Builder Spotlight: Zach Popp Turned a Moldy Bedroom Wall Into America's First Code Evaluated Hempcrete Panel
Fourth in a USHBA series on the architects, engineers, builders, and material innovators actually putting hemp buildings up in this country.
By Shawn Ledig, President, U.S. Hemp Building Association
Zach Popp did not set out to start a building materials company. He set out to find out why his daughter was sick.
In 2010, Popp moved his young family into a house in Wittenberg, in north central Wisconsin, that had been built in 1997. That first winter, his infant daughter was sick for three or four months straight. "Constant respiratory issues, runny nose, you name it," he told USHBA. The family chalked it up to a new town and new germs. Then one day he walked into her bedroom and saw small black spots under the window. The carpet was soaking wet.
The north facing window had ice dammed through one freeze and thaw cycle after another. The meltwater could not get out through the window's weep holes, so it backed up into the wall. When Popp cut out the drywall, mold covered the wall four or five feet up, all the way across. He had grown up framing houses alongside his father, a builder, so he understood exactly what had happened inside that wall. The moisture had nowhere to go (Green Bay Press Gazette).
“Homes shouldn't hurt people.”
"That was the first thing that came to mind when toxic mold in the walls of our home made my daughter sick," Popp writes on the company's website (Sativa Building Systems). That winter started a search that has since produced a patented precast hempcrete panel, the first hempcrete product in the United States with an ICC Evaluation Service report, a working factory, a line of tiny homes, a Canadian manufacturing partner, roughly $2.1 million in U.S. Army research contracts, and a 4,000 square foot family home built with his own product.
Playing Mad Scientist in the Garage
"I thought, man, maybe there's something out there that could have prevented this," Popp said. "What if there's something that would have let the moisture out of the wall? Or what if there's something that just is generally more mold resistant?"
His research kept leading back to hempcrete. It checked every box: breathable, mold resistant, fire resistant, pest resistant, and rot resistant. He also saw why it was not more common in American construction. Cast in place hempcrete is labor intensive, and it can take six to eight weeks to dry on a job site (Green Bay Press Gazette).
Popp was in no position to quit his day job. "I had a young family. I needed some of the stability of a normal job," he said. "So I just kept working my jobs and kind of playing mad scientist in my garage when I had time."
His answer was to move the wet work off the site. Tamping hempcrete into forms on the job, he decided, was not the way to truly scale the material. His first idea was a full height, eight foot wall panel. Every time he tried to tip one up, he would bump it and material would crumble out. So, he took the same 16 inch wide section and cut it down to just two feet tall, with a shape that interlocks with the studs. "I'm like, then maybe I'll have something here," he said (Green Bay Press Gazette, Sativa Building Systems).
He built his own forms in the garage and, working nights and weekends with a tiny mortar mixer, cranked out a first batch of about 80 panels by hand. "It was a nightmare," he said, laughing. One of his daughters had just been born. "My wife had a new baby, and I'm out there in the garage making Z Panels by hand."
His early testing was just as hands on. He cast six-inch cubes and stacked weights on top to see which ones crumbled. "I didn't know anything," he said. "I'm like, well, let's just test strength this way." He had two goals from the start: make a product that worked, and make it from American materials. Back then he had to import his hemp from Europe, and some of the industry's early builders were importing their binders as well. Popp did not want to import both. He started with hydrated lime, experimented with pozzolans including metakaolin and pumice, and settled on pumice as the strongest option.
The first thing he built with those garage panels was a small greenhouse, put up in January in Wisconsin. That is when the biggest advantage of precast hit him. "You could build in the winter," he said. "You don't need to let it dry out. It's pre dried. I dried it in my garage."
Precasting also meant quality control, with the same amount of hempcrete in every panel, and no waiting on the job site. "We set up these forms, we tamp it, and then we let it dry out for how long? Well, might be a month or two or more," he said. "That's a long time for a construction project, where people often want to keep things moving."
“If we do precast, then we can have more quality control. We ensure that every single product has the exact amount of hempcrete in it.”
In 2018, Popp filed a provisional patent and formed Sativa Building Systems, named for Cannabis sativa. A U.S. utility patent followed the next year (Green Bay Press Gazette). That first greenhouse has stood through multiple Wisconsin winters and at least one tornado (Sativa Building Systems). "When I finally made that greenhouse and it stood through a tornado or two," Popp said, "I'm like, this is something."
