The rise of the blue roof

In many cases, starting with a relatively flat roof is a prerequisite. Most design/construction professionals are familiar with the widely accepted, code-required minimums of slope (i.e. ¼ in. per 12 in.) for built-up (BUR) or membrane roofs. However, material and technology improvements are slowly changing the game. Equipment can also be elevated and structured above the roof surface to function independently and ultimately limit the importance of rooftop plane geometry in blue-roof design. Tray geometry can also be designed and adjusted to the existing roof geometry in order to accommodate varying rainwater levels in a stable, reliable way.

Blue-roof systems also need to be designed to address water-borne bacteria, insects, and plant material that often grow in standing water. Especially in certain regions, mosquitos and bacteria, like algae, thrive in stagnant water with a high pH. In many parts of the world, certain bacteria and mosquito growth can quickly become significant health issues. (In some parts of the world, designing for locales with mosquito-breeding issues is paramount in order to avoid a true public health crisis. Special additives like biological mosquito controls, sometimes referred to as mosquito dunks, are now widely available and safe for fish, wildlife, and human populations.)

Diseases caused by some bacteria, however, are preventable simply through proper water filtering. Water-carrying organisms like Salmonella typhi, E. Coli, and Legionella must be specially treated by high temperature (or other means) to ensure the water is safe for human handling or even consumption.

Even for non-potable uses, water captured in blue-roof systems must be routinely checked for purity and contamination. Simple algae growth or leaf-debris buildup can cause pesky blockages and also further contaminations by fouling valves and disrupting water flow. Water must be able to consistently turn over, flow, and move. Many roofing materials have long been susceptible to moisture as evidenced by the growth of mold—blue roofs will require professionals to pay even closer attention to these roofing hydrology lessons learned in the past.

Materials will need to incorporate bacteria-, mold, and algae-resistant technologies. Architects and engineers must be savvy about the use of new materials, water flow, and new structural geometries. One example of the necessity for innovation in this new technology is the need to find ways to construct tanks and trays with techniques specially designed to prevent water leakage. Looking to cross-disciplinary practices and exploring the use of fabrics and fibers employed in boat manufacturing, for example, is one of the ways designers can transfer technology from one industry to another to find viable solutions.

New equipment and materials must inevitably be economical, durable, and able to stand up to the elements, particularly in severe climates. In places like Florida and Louisiana, where structures are susceptible to high winds, high rainfall, and storm surge, blue-roof applications will need to be additionally sturdy and adequately structured to withstand such extreme weather conditions. Similarly, owners, engineers, and designers seeking to construct blue-roof projects in seismically active areas like California will need to take additional precautions, including structural dampening, to ensure systems can withstand the maximum shaking that can occur during the most extreme seismic event projected for that region.

In the future, blue-roof technology seems poised to become an integral part of the sustainability approach not only in the hard-surfaced, urban areas of North America and Europe, but also in the rainiest countries of Southeast Asia, Australasia, and Africa—all places where rainfall collection will be of sincere financial interest to future populations. Around the world, all cities will require new ways to deal more responsibly with rainwater-runoff collection.

Particularly as climate change continues to influence and alter precipitation levels in new ways, governments and the global building and business communities will increasingly need to cooperate to address stormwater management and water reuse. Collectively, they must act in greater and more responsible measure to accomplish sustainability goals.

Sustainability is quickly proving to be less ‘a responsible choice’ than it is an obligation. All communities will have to adapt building practices to be successful stewards of this Earth. Blue roofs will simply be another tool in the toolkit.

John Engle is the sales director at PHP Systems/Design, an engineer and manufacturer of innovative, high-performance roof pipe and equipment support systems. With 13 years of experience in roofing, he is extremely knowledgeable about the industry’s best practices and current trends. Previously, Engle worked in the pipe support and roofing industries; he is an active member of the Refrigerating Engineers and Technicians Association (RETA). He can be reached via e-mail at

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