Daniel Burnstein of Brooklyn, New York had a unique dilemma: his client wanted to be able to use the backyard with a wheelchair. Concrete work and pavers can be expensive, and Daniel liked the rustic charm of gravel.
His question: Can gravel surfaces be wheelchair accessible? The answer is yes—if they meet certain standards.
Washington Rock, with the help of landscape architect Clayton Beaudoin, researched the topic and came up with guidelines for making gravel surfaces wheelchair accessible.
Our goal is to make these guidelines as easy as possible to follow, so we create a simple guide below. Then we included additional resources, such as a Glossary of Terms and Research Notes.
Stay tuned for the companion piece to this article about how we helped Daniel and his client create a gravel-accessible backyard.
What Exactly is an “Accessible” Surface?
According to the ADA, an “accessible” surface is firm, stable, and slip-resistant. Check out our Research Notes for more information about ADA standards. In the next section, we’re going to share the guidelines shaped by these standards.
8 Guidelines for Creating an Accessible Gravel Surface
We created 8 guidelines for creating a wheelchair-accessible gravel surface, using regulatory standards and a construction model. Our models are adapted from a crushed surfacing model shared with us by Clayton. Below is a graphic with all of the steps. The steps are described in greater detail below the graphic.
Guideline #1: Choose a Preparation Method
If you expect heavy foot traffic or the ground is soft or muddy, use the Standard Method.
If expect light foot traffic or the ground is firm, use the Light Method.
Guideline #2: Prepare the Subgrade
Standard Method: Excavate your project area to 6 inches deep. Then compact, preferably with a plate compactor. The end result should be a smooth and level surface to place gravel on. Since you will need to taper the edges of the gravel area, make sure to take this into account in your design. See Guideline #6 for more info.
Light Method: Excavate your project area to 3 inches deep. Then compact, preferably with a plate compactor. The end result should be a smooth and level surface to place gravel on. Since you will need to taper the edges of the gravel area, make sure to take this into account in your design. See Guideline #6 for more info.
Guideline #3: Purchase the Right Kind and Quantity of Gravel
Light Method: Your project will need 3 inches of ¼” minus rock only.
¼” minus is basically a coarse crusher dust that becomes cement-like after compaction. The key is to find minus gravel in the smallest size possible. Our ¼” minus Trail Mix gravel is an excellent option. Decomposed granite is a good substitute. In a pinch, you could use a slightly larger minus rock product, but you run the risk of having larger pieces of rock getting kicked around and impeding accessibility.
5/8” minus in Washington State is also known as Crushed Surfacing Top Course and is a DOT-spec product typically used to build roads. If this size is not available in your area, driveway gravel ranging between ½” and ¾” minus will do. You might find similar products under other names, depending on the region of the U.S. you live in: Item #4, Crusher Run, Quarry Process (QP), Dense Graded Aggregate (DGA), and Shoulder Stone.
Be sure to use quarried or 100% fractured gravel products, not crushed round rock products. Quarried and fractured crushed rock products will compact better because they have angular edges while crushed round rock will have some rounded edges.
To determine how many cubic yards of gravel you need to order, check out our handy guide. When ordering materials, it’s a good idea to order extra gravel. In construction, most contractors factor in 10–20% more materials as a contingency.
Guideline #4: Add Gravel to the Excavated Site
Standard Method: Place 4 inches of 5/8” minus throughout the excavated area. Then place 2 inches of ¼” minus on top of the 5/8″ minus layer.
Light Method: Place 3 inches of ¼” minus throughout the excavated area.
Guideline #5: Slope the Surface of the Gravel Area
For both methods: Place slightly more material in the middle of your project area, then place less and less material as you reach the edge of the excavated area. You want to slope the surface of the gravel just enough that water will drain off the sides of the gravel area. Otherwise water may pool on the surface because the compacted gravel will function similarly to paving.
Check out the Research Notes section for more information about ADA slope requirements.
