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Using Metal Roofing for Rainwater Collection

Rainwater Catchment Information & Recommendations

Rooftop rainwater harvesting is quickly becoming a popular choice for both residential and commercial builders who are seeking sustainable, eco-friendly water harvesting solutions. Metal roofing provides the optimal catchment surface for rooftop rainwater harvesting systems.


Rainwater harvesting, or rainwater collection, is the process of collecting the run-off water from a structure in order to store it for later use. For the majority of rainwater collection, a roof acts as the primary catchment area. Typically, rainwater will collect in the gutters, move into the downspouts, and finally collect in a storage container. The storage container could be something as simple as a rain barrel or something more intricate like cisterns in order to supply your household with water. A roof provides a wonderful surface for this purpose, especially a metal roof with appropriate paint systems.

Rainwater collection is an important part of the LEED process to help reduce runoff volume, and improve water quality on sustainable sites. To effectively capture this water for redistribution, a collection system such as the roofing and gutter systems on a project must capture up to 25% of the water from impervious or hard surfaces. This water can then be filtered and reused in the building's sustainable water system, or released into a public wastewater treatment facility. 

Designing and maintaining metal roofing that incorporates a rainwater collection system can be simple. The design of the roof needs to be durable enough to withstand the weight of heavy rain or snow and there must be an easy path for the water to follow. Bridger Steel manufacturers a variety of metal roofing panels that will withstand all weather conditions and provide the smooth surfaces needed to make it easy to clear debris and dust.

When planning to use a metal roof as a rainwater catchment area, understanding the components that you need to consider will help lead to the success of your build.

What are the benefits of rainwater collection?

Rainwater harvesting provides many benefits to the homeowner and the environment. Here are just a few:

  • Free Source of Water — Rainwater harvesting is a completely free source of water for your home and you have complete control over the water supply. This is ideal for cities or towns with water restrictions.

  • Multiple Uses — The rainwater you harvest can be used in tons of different ways. The three basic categories rainwater can be used for are irrigation systems, indoor use, and outdoor use. Rainwater can be used for everything from washing your cars to watering your garden to refilling your fish pond.

  • Alleviate Emergencies — Whether you choose to use your rainwater collection system as your main source or your back-up source of water, it can provide your home with a large supply of water in emergency situations.

  • Easy to Use — Rainwater collection systems are very basic and easy to use. The technology used to collect rainwater is inexpensive and low maintenance. Most rainwater harvesting systems can be retrofitted onto an existing home and easily built during new constructions. They’re relatively flexible and modular, so expanding, re-configuring, or relocating the rainwater system is easy to do!

  • Environmentally Responsible — Collecting rainwater is a self-sufficient and energy-efficient move because it helps conserve water. The systems also reduce runoff water from homes and business and can help solve drainage issues while providing you with free water. Rainwater is also much better for your surrounding environment, including gardens and plants, because the water isn’t treated with any chemicals or chlorine. 

There are many, many more benefits to rainwater collection — check them out here.

Choosing the Best Roofing Material for Rainwater Harvesting

While a number of base materials like asphalt, slate or tile roofs can be used as rainwater collection catchments, metal roofs are often the preferred system. This preference has less to do with the base material and more to do with the potential contaminants that may grow on the material itself. Metal roofs are often coated in anti-microbial paint systems, and shed larger materials easily without the range of cracks and crevices for materials to adhere to.

Compared to other roofing materials, metal roofs (especially galvanized metal roofs) have much lower concentrations of dissolved organic carbon and other bacteria. This means a metal roof rainwater collection system will produce water with less of the disease-causing microorganisms. Galvanized metal roofing especially is recommended for rainwater harvesting because the panels will be coated with a later of zinc, which seals the metal panels, prevents rusting, and lowers the levels of iron in your water.

However, any rainwater harvested from any type of roof, including metal, should always be filtered and decontaminated before use. This is especially important if you will be using your rainwater collected from your roof as a drinking source or for use inside your home.

The Best Roof Slope for Rainwater Collection

The angle of your roof, or slope, will determine the speed and rate at which water will leave your catchment area. A steep-sloped roof will shed water more quickly than a low-sloped roof, along with better removing debris or other foreign materials. A higher slope also performs better as a catchment area by preventing stagnant water buildup and possible contaminants from affecting your storage.

Calculating Water Catchment

Understanding how effective your rainwater collection system will be using your roof can be determined by using the following formula:

Catchment Area (sq ft) x Rainfall Depth (inches) x 0.623 (conversion factor) = Harvested Water (gallons) 

Bridger Steel provides eco-friendly builders with the ideal rainwater catchment surface —creating lasting beauty and conserving resources with safe, easy, and effective metal roofing.

For more information or advice, contact a Product Specialist

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