Natural resources and environmental overlay zones

A black and white map showing differently marked zones
The difference between conservation and protection overlays and how the overlays impact properties.
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The following is a general explanation of the environmental overlay zones but does not cover all situations and circumstances. It is important to refer to the actual environmental zone code, Chapter 33.430 to understand how the regulations apply to any given site. 

What are environmental overlay zones?

Environmental overlay zones, or ezones, and the regulations that accompany them, are a tool used by the City to help protect important natural resources in Portland. Examples of natural resources identified by the City for protection include:

A stream, with houses on both sides, surrounded by trees.
  • Rivers, streams, drainageways, and wetlands – this is where fish and wildlife live; these features move water from land to larger rivers and the ocean; they also cool the air and provide places for people to recreate
  • Floodplains – this is where the water goes when it floods; development, like houses, businesses and parking areas, can be damaged during floods; filling in the floodplain can make flooding worse elsewhere
  • Forests and woodlands – this is where wildlife live and people go to hike, bird watch, and relax; trees cool the air and improve air quality, and trees help hold steep slopes in place
  • Unique habitats – large meadows, oak groves, bluffs and other unique features in the city provide habitat and respite for wildlife

Typically, ezones apply to the portions of a site that contain natural resources or areas, that if disturbed, would have a negative effect on those natural resources or the surrounding property.

What does it mean to have ezones on my property?

You can find out if there are ezones on your property by looking up your site address in the Ezone Review Map.

Ideally, the portion of your property that is in an ezone should be left natural and undeveloped. However, many of the natural resources in Portland have been altered by yards, driveways, parking areas, docks, and even portions of houses and buildings. These areas still provide functions, like flood storage, and additional impacts should be avoided.

When new development, like an addition to your house or a new parking area, is proposed in an ezone, impacts to the resources need to be minimized as much as possible and any resources negatively impacted or destroyed must be replaced. To ensure the proposed development meets zoning code requirements,an Environmental Review by the Bureau of Development Services may be required. 

What’s the difference between conservation and protection overlay zones?

A black and white map showing differently marked zones

Outside of the Willamette River area, there are two kinds of environmental overlay zones: Environmental Conservation (c-zone) and Environmental Protection (p-zone)

The c-zone is applied to natural resources that are important but where some environmentally sensitive development may be permitted. The p-zone is applied where the resources are critical and development should be avoided except under special circumstances, such as when a public road needs to cross a stream or drainageway. In either c- or p-zones, the location and extent of development needs to minimize impacts on the resources, and the property owner is responsible for the replacement of any resources that are lost. 

What is Environmental Review? 

Some development and activities are exempt from the ezone code, which means the ezone regulations don’t apply. An example of an exemption is development over an already paved surface in an ezone; as long as that development is more than 50 feet from a stream, drainageway, wetland or other water body. 

If the development or activity is not exempt, it will need to be reviewed against the development standards. Standards reflect situations where minimal impact to the resources are allowed under certain circumstances. When the activity or development can meet standards then only an Environmental Plan Check by the Bureau of Development Services is required. For example, standards for stormwater outfalls specify how large a pipe can be used, how much area can be disturbed to install the pipe, what plants and trees can be removed, and other aspects of the construction work and impact area.

If the proposed activity or development isn’t exempt and cannot meet the standards, then an Environmental Review is required. During Environmental Review an applicant needs to show how the proposal avoids and minimizes impacts to the natural resources and, if the impacts can’t be avoided, how impacted or destroyed resources will be mitigated. 

More about Environmental Review.

Does the ezone mean I can’t plant a garden in my yard?

A permitted lawn or landscaped area in the c- or p-zone can be converted to a garden if no trees are removed. Existing gardens, lawns, and other landscaped areas in c- or p-zones can be maintained and new plants can be installed if they are not listed as a nuisance species on the Portland Plant List.

An illustrated drawing, showing a house surrounded with trees, next to a stream

In a portion of the c- or p-zone that is not already landscaped, a new garden can be added if the garden is less than 500 square feet in size, no trees are removed, it is no closer than 50 feet to a stream or wetland, and cumulatively the site doesn’t exceed the maximum disturbance area limitations for the base zone. However, if the garden can be placed within an existing lawn or completely outside the environmental overlay zones, that is the preferred alternative. Please see zoning code 33.430.080.D.9.

Does this mean I can’t repave my parking area?

You can maintain, repair or in most cases replace parking areas and other existing structures, like buildings, in the c- or p-zone if the footprint of the parking area or building doesn’t increase. Please see 33.430.080.C.

An illustrated drawing showing a large warehouse with trucks docked outside. The building is next to a stream and surrounded with trees

Does this mean I can’t add a deck to my house or expand my parking area?

Expanding the footprint of development in the ezones – making it bigger – is more complicated. It depends on how much of your property is in the ezone and how much of the site has already been developed or disturbed. Please see 33.430.140.A-S.

What if there is a drainage on my property that is not in an ezone?

A drainageway under trees

All drainages that move water from upland areas to pipes, streams, wetlands or rivers are regulated by the City. 

Rivers, streams, and wetlands that provide a variety of functions such as fish and wildlife habitat, stream flow, pollutant and sediment filtering, food web, nutrient cycling, microclimate, etc. are typically regulated by the e-zone. Those waterways may be dry for part of the year or may flow through a pipe or culvert for some distance.

There are smaller drainages that move water only after a rain event and don’t provide the same level of functions as rivers, streams or wetland. These drainages are important for directing stormwater to pipes or streams and reducing damage to property. These drainages may not be within an ezone. Instead, the drainage may be regulated by Chapter 17.38, Drainage and Water Quality.

What if there is floodplain on my property that is not in an ezone?

A large flooding body of water digging up the ground next to a house

The floodplain is an area that has a risk of flooding. All parts of the 100-year floodplain are regulated to reduce risk for property and structures.

Those regulations are found in Chapter 17.24. The portion of the 100-year floodplain that is vegetated or near a river, stream, or wetland may also be regulated by the e-zone.

What if, after this project is over, the ezone is still not correct on my property?

Staff is working hard to update ezones through the E-zone Map Correction Project; the goal of the project is to produce accurate and consistent mapping throughout the city. Staff can perform a site visit to verify the location of the streams, wetlands and vegetation on your property. To request a site visit please call 503-823-4225 or email

However, the ezone boundaries will never be 100% perfect because:

  • Nature changes – streams shift course, wetlands grow or shrink, trees grow or die
  • New technology or survey techniques improve the accuracy of mapping
  • Staff won’t be able to visit every single site during this project

There is a free process that property owners can use to request that the City correct the ezone boundaries. Property owners can request a correction at any time. Zoning code 33.855.070 provides the details. 

If you have additional questions or comments, please contact project staff:

Phone: 503-823-4225