs can be used with rainwater harvesting.
- Rubber – Rubber roofing works with rainwater harvesting.
- Wood/Cedar/Shake Shingles – These can be used for rainwater harvesting systems that are for irrigation use only. These tend to leach contaminants and retain mold and algae which make it impossible to use for whole-house potable use.
Any shape of a roof that rainwater can be collected and diverted from should be usable. If the roof is designed to be used as a deck, where there will be lots of foot traffic and presence of other contaminants, the roof may not be usable for rainwater harvesting.
Best Practices for Rainwater Harvesting Roof Concerns
According to ARCSA
- Select roof material that matches the end-use of the rainwater. Water that is used for potable purposes is very different than water just for irrigation.
- Do not use coatings on the roof such as biocides, algaecides, and fungicides. This can harm the growth of the natural biofilm inside the storage.
- Trim tree branches from overhanging the roof, this reduces the number of contaminants that fall on the roof.
- Keep the roof and gutters from being overrun with leaves and other debris.
For every rainwater harvesting system, there is a lot to consider. Choosing the correct roof can make a major difference in your rainwater harvesting system. If you want help determining which roof type would work best for your application, contact our team.