Part 1: The Basics
Dear Washington Rock: I’m creating a gravel garden path, but it has to pack well because a wheelchair will roll on it. I have to get this right so the homeowner using the wheelchair can get her exercise and use her garden.
Do you have advice on how to create a wheelchair-accessible gravel path?
—Daniel from Brooklyn, NY
Below you’ll find an in-depth discussion about how to make gravel surfaces wheelchair accessible. Check out Part 2: Application to see our video about Daniel’s project and how we adapted these standards using local materials. Part 2 has not yet been published.
The ADA requires accessible surfaces to be firm, stable, and slip-resistant. We found that gravel surfaces meet these requirements and can be made wheelchair accessible by meeting five conditions:
- the right gradation (size) of gravel is used,
- the subgrade (the ground the gravel will be placed on) is prepared correctly,
- the gravel is compacted,
- the surface is slightly sloped and the edges are angled to give water runoff somewhere to go,
- and the gravel surface is regularly maintained.
In the next section, we’ll share blueprints for meeting these five conditions. Then we’ll discuss in depth how to follow the model.
Blueprints for Preparing Wheelchair-Accessible Gravel Areas
We consulted with Clayton Beaudoin, who is a principal landscape architect for Site Workshop and has designed many public works projects, including Dune Peninsula at Point Defiance.
Clayton provided a blueprint that shows two different methods of preparing gravel surfaces. The Standard Assembly method is best for areas that get more foot traffic or are muddy while the Light Duty Assembly method is best for areas that get less foot traffic or have a firmer subgrade.
In the next sections, we’ll break down these methods using the 5 conditions we initially outlined.
1. Gravel Size and Gradation for Wheelchair Accessibility
In the blueprints, ¼” minus is king. The Light Duty Assembly method recommends 3 inches of ¼” minus. The ¼” minus product is basically a coarse version of crusher dust and becomes cement-like after being compacted.
Clayton explained that compacted ¼” minus “becomes like pavement (and is treated as such in most stormwater models) and can provide an unyielding surface capable of being accessible.”
Washington Rock produces a ¼” minus crushed basalt product that is used locally for park trails. It’s also referred to in our company as “Trail Mix gravel” because it’s so often used for trails. It creates a cement-like surface. In other parts of the U.S., ¼” minus might be sold as a coarse crusher dust. The key is that it contains a mixture of fines and larger pieces of rock that pass through a ¼” sieve. Decomposed granite is also a good substitute.
If you’re looking for a similar product in your area, look for a coarse crusher dust. Decomposed granite is a common product that will work as well.
If you have a muddy area or need more structure on top of your subgrade (ground surface), start with 4 inches of 5/8” minus rock followed by 2 inches of ¼” minus. Our 5/8” minus product is also known as Crushed Surfacing Top Course (CSTC) and is a gradation specified by the local Department of Transportation for paving projects.
Driveway gravel ranging between ½” and ¾” minus will do if 5/8” minus is not available in your area. 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.
Note that you will want to use a quarried or 100% fractured gravel product, not a crushed round rock. The quarried or fractured crushed rock products will compact better while crushed round rock will have some rounded edges. Also be sure to use a “minus” gravel that contains fines (rock dust). “Clean” or “clear” gravel will not have fines.
2. Preparing the Subgrade for Wheelchair Accessibility
The ground should be excavated from 3 to 6 inches deep, depending on which method you use. Then the ground should be firmly compacted, preferably with a plate compactor. The end result should be a smooth and level surface to place gravel on.
“Compaction is critical,” Clayton explained. “The subgrade below the two gravels must not yield.”
3. Placing and Compacting Layers of Gravel
Place each layer of gravel, one at a time, and firmly compact it using a plate compactor. If you use the Standard Assembly method, you’ll place and compact a total of 4 inches of 5/8” minus followed by 2 inches of ¼” minus.
If you use the Light Duty Assembly method, you’ll place a total of 3 inches of ¼” minus.
It’s a good idea to gently water the gravel with a hose before compacting and as you compact. Use the “shower” or “garden” setting on your hose attachment, if you have one. Water will drive the fines on the surface down into voids, leading to even better compaction.
4. Sloping the Surface and Angling the Edges
The gravel area should be sloped just enough that water runoff 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.
Clayton noted, however, that the slope must not be too steep. “Generally this means under 2% cross-slope (the slope from side to side) and under 5% in the running slope (the direction of travel),” he said.
The edges of the gravel area should taper at a 45-degree angle from the base of the gravel layer to the top.
5. Maintaining Wheelchair-Accessible Gravel Surfaces
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?
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.