В Массачусетсе построили экологичный дом из конопляного бетона с использованием государственной программы льготных кредитов

GREAT BARRINGTON — Maria Murillo is building an apartment out back. And she’s filling its walls with hemp. Not marijuana, exactly, and not bales of the stuff. Murillo is using hempcrete, a mixture made from the woody interior of industrial hemp plants, limestone-based binder and water, to insulate the exterior walls of the accessory dwelling unit, or ADU, taking shape beside her home on 146 Christian Hill Road. For Murillo, the choice was about more than keeping the building warm. “Sustainability has always been in my heart,” she said. Despite the name, hempcrete is not a support or structural material like concrete. It is an insulator that keeps in heat and wicks moisture. The material is filling the walls of Murillo's ADU, which she financed in part through a state program. "I've learned such a trade here," Murillo said, who is a mom and a client care coordinator in in‑home services, as she's bolstered her skills working with the team setting hempcrete. 2 min to read Hemp, while still the same species as marijuana plants, has a different chemical makeup, a lower concentration of the psychoactive compounds and is grown in dense fields. When it grows, it absorbs carbon dioxide and greenhouse gases.  Hempcrete earned its moniker because of the process used to make it, not the function it serves. To make it, the woody, inner stem of the hemp plant is broken down, mixed with a binding agent (this build used one derived from limestone) and water. The result is a fibrous mixture that looks like a mix of large pieces of shredded paper and wet wood chips. That process doesn't impact the environment to nearly the same level producing concrete and insulation does, said Tom Rossmassler, founder of HempStone, the company adding hempcrete to Murillo's ADU. The volume of greenhouse gases hemp pulls from the air offsets the negative environmental impact of producing hempcrete, he said. HempStone, based in Northampton, was launched in 2018 and has built homes on Cape Cod and in Goshen. It also built several farm worker cabins in New York.  Once the hempcrete is put in place and sets, it acts as an insulator, Rossmassler said. Murillo's 12-inch wall will be rated at an insulation efficiency of R-24 when completed. In Berkshire County, wall cavities need to be rated to R-20 or higher. Traditional insulators, like fiberglass or sprayed cellulose, have an efficiency rating that top out at R-3.8 per inch, whereas hempcrete's is R-2 per inch, but Rossmassler said the material performs better than that rating. Every additional inch of insulation adds another 3.8 to the wall's R-value, so it would take more than six inches of traditional insulation to match hempcrete's rating. Despite the wall being 12 inches, Murillo's ADU uses cheaper two-by-fours because the hempcrete can support its own weight, allowing it to go around the support beams, not just in between them. Despite being statically more inefficient, hempcrete does give some advantages, including the lack of gaps or places to leak heat, Rossmassler said. That's not the case in traditional insulation, causing it "to function at 50 to 75 percent" efficiency.  On top of insulating, "this material actually absorbs moisture, water vapor out of the air, and then releases it and balances out the humidity," Rossmassler said. That further regulates heat and is something other insulation doesn't do. "When it's really wet and cold, it feels colder. And when it's warm and moist, it feels hotter," he added. Although hempcrete does cost more than traditional insulation, it serves multiple functions at once, negating some fringe costs, Rossmassler said. "So in a place like Massachusetts, where the energy codes are so strict and are so intensive, it does make a lot of sense," he said. The hempcrete will become the core of the exterior walls of Murillo's ADU, filling the gaps of the wooden frame, but it will eventually be covered in a lime-plaster solution, Murillo said. Murillo started construction last November, setting the foundation before pausing work until spring. The hempcrete installation started last Monday and should be finished by Friday, Rossmassler said. The ADU should be completed before or around Thanksgiving this year, Murillo said. She built the unit so her father living in Costa Rica can visit with ease, and, in the future, Murillo herself could move in to it.   Murillo started by self-funding the project while she waited for Massachusetts to launch the Accessory Dwelling Unit Loan Program. Murillo said she was the first to apply for a loan through the program. That program gives loans of up to $250,000 for detached ADUs and $150,000 for attached units to low- to moderate-income families. The program lowers the functional interest rate, with MassHousing, the agency running the program, giving out loans at 5.25 percent. The lower-interest loan is part of a statewide push to build more ADUs, as the units are a tool Gov. Maura Healey sees as a way to inject new units into Massachusetts' housing stock as it tries to build 222,000 units before 2035. Despite several incentives being launched by the state to build these units, the county has only approved 16. Berkshire County makes up 1.8 percent of the state's population. Interest rates on 30-year mortgages sit above 6.5 percent. Home equity loans, which is how many ADUs are financed, are even higher, eclipsing 7 percent in most scenarios. Murillo's loan was the guinea pig for how the program is going to work, she said. "They had to get a lot of ducks in order, so hopefully my process will help others," she said. Since Murillo had already completed some work on the ADU, she took out a loan for $160,000. She estimated the cost of the project to be around $250,000, plus her own labor excavating the foundation, setting it and building out the hempcrete walls.  Murillo said one has to be hands on: "You just have to make this time to do this." She wasn't alone in building the ADU. Her partner, daughters and friends have all pitched in labor. For Murillo, that community aspect of the build gave her "goosebumps." "It's like how they used to build barns back in the day," she said, "when the whole community would come together and build a barn for each and every person."