Sidewalks vs Trees: Smarter Solutions

By Susan Mates

Photo: Bart Everson

Urban foresters and engineers are increasingly using creative designs and materials

that allow trees to thrive while sidewalks remain intact. Often, prevention is

cheaper than repair, so better planning and design can prevent these conflicts in the

first place. That can mean:

● Provide larger planting areas or connected soil spaces to allow roots to

spread underground instead of pushing upward.

● Create deep, well-structured soils to encourage roots to grow downward

rather than remaining at the surface.

● Use better sidewalk construction techniques such as thicker pavement,

adequate base materials, and flexible design options.

● Select trees that fit the available space.

● Manage roots with root pruning, barriers, and irrigation strategies that

influence their growth patterns.

Here are some solutions that help trees live and grow, even when they are near

sidewalks.

Offset Sidewalks

One of the simplest solutions is simply changing the path of the sidewalk.

Instead of cutting roots, planners can reroute the walkway slightly around a mature

tree. These offset sidewalks create more space for roots to expand while

maintaining a safe walking path. They can also be used proactively when planting

new trees, ensuring adequate growing space from the beginning. In some cases, the

sidewalk may curve gently around a trunk, turning a problem area into a design

feature.

Alternative Paving Materials

Traditional concrete is rigid. When roots grow beneath it, cracks and lifting often

follow.

Photo by Edward F. Gilman, Professor, Environmental Horticulture Department, IFAS, University of Florida

Alternative materials offer more flexibility:

● Pervious concrete or permeable pavement, which allows water and air to

pass through. That encourages roots to grow deeper rather than pushing

upward.

● Brick or modular pavers that can be lifted and reset during repairs.

Because pavers are installed in individual units instead of as large slabs, they

are easier to repair and less likely to crack when roots expand beneath them.

● Rubber or composite pavers that flex slightly with root growth. Rubber

sidewalks are made of recycled tires and come in pre-manufactured panels.

Installation is more expensive, but there are some long-term advantages.

Water can penetrate rubber sidewalks, which means roots stay smaller, since

they don’t have to travel under a sidewalk to find moisture as they do under

concrete. Plus, concrete often fails quickly around large trees or expansive

soils, requiring concrete to be torn out and replaced. Rubber sidewalks can

be easily maintained and last about 20 years—and they are more

comfortable for walking or running.

Structural Soil

Sometimes the best solution lies beneath the sidewalk.

Photo by Jonathan Borb

Structural soil is an engineered soil mixture that is generally comprised of 80%

crushed rock and 20% loam soil. It provides enough stability to support pavement

while still leaving spaces for air, water, and root growth. This allows roots to grow

deeper under sidewalks instead of crowding near the surface.

Structural soil can be installed under new sidewalks or during major repairs,

helping trees develop healthier root systems and reducing future conflicts. It’s a

relatively inexpensive solution. However, its low soil volume limits its ability to

support large, healthy urban trees.

Silva Cells and Underground Soil Systems

Some cities are going even further with advanced underground systems.

Silva Cells and similar products create an underground framework that supports

sidewalks or plazas while leaving large volumes of uncompacted soil available for

roots. Modular, plastic cells hold up the pavement above, while soil fills the space

below, preventing the soil from being crushed and compacted.

Photo: Silva Cells, SDOT Photos

This approach is often used in new developments or street redesigns and can

dramatically expand the underground growing space for trees, without sacrificing

pedestrian infrastructure and providing a longer life for trees.

Root Barriers

Another tool is the root barrier, which directs roots away from sidewalks.

Photo by Edward F. Gilman, Professor, Environmental Horticulture Department, IFAS, University of Florida

These barriers—made from durable plastic or specialized materials—are installed

vertically in the soil between the tree and infrastructure. When roots encounter the

barrier, they are deflected downward to grow beneath the pavement rather than

pushing against it as they seek water and nutrients.

Because use of root barriers reduces the risk of damage to infrastructure and does

not need frequent maintenance, urban arborists may be included to use them for

trees in urban spaces. There are some considerations, though. When root barriers

restrict root growth, trees may suffer from nutrient deficiencies and water stress. If

trees are forced to grow deeper instead of wider, they may be more prone to

drought or be less stable.

Root barriers are often used when new trees are planted near sidewalks or curbs.

They may be a more suitable solution for certain tree species or locations.

Innovative street planning design

Projects such as curb extensions and expanded planting strips create more soil

space for trees while improving pedestrian safety.

Photo: Portland Bureau of Transportation

In places where there isn’t sufficient space for trees in the right-of-way behind the

curb, room for trees can be constructed by carving out space from the parking

zone.

You can see the results of some pilot projects for this in Portland on SE Duke

Street from 82nd to 94th Avenues and 89th and 90th Avenue, where Urban

Forestry contractors planted trees in January 2025, or near Lents Park where trees

were planted in February 2026.

In Seattle, engineers working on sidewalk repairs along Beacon Avenue explored

several creative ways to preserve mature street trees. Strategies included narrowing

sections of sidewalk widths or creating "cut-outs" to create more space for tree

roots, raising the sidewalk grade to accommodate roots, and using alternative

materials like aluminum plates in specific locations to reduce root damage. The

goal was to keep as many trees as possible while still maintaining accessible

sidewalks.

Looking Beneath the Canopy

Urban trees deliver some of their greatest benefits later in life, when they are tall

enough to shade streets, cool neighborhoods, and absorb stormwater. Losing a

mature tree because of sidewalk damage means losing decades of ecological and

community value.

With thoughtful planning, urban planners and arborists are discovering that healthy

sidewalks and healthy trees don’t have to compete for space. In fact, when we

design for both, our streets become safer, greener, and more resilient for everyone.

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Resources:

● Trees in the Curb Zone Pilot Project, Portland Bureau of Transportation –

● Trees and Sidewalks - Healthy Roots, Healthy Tree, Carrie Black, Portland

Urban Forestry, March 30, 2021.

● Trees and Sidewalks: A Strategic Approach to Conflicts, Leda Marritz,

DeepRoot Blog, July 17, 2017.

● Reducing Tree Root and Sidewalk Conflicts: Analysis and Strategies for the

City of Palo Alto, Elise Willis, City of Palo Alto, October 5, 2016.

● The Limitations of Structural Soil: Why It’s Not the Best Solution for

Expanding Total Soil Volume, Jacob Westlin, Deep Root Blog, August 25,

2023

● Trees and Sidewalks Operations Plan, Seattle Department of Transportation,

February 2015.

● South End Life: How Trees Stand Up to Sidewalk Repairs on Beacon

Avenue, Yuko Kodama, South Seattle Emerald, August 16, 2025.

● New Rubber Sidewalks Tested in 60 Cities, Nei Greenfieldboyce, WUNC

News, August 4, 2006.

● Rubber Sidewalks Save Trees and Money, Carl Brahe, Commercial Real

Estate Inspections and ADA Surveys, 2026.

● Silva Cells, Brightside, St. Louis

● How Root Barriers Came to Be, Leda Marritz, DeepRoot Blog, June 10,

2011.

● The Debate on Root Barriers: Friend or Foe to Trees? Lee Sprinkler

Drainage.