Flagstone treads could be used as treads on segmental retaining wall risers.  Steps are constructed on a 6-inch base of compacted crushed stone, and at least 8-inches of wall stones below grade, but they do not require a concrete foundation so they are more economical than masonry  steps.  Flagstone treads are installed with Segmental retaining wall adhesive.
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Please view some examples of our flagstone & SRW steps below.
All steps shown were constructed by Robert J. Kleinberg Landscape Design and Construction.  He is an ICPI Certified Concrete Paver Installer and a NCMA Certified Segmental Retaining Wall Installer.  He is also an EP Henry Authorized Hardscaping Contractor, and has been designing and constructing patios, steps and gardens in Philadelphia, Montgomery County ( Lower Merion, Bala Cynwyd, Ardmore, Narberth ), Delaware County ( Havertown, Marple, Drexel Hill, Lansdowne, Springfield, Swarthmore, Ridley, Media, Upper Darby, Newtown Square, Radnor ), and the Main Line ( Bryn Mawr, Villanova, Gladyne, Wynnewood ) PA as a Landscape and Hardscaping contractor since 1986.

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NCMA Certified Segmental Retaining Wall Installer

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Terrace Wall step and landing during construction:

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