From there he took a slower road than much of the industry. "My approach has always been, let's validate this product first and actually kind of slowly phase into the market," he said. He is quick to add that he does not knock any other method of hempcrete construction. "Everyone's going to have a preference. But I do think that there's some pretty big advantages to prefabricating."
How the Z Panel Works
"It is essentially a hempcrete block panel that doesn't need to be load bearing because it works with standard wood or steel framing," Popp told The Business News. "And it's a precast product, which means it doesn't have to do any drying on the job site. It shows up pre dried" (The Business News).
From an engineering standpoint, the Z Panel is honest about what it is. It is not structural concrete. It is a nonbearing hempcrete wall component that works with a code approved frame, which is exactly how hemp lime should be presented to building officials. Sativa markets the panel for wood or steel framing, but its ICC-ES report specifically covers light frame wood walls, so builders relying on the report for plan review should frame in wood.
According to Sativa's published specifications, each panel (Sativa Building Systems):
Size: 24 inches tall, 12 inches thick, and 16 inches wide on the exterior face, with a 14.5 inch interior width. The ICC-ES report lists the evaluated Z Panel 2.0 at 12 inches thick, 15.75 inches wide, and 25.5 inches tall (ICC-ES).
Weight: 45 to 55 pounds, depending on humidity, so one person can set it by hand.
Framing connection: Recesses on one side fit around 2x4 or 2x6 studs. Recesses on the top and bottom interlock with the bottom plate and adjacent panels, giving flush interior and exterior faces.
Fastening: An embedded 2x4 on the interior attaches the panel to the studs. A newer embedded vertical wood strip on the exterior provides attachment for siding or cladding.
Replaced materials: The panel takes the place of exterior sheathing, vapor barrier, insulation, and gypsum board.
Binder: Sativa's proprietary binder replaces costly imported hydraulic lime with locally sourced hydrated lime and a strengthening additive (Sativa Building Systems FAQ).
The company reports a Class A rating under NFPA 286, 145 mph wind load resistance under ASTM E72, compressive strength of 26.4 psi under ASTM C109, an R value of 21, and thermal mass performance it describes as equivalent to R30. Each panel is reported to sequester 1.1 kg of CO2e (Sativa Building Systems). Z Panels currently sell for $65 per unit, Popp told USHBA.
Popp is clear about what the patent does and does not cover. "Hempcrete as a material we have not patented," he told CEOCFO Magazine. "What we have patented is the shape, functionality, and mix ratio" (CEOCFO Magazine).
The panel's size came straight from his father's job sites. Popp started working on his dad's three man framing crew at 14, and his father avoided cranes whenever he could. They were expensive, they added complexity, and they could be dangerous. "We would set trusses without cranes. We'd do everything we could without a crane," Popp said. When it came time to size the Z Panel, his test was simple: "I'm like, I can lift this."
He is just as direct about where the panel does not belong. People ask whether Z Panels can go in ceilings and floors, and his answer is no. In a ceiling, the weight adds load to a roof that, in Wisconsin, may already be carrying four feet of snow. "There's a reason why people blow in fiberglass and cellulose insulation into an attic," he said. "It's light, and you get a lot of R value per inch." The panels are not great for retrofits either. "I'm not going to lie to them and say, oh, yeah, you can use them anywhere," he said. "They're great for new construction exterior walls. That's what they're great for."
A Code Report That Reaches All 50 States
For anyone who has stood across the counter from a building official with a hempcrete wall section in hand, this is the part of the story that matters most.
Sativa began pursuing its own ICC-ES evaluation report in 2022. Around the same time, Popp joined USHBA and learned that the hemp lime appendix was headed into the 2024 International Residential Code. He seriously debated whether a product report was still worth the expense, since the appendix already includes provisions for blocks and panels. But adoption varies state by state, and Wisconsin does not adopt the IRC at all. "We do our own code," he said. "So I'm like, you know what? I'm still going to do this." He brought in investors to help cover the cost.
"It's very, very, very costly, but I learned a ton," Popp said. "My background is construction. I surrounded myself with some good people who could help me." The timeline stretched, too. "I hate to say it, but the ICC-ES team may be a little too optimistic at times and say, this is a six month journey, but really, it's a year, year and a half."
The work paid off. Sativa completed the ICC-ES process in December 2024, and the report, ESR-5073, was issued in January 2025 (ICC-ES). On February 28, 2025, the company announced that the Z Panel had become the first hempcrete product in the United States to demonstrate compliance with the International Residential Code and International Building Code in all 50 states (Sativa Building Systems). "The completion of the ICC-ES Report for our Z Panel demonstrates that hempcrete is not only an environmentally responsible choice but also a code compliant, high performance solution for modern construction," Popp said in the announcement.
