Sidewalk Greening
by Mei Ling Hui
In 2006 a new permit called the Permeable Sidewalk Landscaping Permit was passed which allows the creation of gardens in the sidewalk by the removal of strips of concrete along the curb. These gardens have the potential to provide numerous ecological and economic benefits to our urban environment. Studies have shown that plants and landscaped areas can make us safer, happier, and wealthier.
These gardens can reduce the speeds of traffic and create a physical and mental barrier between the street and the sidewalk, keeping pedestrians, children and pets out of harm's way. They can reduce crime by creating a street that looks more cared for and by encouraging people who live near them to spend more time outside and around their homes which can increase neighborhood involvement and awareness of what type of activities take place on your street. Plants also increase the amount of time a shopper is willing to stay in a commercial district and increase the amount of money they spend while they are there by up to 12%. Landscaping can also significantly increase the value of a property and in some cases this permit may be the only way a building owner can landscape their property in this city.
The replacement of concrete by plants allows for the absorption heat instead of reflection of it. This absorption of solar energy reduces the Urban Heat Island effect, a phenomenon which can significantly alter surrounding ecosystems and increase the amount of energy used in the city. These open areas also absorb more rainfall, reducing the strain on our combined sewer system, a system that mixes building waste with street water runoff before processing. In periods of high rain fall our sewer system can't handle the volume of water that passes through it and the combined sewage is released directly into the bay without being cleaned. Removing a 3' square of concrete will reduce the amount of rainfall run-off by five gallons for every inch of rain that falls.
And perhaps most interestingly to us here at FUF, these gardens reduce the amount of concrete around a tree which reduces how much the trees and sidewalk affect each other, resulting in healthier trees and less concrete that needs to be maintained. And while these garden spaces have the same requirements of passable space for pedestrian traffic as trees do, they can be installed in areas where trees can't be planted due to proximity of existing utility lines, street corners, or other infrastructure.
Creating Permeable Sidewalks with Neighbors
So-called permeable sidewalks bring more greenery to our streets, thus enhancing property values, providing pollution abatement, helping stormwater runoff, and in general improving our quality of life. While you are certainly free to initiate a permeable sidewalk on your own, we recommend coordinating your efforts with neighbors. The permit is less expensive when more addresses apply together, and economies of scale in ordering materials and services allow further savings. (Permit fees are $215 for one home, $185 for two to four, and $160 for five or more.) Installation is also much easier and enjoyable when many hands are working together.
Before you and your neighbors start planning, review the permit guidelines on the city website. These projects can be complicated and each site will be different depending on the existing conditions.
The application has two parts: a form and a site drawing, which is an overhead view of the proposed garden area. After submitting the forms, the Bureau of Urban Forestry (BUF) will conduct a site review, over your plans and potentially asking for corrections or changes.
Some things to keep in mind while designing your site:
Gardens must leave passable space at least 4’ wide in the remaining sidewalk.
In order to insure safe passage around and through these gardens, a 2-foot wide strip must be left on the curb edge. There will need to be periodic 4-foot wide paths from the street to the remaining sidewalk. These strips can be left as concrete, or the concrete can be removed and pathways created with materials such as pavers, brick, or decomposed granite; pathways must be level and provide firm support.
The sides of planting areas, perpendicular to the sidewalk, must have a raised edge between six and 15-inches tall to alert vision impaired individuals to a change in the available path of travel.
Sidewalk fixtures such as street signs must be left where they are and anchored securely in place. Utility boxes must also be left uncovered and must retain a six- inch plant-free perimeter to maintain access.
Though these gardens can be safely installed directly over existing utility lines, it's important to have the utility companies come and mark where their lines are underground. The homeowner is responsible for making sure these lines are not disturbed.
After BUF approves the plans, installation can begin. There are resources for concrete removal on FUF’s website, but you can also rent equipment and remove the concrete yourself. In many cases, taking out sections of sidewalk can be the most expensive part of the project. Plan on planting the garden as soon after removing the concrete as possible. Secure the opened sidewalk area with barricades, bollards or caution tape until the project is complete.
Sidewalk cement is typically two to four-inches thick, and in replacing it, the new garden will need quite a bit of new soil. The existing soil will need to be disturbed before mixing in the new soil, as it was heavily compacted before the sidewalk was poured. If the soil is not loosened, water may not percolate beyond the added soil and it will be difficult for any plants to survive.
Before installing plants, lay out the pathways according to your plans. Pathways created from loose materials like decomposed granite need to be retained with bender board and tamped to avoid wearing away. Hilly or steep locations may require terracing to prevent erosion.
New plants should be kept at least three-feet from the base of existing trees to help prevent competition of resources and root crown rot. They must also not grow so tall as to obstruct site lines. The best plants are drought tolerant, but it's also important to consider how delicate the plants are and how long they take to establish. The plants in these gardens are probably going to be stepped on from time to time.
After the gardens are complete, BUF will visit again and either approve the work or ask for changes. If work deviates from the approved plans, BUF may require the site to be fixed, which can be costly and time consuming. Remember you will have to maintain these sites, watering and weeding them, and keeping them clear of trash.
The cost of your project will be largely determined by what materials you use and where you get them. Concrete removal averages between 5 and 10 dollars a square foot to remove, or roughly $50 to $100 to remove the typical 3 x 3-foot sidewalk flag. Pathway materials range widely, based on how much area you are required to maintain as path and what you choose to create it from, anywhere from less than two dollars to more than $10 per square foot. The same holds true for plant materials. Other materials are determined by the project plan and can include rebar, nails, redwood stakes and boards, fences, sand, mulch, and weed-cloth. Some necessary tools could include shovels, picks, rakes, trowels, hammers, saws, brooms, soil tampers, wheelbarrows and gloves.
Friends of the Urban Forest is starting a program using the Permeable Sidewalk Landscaping Permit, which we are calling our Basin Expansion Program. We are targeting addresses with existing trees to improve the health of the tree among many other benefits. The Basin Expansion Program is much like our Neighborhood Tree Planting Program in that they are community driven events that FUF facilitates. A neighborhood volunteer will organize their street and when between 10 and 15 addresses sign up for the project, we will schedule a planting date.
When FUF sponsors a neighborhood planting, we will perform all necessary site reviews, create the site plans and drawings after consulting with the homeowner, file all necessary paperwork and act as a liaison between the city and the homeowner, arrange for the removal of concrete, determine what the best available materials are and have the correct quantities delivered to the site, provide volunteer support and tools for planting day, and cover part of the project’s costs.
For more information about how to start a neighborhood planting, contact our community outreach coordinator Greg Harrell-Edge at greg@fuf.net or 415.561.6890 x 101.
