Strawtegi CO2ttage Tiny House Competition Finalist Becomes a Reality AIA Utah partnered with Salt Lake City and the Community Development Corporation of Utah in 2021 to lead the Empowered Living Design Competition, a collaborative project to address housing availability and affordability. The competition generated dozens of design submissions from around the world for freestanding, compact dwellings referred to as either a tiny home (less than 400 square feet) or an accessory dwelling unit (ADU; less than 650 square feet). One finalist of the competition is now built and ready for occupancy in Salt Lake City. With a space-efficient design and a charming aesthetic character, the Strawtegi CO2ttage ADU supports sustainable urban lifestyles and is well suited to the vernacular of the local Sugar House neighborhood. More importantly, it was created by homeowner and designer Susan Klinker to demonstrate simple ways to achieve a Net Zero Carbon Footprint through a design that sequesters embodied carbon while accomplishing Net Zero operational carbon emissions into the future. The Strawtegi CO2ttage team provided building expertise and encouragement all along the way, and included Resource Engineering Group, Love Schack Architects, Community Studio and Peterson Associates Construction. Project goals included open-source sharing of project details and results, a call for proactive climate action and innovative problem-solving from design and building professionals everywhere. Building with rapidly renewable, carbon-sequestering materials capitalizes on Earth’s processes to clean our atmosphere and locks carbon into a structure for its lifetime. When the life of the building is over, in a hundred years or more, the materials can go back into the ground as organic matter, completing a full life cycle for those materials. The intentional use of key biogenic materials in the Strawtegi CO2ttage building envelope results in a measured 5,000-ton net negative CO2 carbon footprint, which is roughly equivalent to removing one gas-powered car off the road for a year. Third-party carbon calculations for the project were provided by Builders for Climate Action using the BEAM Estimator tool. This free online application supports easy comparison of the environmental impacts of various materials, so design teams can explore the Global Warming Potential (GWP) effects of their choices early in the design and decision‑making processes. Carbon sequestered within the chopped straw insulation in the walls is a key factor contributing to the project’s net zero carbon footprint. Straw is an abundantly available agricultural byproduct that provides a viable form of natural cellulose insulation that could become increasingly useful to replace nonrenewable materials. This project used locally produced straw, chopped and densely packed between MSL Sonoclimate Eco 4 wood fiberboard structural sheathing which provides continuous R-4 insulation at both the exterior and interior wall panels. This sheathing and straw insulation produces a unique structural insulated panel (SIP) that significantly exceeds energy code requirements. The modular design of these SIPs allowed for efficient prefabrication in an indoor space with just 40 labor hours. Onsite assembly of the rough building shell took only five days. Although many straw panel projects exist in Europe, Strawtegi CO2ttage is the first permitted structure of its kind in the U.S. to be insulated with chopped straw. Locally produced hemp batt insulation in the roof assembly is another significant material contributing to the project’s negative carbon footprint. Hempitecture’s bio-based Hempwool provides R-3.7 per inch, is treated with non-toxic natural fire retardants, and is available in a variety of thicknesses to fit standard framing with spacings of 16 or 24 inches. As a commercial product, Hempwool has a negative carbon footprint, meaning that it offsets and stores more CO2 than is emitted from the manufacture and installation of the product. Manufacturing and distribution facilities are located just north of Utah in Jerome, Idaho. Hempitecture will soon be introducing ground-breaking new products including the PlanetPanel, Hempwool+ and more. Wood is also a carbon-sequestering material when it is sustainably sourced, and all wood products on this project were carefully selected. The contractor was surprised that three of the five primary lumber suppliers in the Salt Lake Valley declined to bid on this project because they do not offer FSC (Forest Stewardship Council) or SFI (the less rigorous, Sustainable Forestry Initiative) certified products. After being dismissed and told that “It’s all sustainably grown these days,” the team diligently hand-picked select batches of lumber from various yards where certification labels and stamps were clearly visible. They found Home Depot to be one of the fastest and easiest suppliers where FSC certified lumber was consistently available. 24 REFLEXION
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