It is worth being precise about what that means. Appendix BL of the IRC gives jurisdictions a prescriptive path for hemp lime walls, but it only carries force where a state or local government adopts it. An ICC-ES evaluation report is a product specific document that building officials across the country already know how to read. The two paths complement each other. Appendix BL helps the whole category. A product evaluation report helps one manufactured product move through plan review in places that have not adopted the appendix. Sativa built that path for its own product, and every builder working with hemp benefits from having a hempcrete product inside that system.
The report also shows exactly how the product is meant to be used. ESR-5073 evaluates the Z Panel 2.0 under the 2021 IBC, IRC, and IECC for structural performance, interior finish, and thermal resistance. It covers the panel as a precast hemp lime infill for light frame wood walls in one and two story Type V buildings under the IBC, and it requires an engineered design under the IRC. The panel is made of hemp hurd, pumice, hydrated Type S lime, sand, fiberglass mesh, and water, with a tested R value of 1.75 per inch. The report classifies it as a Class A interior finish under NFPA 286, limits it to dry service conditions, and requires a weather resistive barrier and a code compliant exterior wall covering. Its fire resistance rating has not been evaluated, so walls are limited to non fire resistance rated construction. Supplements cover the City of Los Angeles, California, and Florida (ICC-ES).
That level of clarity is what building officials want to see, and it is a model for how every hemp product should be documented.
Tested by Fire
In the middle of the ICC-ES process, Popp's shop burned down.
Late on the night of July 28, 2024, neighbors alerted him that his Wittenberg warehouse and workshop was on fire. By the time he and his wife arrived, the building had essentially collapsed (HempBuild Magazine). It was a total loss. One pallet of Z Panels was not.
"When I looked into the building, I saw there was one pallet of Z Panels that was sitting there," Popp told HempBuild Magazine. "And those were all still mostly intact. You know, everything does eventually burn, but they retained their shape." The cellulose and fiberglass insulation in the building, he said, was completely gone (HempBuild Magazine).
His nephews had been working with him that summer, making panels and refining production. The likely cause, though it has never been confirmed, was the battery charger for a pallet stacker, the one thing left plugged in overnight. It appears to have shorted and thrown sparks into raw hemp hurd stored in the building, which is highly flammable.
The timing could have been far worse. Sativa had spent the months before the fire manufacturing product for every ASTM test its evaluation required, and the week before, Popp had shipped all of it to the labs. "There's never a good time for a fire," he said. "But if I were to pick a time to have a total facility loss from a fire, that was the ideal time, and I think it's just by the grace of God." None of the testing was held up. After the fire, he still traveled to Indiana to build the walls for testing and to Texas to build the room for the NFPA 286 corner burn test.
“There's never a good time for a fire. But if I were to pick a time to have a total facility loss, that was the ideal time.”
Popp called the fire "just another level of validation." "We're gonna come back even bigger and better," he said at the time. "That's the goal" (HempBuild Magazine). Sativa did exactly that. With enough financial runway to commit to rebuilding as fast as possible, the company had a new facility up and running by November 2024, Popp told USHBA.
People often ask whether the new building is made of hempcrete. It is not. "Unfortunately, we just needed the building first," Popp said.
From Lime to Mycelium
While the Z Panel moved through code evaluation, Popp was already working on what comes next, and it starts with the ceiling and floor question he refuses to fudge.
In 2023, Sativa won a $223,375 Army Small Business Innovation Research Phase I contract to compare its hempcrete against a new hemp mycelium material, a biopolymer grown with an edible mushroom culture that binds the hemp hurd as it grows. Popp had years of construction experience but no background in mycology, so he brought in mycologist Dr. John Holliday (Wisconsin Center for Technology Commercialization).
The Phase I results were strong. Compared with hempcrete, the hemp mycelium material showed comparable compressive strength, much better wood adhesion, 47 percent better thermal insulation value, and one third of the weight (Wisconsin Center for Technology Commercialization). Sativa also ran more ASTM testing than the Army expected, pushing the material as far down the research road as it could. Popp believes that effort helped win the next round.
