Builder Spotlight: Tom Rossmassler Is Building New England's Hemp Homes One Wall at a Time
First in a USHBA series on the architects, engineers, and builders actually putting hemp buildings up in this country.
By Shawn Ledig, President, U.S. Hemp Building Association
Tom Rossmassler wore a hemp vest to his brother's wedding in 1997. That was his first real contact with the plant, and it stuck. Two decades later he started HempStone, LLC, a design-build firm out of Northampton, Massachusetts, that is now one of the busiest hempcrete builders and consultants in New England. He also sits on the U.S. Hemp Building Association board as a member-at-large (HempBuild Magazine, Hemp Voices). His title is “Chief Embodied Officer,” his own spin on CEO, and his email signature says “Hemperor,” which tells you most of what you need to know about him.
From Insulation Co-ops to Embodied Carbon
Tom did not come to this through hemp. He has been in construction and real estate since the early 1990s, pushing clients toward local, natural materials long before anybody on a job site was saying “embodied carbon” (Let's Talk Hemp). He started out in commercial real estate appraisal and acquisitions for institutional investors in Boston, then moved west, still in Massachusetts, and worked as an affordable housing developer. There he started the Green Affordable Housing Initiative, using $2 million from the state and $200,000 from The Home Depot Foundation to put solar on dozens of affordable housing projects across western Massachusetts, with the condition that each project meet enhanced green building standards. His work with the Northeast Sustainable Energy Association, where he is a lifetime member, is where he picked up Energy Star, LEED, Passive House, and the Living Building Challenge, through that network and the Building Energy conferences.
In 2009 he founded Energía, a worker-owned insulation co-op that installed cellulose, foam, rockwool, denim, and fiberglass in houses, commercial buildings, and institutions. That work put the co-op on the East Coast's first Living Building Challenge project in the regenerative built environment (Let's Talk Hemp; HempStone). In 2015, finishing an MBA in sustainability, he wrote his capstone on a business plan for a hemp-processing facility in New England. Then he went to Europe, met the International Hemp Building Association, and spent time with hemp builders in Italy. That trip settled it for him: the material could hold up under building science and could scale. Still running a successful business focused on operational carbon, he founded HempStone in 2018 to go after embodied carbon.
“Hempcrete, among all carbon-storing materials, has the most ability to scale for impact,” he told Let's Talk Hemp. “Hemp building is a niche within a niche; hemp is a star for embodied carbon” (Let's Talk Hemp).
Signature Builds Across New England and Beyond
HempStone keeps its hands-on installation work inside a four- to five-hour drive of Northampton, and consults and supplies materials for natural-building projects nationally (Let's Talk Hemp). A few of the jobs:
Goshen Howland Hemp House (Goshen, Massachusetts): The first hempcrete home in Massachusetts. Village Carpentry built the timber frame; HempStone ran the hempcrete installation and the design details (Goshen Hemp House, HempStone). It was also one of the first hempcrete houses in the country to get a blower door test, and HempStone has tested most of its builds since. Give it the same attention to detail you would give any other building, and a hempcrete house will hit the air-tightness numbers in a strict state like Massachusetts, and certifying standards like Passive House Institute US (PHIUS).
Shadow Brook Farm hemp home (outside Bennington, Vermont): A small south-facing salt-box for Susan Beal and David Pearson, on a 235-acre former dairy farm the family has owned since 1899. Beal set heart-shaped rocks she had collected over decades right into the hempcrete walls, and the crew plastered around them. Tom later entered the finished house in USHBA's 2023 hemp home contest (HempBuild Magazine).
Hudson Valley vacation cabins (New York): Two cabins using a hybrid wall built to cut curing time, with precast hemp-lime block from Coexist Build on the inside and Americhanvre's spray-applied hempcrete on the outside. HempStone was the hempcrete general contractor and also brought in Earthen Endeavors for the plaster, including tadelakt in the bathrooms (HempBuild Magazine).
Beachfront hemp home (Harwich Port, Massachusetts, 2021): A 6,000-square-foot net-zero house on Cape Cod with hemp-lime wall and roof assemblies, put up with a high-production European spray system. It was the first project in North America to use that method (project profile: capecodhemphouse.com).
Murillo accessory dwelling unit (Great Barrington, Massachusetts): One of the first projects financed through the state's new ADU Loan Program. HempStone hand-packed 12-inch hempcrete walls, targeting R-24, in Maria Murillo's detached ADU. Tom put a blowtorch to a test panel on camera and showed the char stayed where the flame hit it. “In a place like Massachusetts, where the energy codes are so strict and so intensive, it does make a lot of sense,” he told the Berkshire Eagle (The Berkshire Eagle). As of this writing HempStone is finishing the pour, which Tom says will make it the first permitted hempcrete ADU in Massachusetts, and probably in New England, under the state's Affordable ADU Act (Rossmassler, interview for this profile, September 2026).
