What Is an Ecoroof?
An ecoroof is a thin vegetated roof system designed to manage rainwater. Also called “extensive green roofs,” the simplest ecoroofs are built with the following layers starting at the bottom:
- A waterproof membrane,
- Drainage material,
- A lightweight layer of soil, and
- A cover of plants.
The primary purpose of an ecoroof is to help absorb and filter rainfall. Ecoroofs provide other benefits including:
- Filter air pollutants.
- Reduce outdoor air temperatures and the resulting urban heat island effect.
- Provide habitats for birds and insects.
- Insulate buildings and lower heating and cooling costs.
- Are visually attractive.
How Ecoroofs Work
Ecoroofs are living systems with soil and plants that soak up rainwater. The rain nurtures the plants and stays in the soil instead of going into sewer or stormwater pipes. During heavy rains, when more rain falls than the ecoroof can absorb, the soil slows the flow of water into the pipes. Reducing the volume and speed of rain runoff in this way helps reduce the risk of flooding, sewer backups, and sewer overflows.
Ecoroofs are designed to filter pollutants out of rainwater and help minimize the use of conventional roof materials that can have oil or chemical pollutants on their surfaces.
Summary of Ecoroof Design Requirements
These site and design requirements can help you decide if an ecoroof might be appropriate for your project.
- Locate ecoroofs on flat or pitched structures with slopes up to 25 percent.
- Roofs must be structurally strong enough for the increased weight. A structural engineer must review plans and drawings.
- Environmental Services requires at least 4 inches of soil. Consult the Stormwater Management Manual. More soil can be installed to broaden the range of plants the system will support and to meet other stormwater management goals. But, thicker ecoroofs will need more structural support.
- Drains and downspouts must be connected to an approved disposal location.
- Avoid using copper, lead, galvanized metal, and other materials that can pollute runoff.
- Chemical root barriers and herbicides are not allowed. Fertilizers are strongly discouraged as they can pollute runoff.
- The waterproof membrane must be installed by a licensed contractor who can certify and provide a warranty for their work.
When selecting plants, keep in mind that plants should be:
- Low maintenance.
- Drought-tolerant (requiring little or no irrigation after establishment).
- Able to withstand heat and cold.
- Perennial or self-sowing.
- Shallow-rooted (to avoid damaging the waterproof membrane).
When to Call a Professional
Property owners must consult a design professional to design and construct an ecoroof. A structural engineer must certify ecoroof designs in order to receive City approval. Design professionals can use the standard configuration under the Simplified Approach in the Stormwater Management Manual.
The project may also need a plumbing permit to alter downspouts.
Costs and Permits
Ecoroofs have a higher upfront cost than traditional roofs, but property owners can expect long-term savings from ecoroofs due to reduced costs for roof repairs, maintenance, and replacement. With proper maintenance, ecoroofs can last about 40 years—double the life expectancy of a traditional roof. Ecoroofs also improve insulation, which provides savings in the form of lower heating and cooling costs.
Work with a design professional to obtain required permits.
Ecoroofs need regular maintenance. Ordinary maintenance tasks include:
- Occasional summer watering.
- Occasional weeding, especially in the first two years while plants are becoming established.
- Occasional cutting of plants and removal of dry materials, especially in the summer.
- Regular inspection to ensure proper drainage.
Stormwater Management Manual
Consult the City’s Stormwater Management Manual for the complete set of requirements on how to design, build, and maintain ecoroofs or other stormwater management solutions on your property.
Portland's Clean River Rewards Program
Residential and commercial property owners who install qualified stormwater management solutions may be eligible for discounts on the stormwater charges of their sewer, stormwater, and water bill through Clean River Rewards
Ecoroofs that meet the safety and space requirements in the stormwater manual are eligible for Clean River Rewards. If the ecoroof only partially covers the roof, it may be eligible for a partial discount. Visit Clean River Rewards to learn more.
Please note that roof gardens planted for food production are ineligible for the discount.
Find More Resources
Suggested plants can be found in the Ecoroof Plant List at the end of the Stormwater Management Manual. For more plants to consider, consult the Portland Plant List.