Is Cannabis in Your Walls?

As the search for sustainable home building materials expands, some are looking at a head-turning option: cannabis. The use of industrial hemp, the name for cannabis that contains less than 0.3% THC (the psychoactive compound in marijuana), in construction is expanding around the world:

• Residential and commercial buildings constructed with hemp blocks and hemp panels have been used in Europe for decades. 
• In June, Cape Town’s Hemp Hotel became the world’s tallest hemp building.
• Since the approval for hempcrete in U.S. residential construction in October, interest in the green solution is on the rise in America as well.

Attendees of the Construction Liability, Risk Management, and Building Materials Committee meeting at NAHB’s recent Spring Leadership Meetings had the opportunity to hear from Bob Escher, AIA, the founding president of the US Hemp Building Association and the architect of the first permitted hempcrete structure in Denver (2017), and Jacob Waddell, president and founder of the Hemp Building Institute, the former executive director of the U.S. Hemp Building Foundation, and the former president and executive director of the US Hemp Building Association. Their presentation highlighted the benefits of hemp and its potential impact on the U.S. construction industry.

Why hemp? Escher provided a pictorial history of building construction with hempcrete, up to and including a new 2,600-square-foot, three-bedroom house in British Columbia, on the market for $1,990,000. According to Escher and Waddell, the material’s biggest appeals are its low embodied carbon properties, use as a healthy building material, and its sustainability. They stated that the main challenge ahead is setting up the processing infrastructure to get harvested hemp from farmers to the market. 

Hempcrete, which is made by mixing the woody core of the plant, water and a lime-based binder, reduces gas emissions and absorbs carbon, per BBC. It’s also fire and mold resistant; hygroscopic (absorbs moisture); non-toxic; and doesn’t utilize volatile chemicals or fossil fuel-based components. Hempcrete also holds a high pH, preventing mold growth. These features make it a handy building material for non-load-bearing insulation in walls, floor systems, ceilings and more.

According to Waddell, the plant can also be used for a multitude of building and home improvement purposes. As noted to the committee, HempWood has the durability of traditional oak and can be used to make benches, shelves, cutting boards, trim, window frames, dressers and tables. Hemp Batt Insulation, made from hemp bast fibers, is comparable to fiberglass, mineral and sheep wool. Hemp seed oil can create finishes on wood floors, furniture, trim, cupboards, tables and doors. Hemp can be used for carpeting, curtains and wallpaper, too.

Most important, unlike some of its alternatives, hemp is renewable. Hemp blocks also allow for simpler construction. Per The New York Times, 20-30% of a typical production schedule can be shaved off without the need for significant drying time or cement joints.

The committee will continue to work with the US Hemp Building Association and the Hemp Building Institute to educate itself on this emerging building product. Stay abreast of the latest developments at the Construction Liability Resources page.

Hemp was also one of the innovative solutions on display at the recent Innovative Housing Showcase. See this year's exhibitors.