In 2024, the Army awarded a $1,899,893 Phase II contract. Sativa is developing two products under it: a hemp mycelium insulation batt to replace fiberglass, and a hemp mycelium version of the Z Panel (Wisconsin Center for Technology Commercialization). Because the material cuts weight by more than 60 percent, it could go into ceilings and floors without adding the load that rules out hempcrete there (HempBuild Magazine). Several ASTM tests have come back promising, including a Class A fire rating (HempBuild Magazine).
The Phase II project wrapped up in September 2026. Popp is candid that the material is still early in development, with real challenges remaining in production and fungal resistance, and Sativa is pursuing a follow on project with the Army. In the meantime, he said, the contract has helped the company "do creative things, keep paying the bills," and keep moving forward.
Behind the research is a conviction that runs through all of Popp's work.
“It has to be because there is a real tangible benefit to people, not just, this is hemp, so it's cool. It's like, yeah, hemp's cool, I get it. It only gets you so far.”
From Tiny Homes to a Family Home
Before the code report came through, Popp needed a way to put panels to work. "When we were going through the whole ESR process, I didn't have a code compliant product," he said. "And I thought, what can we build that doesn't technically need building code inspections? And I'm like, tiny homes usually don't."
His first tiny home, about 220 square feet, is still one of the builds he is proudest of, because he did it alone. "I literally touched every single thing that was put into that home," he said. His little boys came to the shop with him every day to help. "I loved it."
Today the Cultivated Tiny Home is a tiny home on wheels designed as a healthy, non toxic refuge, including for people displaced by mold in their own homes (CEOCFO Magazine). One 24 foot wall is built from 11 inch Z Panels and acts as a thermal storage wall with an R value above 20 and roughly 3,000 pounds of mass. The all inclusive price is listed at $110,000 (Sativa Building Systems). HempBuild Magazine reported that the first unit sold with its panel system installed in about five hours (HempBuild Magazine).
Tiny homes also made business sense. Margins are strong, and roughly $5,000 worth of Z Panels that would otherwise be sold at a small profit can go into a tiny home instead. Popp also sees them as a path to ownership for young people, including his own adult kids, who are not going to take on a $500,000 mortgage.
“Home ownership is good. People actually like being able to plant their roots and be like, this is mine. It might be small, but it's mine.”
Tiny homes, though, only answered part of the question customers kept asking. "Have you done any larger residential projects?" Popp recalled. "I'm like, no, I really haven't. I've done additions, I've done tiny homes. I've done small stuff." So he decided to put his money where his mouth is. He financed and built his own home, roughly 4,000 square feet, as Sativa's first large scale Z Panel structure.
Every square foot will get used. "I got eight kids," he said, "so every square foot of this home is still gonna be filled with something." His family helped build it, too. His 22 year old daughter, Lily, installed probably 40 percent of the Z Panels herself.
“I built my own home with it. It works. Come here, test it, feel it, touch my walls.”
The house is also a cost test. "My goal was, we're going to build this for under $200 a square foot, because then we can say we're truly competitive," Popp said. When we spoke on October 29, the job was on the home stretch, with water on, plumbing fixtures in, and carpet, handrails, and baseboard trim going in.
Where Sativa Goes From Here
"We're ready to really fully launch this product deeper into the market," Popp said. But his plan for the next three to five years is to scale in proportion to demand, and he is refreshingly realistic about what that demand looks like. "I never want to be so optimistic and pretend that natural building or hempcrete construction will take 10 percent of the market," he said. "It's not happening in the next 50 years, probably. But we could start making some serious headway in more niche markets."
Sativa produces Z Panels in a 2,400 square foot facility, and the plan is to grow through licensing. Partners who can make a quality product and meet Sativa's standards would manufacture in their own regions, which is less capital intensive and opens a path to national distribution. "Not everything has to be then shipped out of Wisconsin," Popp said. Closer to home, the focus is on small production refinements that drive costs down.
The panel is also crossing the border. Hempcrete Homes Inc., based in Barrhead, Alberta, describes itself as the Canadian manufacturer of the patented Sativa Building Systems Z Panel (Hempcrete Homes Inc.). Popp confirmed the partner manufactures exclusively for the Canadian market.
Climate is part of that equation. Humid Wisconsin summers, made worse by what locals call corn sweat from the surrounding fields, slow drying at the plant. If he could pick an ideal place to manufacture, Popp said, it would probably be Arizona. Field experience in hot, humid regions like the Gulf Coast is still limited. "We haven't done a lot of field testing, but that's the goal," he said. "That's what we want to be doing more of, is just real projects." Next up is likely a small cabin on a Native American reservation near Sativa's home base.
