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Raindrops and Rooftops

Aerial view of buildings with 14 roofing panels in center.
Aerial view of roofing materials study in center of photo. Washington Department of Ecology.

Rooftops are everywhere there are buildings. They are made from metal, wood, asphalt, plastics, and combinations of the above. Researchers are studying roofing materials to determine if some toxins found in Puget Sound are coming from roof runoff. They’re especially interested in the zinc, cadmium, arsenic, copper, and lead, along with polycyclic aromatic hydrocarbons (PAHs) and phthalates, found in roofing materials because of their harmful impacts on the environment and aquatic organisms.

There have been no controlled studies of toxin presence in roofing materials under the unique climatic conditions of western Washington – where low intensity rain events last from October until June. So, beginning in 2011, the Washington Department of Ecology, Washington State University, the Washington Stormwater Center, roofing industry members, and other stakeholders, joined in a collaborative study to better understand the environmental dynamics of rooftops.

Model Rooftops

Instead of using existing rooftops, researchers constructed eighteen, 4’ x 8’ panels to model actual roofs. They were set at typical slopes used for residential and commercial buildings. The model roofs were constructed of the most common types of roofing materials used in the Puget Sound area.

View of roofing panels (resemble large lawn chairs) with captions.
14 roof panels were constructed for a study on contaminant release from roofing materials. L. Rozmyn.

In all, 14 types of roofing materials were tested, along with glass panels, used as a control. Runoff was collected in Teflon gutters and channeled into stainless steel containers to avoid contamination. Testing was done during 28 rainstorms in three rounds (2013, 2014 and 2017). The panels were originally installed at the Department of Ecology in Olympia then later moved to WSU Extension in Puyallup with the same orientation.

Many of the residential roofs and three of the commercial roofs leached metals during runoff. Seven of the roofs leached metals in measurable amounts (Figure 1). Arsenic, copper and zinc were detected in 69-100% of samples.
Some of the factors that affected metal leaching included materials composition, age of the materials, acidity of the rain, and the duration, amount, and intensity of rainfall.

Figure 1. Roofing materials tested highlighting those leaching more.

Chart showing results of study


Standard asphalt shingles were found to be low-leaching, which is good news since they account for more than 70% of the roofs in Puget Sound. However, asphalt shingles containing time-released copper granules for algae resistance, which are becoming more prevalent in Puget Sound, release low concentrations of copper over long periods of time. Many studies have shown copper can also harm aquatic life. For example very low concentrations of copper can disrupt a coho salmon’s ability to smell, by which they detect predators and return to their spawning grounds. Roofs made of copper, galvanized alloy, treated wood shakes and treated asphalt were the least environmentally friendly, having increased metals in the runoff.

For those roofing materials that released the most arsenic, copper, and zinc, researchers estimated the percentages of the metals released from roofs across the Puget Sound region (Figure 2). The calculations were based on an Ecology 2011 study that estimated roofing types across the region. These estimates can help homeowners decide what products are less environmentally harmful.

Figure 2. Relative percent of arsenic, cooper, and zinc released by roofing types in the Puget Sound region.

Researchers concurrently studied several aquatic species and learned that some chemicals in the runoff from roofing materials result in sub-lethal to lethal effects. For example, Zebra fish, have shown developmental impacts to their eyesight, body length, and in the heart area after exposure to roof runoff.

Treating runoff

The toxins in roof runoff can be treated (reduced or removed) before going into a storm drain and being discharged into nearby surface waters. Consider where the downspouts discharge the water. If they discharge to a driveway or other hard surface, then that runoff can more easily make it to a stormdrain then to nearby waterways untreated. However, if they discharge to a lawn, rain garden, or swale, then contaminants may be removed by the soils and plants, by the water soaking into the ground.

Treatment is especially important for new installations of roofs with copper time-release granules, unpainted galvanized metal or metal alloy, copper, and treated wood materials. As roofing materials age, concentrations of metals released may decrease, or increase in some cases, over the life of a roof.

Work is just getting started on studying roofing materials. Since a roof can last 10 – 30 years, more research is needed to better understand the environmental effects of aging. Will algae-resistant asphalt shingles that incorporate time-release, copper granules to resist the growth of algae continue to leach toxins? Will painted metal roofs begin to leach more as the paint wears off? Other questions include, what happens when homeowners apply roof treatments? Do toxins reach surface water in concentrations high enough to cause harm to aquatic life? How do the materials in other roof components such as gutters, downspouts, flashing, ventilation, and HVAC systems interact with roofing material?

The rooftop researchers are on top of it. Visit the Washington Stormwater Center website for more information.


Ecology. 2011. Control of Toxic chemical in Puget Sound Phase 3: Primary Sources of Selected Toxic Chemicals and Quantities Released in the Puget Sound Basin. Washington State Department of Ecology, Olympia, WA. Publication NO.11-03-024.

Ecology. 2013a. Quality Assurance Project Plan: Roofing Assessment – Investigation of Toxic Chemicals in Roof Runoff. Washington State Department of Ecology, Environmental Assessment Program, Olympia, WA. January 2013. Publication No. 13-03-105.

Ecology. 2013b. Addendum to Quality Assurance Project Plan: Roofing Assessment – Investigation of Toxic Chemicals in Roof Runoff. Washington State Department of Ecology, Environmental Assessment Program. Olympia, WA. November 2013. Publication No. 13- 03-122.

Ecology. 2014. Roofing Materials Assessment Investigation of Toxic Chemicals in Roof Runoff from Constructed Panels in 2013 and 2014. Prepared by Nancy Winters, M. McCall, and A. Kingfisher, Washington State Department of Ecology. Publication no. 14-03-033.

McIntyre, J.K., N. Winters. L. Rozmyn, T. Haskins, J.D. Stark. 2019. Metals leaching from common residential and commercial roofing materials across four years of weathering and implications for environmental loading. Environmental Pollution. Volume 255, Part 2.

Rozmyn, L. 2017. The Science of Stormwater: Chemicals in Roofing Materials. Washington Stormwater Center.

Winters, N., L. Rozmyn, J. Stark. 2018. Roofing Materials Assessment: Investigation of Toxics in Roof Runoff at the Washington Stormwater Center. Washington Stormwater Center.