In this group project for RISD’s Fall 2022 course “Material Assemblies,” we explore incorporating sustainable materials into an urban tree pit design along South Water Street in Providence, RI.

A Smarter Tree Pit

Instead of confining a tree’s root in a concrete box, our tree pit design incorporates an underground “soil tunnel” to an adjacent grassy parcel under the existing sidewalk. The soil surface around the tree’s trunk is sunk below the surface of the sidewalk, topped with a mycelial seed mat, and protected from trampling by a grate. The tree is flanked by two benches made of red-oak “slices” skewed onto a galvanized steel rod. The bench design promotes the growth of flowering fungal bodies, such as turkey tail (Trametes versicolor), and allows for modular replacement of decayed slices. The tree pit is surrounded by 5x5x5 inch black locust pavers, embedded in a wire-mesh grid from below. In high-traffic areas, the matrix is filled with rice gravel, promoting water infiltration and lessening eventual street runoff. In lower-traffic areas, such as by the benches, the matrix is filled with a baked mycelium spacer module. 

Left + center: 3D model (by ZT) and physical model (by AM) cross-sectional views of our tree pit.

Right: Mycelium spacers (light brown) sandwiched between black locust pavers (dark brown).

Why Mycelium?

Upstate New York-based company Ecovative sells Grow It Yourself® kits (bags of hemp hurd and a proprietary blend of mycelial spores) that allow anyone to create a sustainable construction material at home. Once exposed to the elements, the rigid mycelial material becomes home for species such as lichens and mosses and can decompose to enrich underlying soil and root systems.

Molding the Mycelium 

To create the mycelium spacer prototype, I made and translated a 3D Rhino model into a laser-cut template. As an experimental variable, the cutting template contained pieces to create both full- and half-height spacer molds. Eighth-inch acrylic was cut, assembled, and filled with inoculated substrate. After a few days, the “cemented” spacers were removed from their molds and baked to terminate the mycelium growing process.

From left to right: Rhino 3D mockup and laser-cut stencils, laser-cut acrylic mold once assembled, mycelium spaces after baking.

AutoCAD Documentation

Project partners:

• Aleece Mount (RISD MLA ‘23)

• Zhehao Tang (RISD MLA ‘23)