Guideline #6: Angle the Edges of the Gravel Area and Backfill Around the Edges
For both methods: The edges of the gravel area should taper at a 45-degree angle from the base of the gravel layer to the top. This will help water drain away from the gravel area.
Since there will be a gap between the top of your gravel layer and the subgrade, you will need to backfill this gap with soil.
Guideline #7: Compact the Gravel (and the Soil Around the Edge of the Gravel Area)
For both methods: Gently water the gravel with a hose using the “shower” or “garden” setting on your hose attachment, if you have one. (Water will drive the fines on the surface down into voids in the gravel layer, leading to better compaction.)
Use a plate compactor to compact the gravel until the surface is firm and doesn’t indent when you walk on it. Be sure to also compact along the edges where you backfilled. With the Standard Method, you may choose to compact each layer separately.
Guideline #8: Maintain the Gravel Area
For both methods: Compacted gravel surfaces “require maintenance to maintain smoothness and sometimes slope,” Clayton explained. Maintenance may include fixing divots or potholes, regrading the surface to evenly redistribute material, or adding and compacting more gravel on the surface to keep it level with adjacent surfaces.
Weed growth can also occur, especially around the edges of the gravel area, unless the area is treated with a solution like weed killer.
Other Project Materials to Consider
Edging: Any edging will do, depending on how important it is for the path definition to remain neat and tidy.
Landscape Fabric: When it comes to landscape fabric, Clayton explained that Site Workshop doesn’t typically use landscape fabric underneath gravel “unless the subgrade is weird.”
Gravel Binders: Resin-based gravel binders like Gravel-Lok or Gravel Glue are sometimes used to keep gravel from moving around and can also stunt weed growth. Clayton explained that rain, UV light (sunshine), and foot traffic will eventually wear the binders out, and the binders will have to be reapplied. Whether or not you use binders depends on whether you think it’s worth the cost and labor of reapplying.
Other Accessibility Factors to Consider
In addition to choosing the right gravel and constructing the surface correctly, you might also want to consider other factors in the design of your gravel surface. Click on the links within each bullet point to view accessibility standards that can guide the creation of your gravel project.
- Do wheelchairs have enough room to turn?
- Are paths wide enough for wheelchairs?
- Is there enough space for wheelchairs to pass by each other?
- Are slopes gradual and not too steep?
Glossary of Terms
- Accessible Surface: According to the ADA, accessible surfaces must be firm, stable, and slip-resistant.
- Angular vs. Subangular vs. Round: angular means the edges are sharp while subangular means that the edges are blunted. Angular products will pack down more because the pieces fit together like a puzzle. Rounded products will not pack as well and will roll more. So subangular is a compromise between these two extremes.
- “Clean” v. “Minus” Rock: Clean rock products contain no fines (small particles of ground rock). Minus rock does contain fines. Fines help a product compact. For a more in-depth explanation, check out our “Clean v. Minus” article.
- Compaction: the process of exerting pressure on gravel to make it more dense (i.e., more firm and stable). Gravel is often compacted by being pressed on with a plate compactor or tamper. Water is sometimes used as well to help fines work their way into the gravel.
- Fines: very small particles of rock. Fines help materials compact but can also make materials dusty or dirty.
- Gradation v. Size: gradation refers to the size variations that make up a single rock product. For example, a crushed rock product will have a certain percentage of the product that passes through screen size A, a certain percentage of the product that passes through screen B, etc. That’s why some rock products contain rocks of relatively the same size and no fines while other rock products contain rock pieces of many different sizes. Because of how gradation works, ¼” minus is actually made up of pieces of rock that fit through a ¼” sieve diagonally, some of which are slightly larger than ¼”. It also includes a certain percentage of material that passes through smaller sieve sizes. So it’s more accurate to refer to ¼” minus as the product’s gradation rather than the product’s maximum size.
- Subgrade: ground that is prepared to act as a foundation for other materials, e.g., the compacted ground the gravel is placed on
Below you’ll find a compilation of information about accessibility standards and gravel accessibility.
