Many homes on Cape Cod are clad with cedar shingles, but I’m confident none were built like the one that my company, Cedarworks, recently sided. As part of the homeowner’s goal to reduce the project’s embodied carbon—the upfront CO₂ released into the atmosphere as a result of the construction process (see “A Builder’s Guide to Carbon-Neutral Building Practices,” )—general contractor C.H. Newton Builders of West Falmouth, Mass., had sprayed the walls and roof with hemplime insulation.
Hemplime (or hempcrete) is made from the hemp plant’s woody core, a lime-based binder, and water. On this house, it took the place of sheathing, housewrap, and spray-foam insulation. The mixture is sprayed into the framing cavities from the exterior after battens have been nailed to the interior surfaces of the studs. The result is a low-carbon, airtight wall assembly with an R-value of about 2.5 per inch that can be finished with lime plaster or, in this case, vapor-permeable cedar shingles over a rainscreen assembly (learn more about this project at capecodhemphouse.com, and about hemp as a building material at US Hemp Building Association, ushba.org).
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