Completed in 2018, our cob structure steals the show for most of the year. Flowers get the attention late summer to fall, but the rest of the year, the deliciously earthy walls of our cob house capture your eyes. The structure was built to function as a playhouse, shade structure and a meeting place for our young visitors. Huge thanks to Pete Poli for his guidance and teaching of the natural building process!
The base of the walls are made from repurposed concrete pieces mortared together to provide protection from rain to the lower sections of the wall. The large overhand of the green roof provide water protection to the upper portions of the wall. The inner wall is made from a material called Cob. It’s an ancient building technique used all over the world where clay and sand are readily found. Our mixture also included straw, which acts as rebar to prevent the walls from cracking. Unlike adobe, which is made from formed bricks stacked together, our cob walls are monolithic–the walls are formed as a single integrated form held together by the fibrous material.
Cob is traditionally formed by the work of feet, integrating the clay and the sand. Over 200 volunteers of all ages participated in this activity, with the walls being fully formed in late Aug-early October 2016.
After allowing the walls to dry and harden until the following summer, we were ready to add a lime 
plaster layer for weather protection and color in August 2017. The exterior layer is a mix of hydrated lime, fine sand, and cattail fluff for the fiber. We added mineral pigments using a fresco painting technique to the lime plaster to give the structure its tan color. An Oak tree was formed on the outside of the building, honoring the species’ vital role in our ecosystem–it’s strong, beautiful, but most importantly, host to over 600 species of insects! The shape of our tree was drawn by local artist Susan Peterson and formed using a cob mixture and topped with lime plaster and pigment.
Early summer 2017 also saw the addition of our green roof, thanks to Eagle Scout Jack Frane. The base plywood layer is topped with a pond liner to prevent water from contacting the plywood. Next a drainage membrane was added to allow channels for water to drain. This was topped with a landscape fabric keep sediment from filling drainage membrane. Lastly, we added a special green roof soil substrate made from expanded clay that allows superior drainage. Thanks to Midwest Trading for their donation! Lastly, I selected native plants that have evaluated by Chicago Botanic Gardens Green Roof trial to show resiliency for the tough growing conditions on a green roof. Plants like: nodding onion, prairie smoke, prairie clover, prairie dropseed, side oats grams, hairy penstemon. Interspersed between these plants are sedums, to aid as a groundcover to conserve moisture.
Our final addition to the cob house was summer 2018. Local artist Linda Doyle’s inspiration of native flowers frames the interior with color and lightness and beautifully complements our township’s support of native plants. Under the bench is a quote by Ralph Waldo Emerson, “The earth laughs in flowers”. Flowers certainly do make the world a lovelier place, and like laughter, it does a body good.
We invite you to stop by and feel the coolness of the walls, the texture, and feel the comfort of being surrounded by Mother Earth.
Check out our blogposts for more details on the building process and our green roof:
http://fremontgarden.org/natural-building-project-phase-1/
http://fremontgarden.org/natural-building-project-phase-2/
http://fremontgarden.org/natural-building-project-phase-3/