A Brief Introduction to ADA Standards, ABA Standards, and the U.S. Access Board
Private homeowners generally don’t need to worry about meeting accessibility standards beyond what residential construction laws require. But accessibility standards provide good minimum guidelines for those looking to enhance the accessibility of their yards. Below is some background information about ADA and ABA standards as well as the U.S. Access Board, which are referred to in this article.
ADA stands for the American with Disabilities Act, signed into law in 1990. According to the ADA government website, the purpose of the ADA is to guarantee that people with disabilities “have the same opportunities as everyone else to participate in the mainstream of American life.” Included in the legislation are standards for accessible design that public and commercial buildings must meet. These accessibility standards apply to “places of public accommodation, commercial facilities, and state and local government facilities in new construction, alternations, and additions. The ADA Standards are based on minimum guidelines set by the Access Board” (U.S. Access Board website).
The ABA stands for the Architectural Barriers Act, signed into law in 1968. ABA Standards were the first of their kind in the U.S. to establish accessibility standards for “facilities designed, built, altered, or leased with federal funds,” including national parks (the U.S. Access Board website). ABA Standards are established by the Department of Defense, the Department of Housing and Urban Development, the General Services Administration, and the United States Postal Service based on guidelines issued by the U.S. Access Board.
The U.S. Access Board is an independent federal agency that provides guidance and training on all accessibility standards, including the ABA and the ADA. It also investigates complaints and conducts research on accessibility issues. The Access Board website is a great resource that includes the full text of many accessibility laws and policies, including the ADA and the ABA.
What Do Accessibility Standards Say About Gravel?
ADA Standards on floors and ground surfaces require that surfaces are stable, firm, and slip resistant. (To understand exactly how the ADA defines “stable,” “firm,” and “slip resistant,” see Section 302).
The ABA guidance on trails goes on to explain that firm and stable trail surfaces must resist “deformation by indentations. A stable trail surface is not permanently affected by expected weather conditions and can sustain normal wear and tear from the expected uses between planned maintenances.”
In the Guide to ADA Accessibility Standards, Chapter 3: Floor and Ground Surfaces, the article states that “most loose materials, including gravel, will not meet these requirements unless properly treated to provide sufficient surface integrity and resilience. Binders, consolidants, compaction, and grid forms may enable some of these materials to perform satisfactorily but require repeated maintenance.”
Clayton stated that the proper gravel gradation and compaction are key to making gravel surfaces accessible.
Federal guidelines for outdoor areas are not quite as rigid. The Guide to the ABA Accessibility Standards guide states that while paving is appropriate for highly developed areas, “for less developed areas, crushed stone, fine crusher rejects, packed soil, soil stabilizers, and other natural materials may provide a firm and stable surface” (“Chapter 10: Outdoor Developed Areas” under trail building).
The U.S. Access Board offers a list of stable materials, including the following:
- crushed rock
- rock with broken faces
- a rock mixture containing a full spectrum of sieve sizes (a.k.a. gradation)
- hard rock
- rock that passes through a ½” screen
- rock material that is compacted in 3- to 4-inch layers
- material that is moist before it’s compacted
- material that is compacted with a vibrating plate compactor, roller, or by hand tamping
According to Clayton, “Properly compacted and maintained crushed rock surfaces (¼” minus over 5/8” minus or thereabouts) are considered accessible surfaces” in the State of Washington by institutions like school districts and parks departments, who are particularly sensitive to ADA rules.
Clayton mentioned that he has included these exact types of pathways on many public projects.
ADA and ABA Resources
- Measuring Surface Firmness and Stability
- Guide to the ABA: Chapter 3: Firmness, Stability, and Slip Resistance
- Guide to the ABA: Chapter 10: Outdoor Developed Areas
- 2010 ADA Standards for Accessible Design
Check out our ¼” minus Product Page for more information. You can also read our article about how a horse farm uses compacted ¼” minus for events and then turns it over in the winter for their horse arena.
For more information about landscape architecture firm Site Workshop, check out their website.