Roofing and Rainwater Collection Systems

Going green has quickly become popular for a number of reasons ranging from ecological responsibility to revenue generation and savings. As people install upgraded weathering, siding, windows, and air conditioning systems in their homes, they tend to miss the opportunities that are open with roofing. Using a material that is recycled is a great step in being environmentally friendly. Solar systems like solar shingles will even power your home, reducing your energy costs, greatly. However, roofing systems can also collect rainwater for future reuse.

Rainwater Collection

Rainwater collection is the accumulation of rainwater for future use. Usually this occurs before the rainwater reaches your local aquifer. The system is comprised of a few basic components;

  • Catchment Area
  • Conveyance
  • Storage
  • Treatment
  • Distribution

The catchment area is the area on which the rainwater is collected, usually the roof. Conveyance refers to the transportation of the rainwater from the catchment area to the storage and is considered the gutters and downspots of a roof. Storage returns to the storage tank where rainwater is collected. In order for rainwater to be consumed it must be treated.

Many large property owners will also treat water for agricultural and ranching needs. Distribution reflects to the distribution of the collected water in the storage to its final destination or use in and outside of the home.

Several factors are thought to determine the effectiveness and efficiency of a rainwater collection system. Roofing materials, the slope of the roof, and the size of the roof are all typically considered when designing the catchment area or roof.

Roofing Materials – No Clear Winner

While newer roofing materials do tend to outperform older materials, in 2010 the Texas Water Development Board determined that the material of the roofing is not nearly as important as the contaminants it gives off. In their study they found that rainwater collected contained TC, FC, Fe, and AI, all above EPA drinking water standards.

No roofing materials stand out as the best to use in the process as far as effectiveness either. Both recycled roofing materials and "green roofing" materials give off contaminants that must be treated prior to drinking.

Slope of the Roof – Steep vs Flat

The slope of the roof is considered the "angle" of the roof in layman's terms. This angle coupled with the force of gravity on water's mass, determines the speed of the rainwater runoff. As you would imagine a flat or low slope roof will retain water when compared against a steep slope roof. However, since the purpose of the catchment area or roof is to channel the rainwater into the gutters or conveyance system, the angle or slope of the roof should be determined based on your storage capacity and needs.

The slope of the roof should also be determined in a manner that will reduce contamination on the catchment area and allows rainwater to flow unobstructed, into storage for processing.

Size Matters – Bigger is Better

Size does matter with the catchment portion of a rainwater collection system as it will be a controlling factor in how much rain can be collected. The more square area a roof has, the more rainwater can be collected. The size of the catchment area is the entire square footage of your roof.

You can determine your roof's square footage by adding the square area of ​​your home building and adding the area of ​​"roof overhang" or square area of ​​roof that extends beyond the boundaries of your home or building.

You can also estimate your harvested water by using a calculation from Texas A & M University's AgriLife Extension website;

Harvested Water (gal) = catchment area (ft2) X rainfall depth (in) x.623conversion factor

Roofs – A Passive Income Generator

Many people already realize the tremendous value of their roof whenever they step outside in a hot sun. For years people have already been harvesting the opportunities that solar energy roof systems offer. However, with a rainwater collection system, a roof can start generating revenue even when there is no sun out.

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