Sativa also plans a Certified Installer Program for Z Panels and future products (Sativa Building Systems). It has not officially launched yet. Popp is building the training content and collecting an interest list, with plans for a hands on workshop and possibly a virtual option. For a product that has to go in a certain way to perform, that training matters as much as the panel.
Advice for Your First Hemp Build
I asked Popp what he would tell someone planning a first hemp project. He did not start with hemp. He started with a dormer.
"I don't know how many times we put a dummy dormer on a house," he said of his years framing with his father. "We spent a day building this dormer, and it is not functional. This was silly." His advice is to make the home beautiful and keep it simple.
“Maximize efficiency with simplicity.”
Then plan, and shop around. There are more options than ever for quality materials at reasonable prices. Windows sourced overseas may cost less. "As much as I like to buy from America, I get it, sometimes you have to get it from elsewhere," he said. Popp bought all the doors for his own house from Door Clearance Center in Texas.
"If you maximize simplicity, you plan, and you shop around, you can build with high quality stuff and be competitive with the price of your standard production home from one of the bigger builders in America," he said. "That's what I would encourage anyone to do."
Why This Matters for the Rest of Us
Popp named the industry's biggest obstacle plainly. "Awareness is the ongoing challenge," he told HempBuild Magazine. "Potential customers often have to sort through products that are in an idea stage from those that are market ready. This can cloud the market, and make it more challenging for businesses that are ready to serve customers to actually reach them" (HempBuild Magazine).
The awareness gap reaches all the way to the bank. Popp once sought a $25,000 loan to bridge a gap between contracts. A banker at Associated Bank was enthusiastic until it came time to approve it. Then the loan was denied because of the business's cannabis association. "I'm using a secondary product, no THC," Popp said, "and it didn't matter." Hemp builders and processors across the country, including here in Louisiana, have hit the same wall.
Sativa has done the work that separates a market ready product from an idea. There is a patent, a factory rebuilt after a fire, published test data, a code evaluation report, a manufacturing partner, federal research funding behind the next generation of the product, and a family home anyone can walk through and touch.
The story also lands close to home on the Gulf Coast. Sativa has framed Z Panel housing as a resilience tool for flood prone communities, where mold resistant walls can help families return home with less remediation after a disaster (Climate Curve). Anyone who has gutted a flooded house in Louisiana understands why that matters. So does anyone who has tried to permit a hemp home in a state that has not adopted Appendix BL. Until that changes, a product with an evaluation report that building officials already know how to read is one of the most practical tools a builder can bring to plan review.
It all started with one bedroom wall and a father who wanted to know why it failed.
Sativa Building Systems is a corporate member of the U.S. Hemp Building Association. Learn more at sativabuildingsystems.com.
Know a builder, architect, engineer, 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
Green Bay Press Gazette, "When he's not working at Midstate Tech or raising seven kids, Wittenberg man is making walls from hemp and building a business", June 17, 2022.
ICC Evaluation Service, "ESR-5073: Sativa Building Systems, LLC, Sativa Z Panels 2.0", issued January 2025.
Zach Popp, email correspondence with the U.S. Hemp Building Association, October 2026.
Zach Popp, interview with the U.S. Hemp Building Association, October 29, 2026.
Sativa Building Systems, "About Us".
Sativa Building Systems, "Z Panels".
Sativa Building Systems, "FAQ".
Sativa Building Systems, "Sativa Building Systems Achieves Historic Milestone with ICC-ES Report for Z Panel", February 28, 2025.
Sativa Building Systems, "Sativa Building Systems Secures $1.9M Army Award to Advance Bio-Based Insulation", December 4, 2024.
Sativa Building Systems, "Tiny Homes".
Wisconsin Center for Technology Commercialization, "Sativa Building Systems: Creating safer building materials with hemp-mycelium".
HempBuild Magazine, "Hempcrete Panels Survive WI Warehouse Fire".
HempBuild Magazine, "US Army Awards $1.9M Contract to Explore Mycelium-Hemp Insulation".
HempBuild Magazine, "Hemp Voices: Zach Popp, Sativa Building Systems", February 12, 2026.
HempBuild Magazine, "Sativa Building Systems" tag page.
The Business News, "Mold resistant, pest resistant, rot resistant, fire resistant".
CEOCFO Magazine, "Sativa Building Systems, Zach Popp", January 20, 2025.
Hempcrete Homes Inc., "Products".
Climate Curve, "Sativa Building Systems Inc".
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