HempStone has hemp-insulated cabins delivered for farmworker housing in New York and several more projects underway across Massachusetts, Vermont, and New York, plus consulting on dozens of builds nationally. Outside New England, Tom has consulted with and trained Native communities in Alabama, Maine, New York, and Minnesota on building, growing, and processing hemp for vertically integrated housing operations. He has also taught hemp-building courses at Rhode Island School of Design, Yale, SAIC, UMass, and the Yestermorrow Design/Build School in Vermont (Let's Talk Hemp).
Building the Evidence Base, Not Just the Walls
Tom does not stop at the wall. HempStone ran R-value testing with UMass, with structural testing to follow, and has worked with other people in the industry on fire testing aimed at ASTM Class A, hourly fire ratings, and NFPA compliance, with Home Innovation Labs and other partners. That data is what gets this material in front of a code official.
He will not take credit for the code work alone. He was part of the coalition that got the ICC's Appendix BL into the International Residential Code at the hearings in Rochester, and he hands the credit around fast. “It takes a village,” he says, naming Jacob Waddell, Martin Hammer, David Eisenburg, Anthony Dente, Kiko Thibaud, Tim Callahan, Bob Escher, Henry Gage, Sally Warren, Anthony Neuron, Cameron McIntosh, and Ty Olsen for work most people never saw. He also testified in front of Minnesota's technical advisory committee with Anna Koosman and Danny Desjarlais to help push the state's hemp-building code language through, and again pointed at Hammer, Eisenburg, Dente, and University of Minnesota faculty as the reason it landed.
That same thinking shows up in his USHBA work. Tom served as one of our New England Regional Leaders alongside Jennifer Martin and Alex Escher, and he now sits on the board as a member-at-large, working the same education, testing, and advocacy priorities nationally that he works job by job in the field (HempStone; HempBuild Magazine).
Where the Industry Stands Now
I asked him how far hemp building has actually come. Here is what he said in September 2026:
“Hempcrete (hemp-lime) construction adoption in the US has been a game of inches, with fits and false starts and slow traction in the first few years since the 2018 Farm Bill finally broke open the industry. The US still lags the leading European players but is catching up fast. The adoption of the BL Appendix into the 2024 IRC, and several key subsequent state and local adoptions, is showing that a stabilized building code allows for a simplified and more efficient permitting process. Even states and jurisdictions who have yet to adopt the latest code are still referencing it as a guiding document when pursuing the traditional ‘alternate methods and means’ pathway that all hempcrete buildings have used to date, knowingly or not.”
He had more to say on testing, product commercialization, hurd standards and whether manufacturers can hit them, and where decarbonization and policy take us over the next five years. That is a piece of its own, and we will run it after this series, along with other people's takes on the same questions.
A Collaborator's Philosophy
Ask Tom what this industry needs most and he does not name a product. “I believe this industry needs to grow through collaboration,” he has said. “In other industries, people are protective of their territory. To grow this one we need to share information and work together. We want to scale up without selling out” (Let's Talk Hemp).
Good place to start this series. A guy who came in through insulation co-ops and sustainability work, then spent most of a decade proving wall by wall, from a Vermont salt-box to a Berkshires ADU, that hempcrete can meet some of the toughest energy codes in the country and store carbon while it does it.
Know a builder, architect, or material innovator who belongs in this series? Get in touch with the U.S. Hemp Building Association.
Onward,
Shawn Ledig
President, U.S. Hemp Building Association
Sources
Hemp Voices: Tom Rossmassler, HempStone, LLC, HempBuild Magazine. https://www.hempbuildmag.com/hemp-voices/tom-rossmassler
New England Builder Sees Huge Potential for Carbon Capture in Hemp Houses, Let's Talk Hemp. https://letstalkhemp.com/new-england-builder-sees-huge-potential-for-carbon-capture-in-hemp-houses/
Goshen Hemp House, HempStone. https://hempstone.net/goshenhemphouse
VT Owners 'Undaunted' Through Hemp House Construction, HempBuild Magazine. https://www.hempbuildmag.com/home/vermont-hemp-house
New Hempcrete Wall Technique Cuts Drying Time in Half, HempBuild Magazine. https://www.hempbuildmag.com/home/hempstone-blocks-spray-construction
Cape Cod Hemp House project profile. https://www.capecodhemphouse.com/
Take a look inside an ADU being built with hempcrete, The Berkshire Eagle. https://www.berkshireeagle.com/news/southern_berkshires/hempcrete-accessory-dwelling-unit/article_14c08d8b-d9ef-4601-be79-4275ae5fa086.html
HempStone, LLC. https://hempstone.net/
Shawn, thanks for a great article on a very impressive man. I especially like Tom's emphasis on cooperation among the players in the hemp-lime arena.
Another great article on another HempCrete OG!!