ACRE is a sustainable new building material based on rice hulls that delivers the beauty of real wood but with increased performance characteristics.
BY BILL HENSLEY
MY FIRST TRIP TO JAPAN WAS A PARTICULARLY HOT SUMMER IN THE LATE 1980s. Actually, all summers in Japan are particularly hot, but having grown up on the California coast I was not prepared for the humidity that goes with the summer heat. My best reference was a couple summers in Cincinnati visiting with relatives. Hot and humid.
Tokyo’s Narita Airport sits well outside the city, surrounded by small towns and rice fields. And in the summer months those rice fields display a magical beauty easily visible during the long runway approach. Upon leaving Narita the rice gets closer, seemingly growing right up to the edge of the road.
Rice is a water-intensive crop, well suited for wet climates. In peak growing season rice paddies are flooded with a few inches of water. Modern irrigation makes growing rice possible in drier climates such as California’s Sacramento Valley region, although the increasing periods of drought in the Western United States will make this more challenging. Worldwide production of rice exceeded 500 million metric tons in 2021, with leading producers by far being China and India, followed by Bangladesh, Indonesia, Vietnam and Thailand.
The United States is not even in the top ten among global producers, but still accounts for over seven million metric tons of rice annually. Like all crops, rice is susceptible to weather and pests. Rice has developed a hard, fibrous outer layer – the hull, or husk – to offer protection. The rice hull is largely indigestible to humans, so it must be separated from the bran layer and kernel during milling. The hulls are high in opaline silica and in lignin. Lignin is also a key element in wood, accounting for roughly 30 percent of wood weight while giving it both rigidity and antimicrobial properties.
Sounds like a construction material? Well, yes. Incorporating rice hulls in clay bricks dates back many centuries. One example is the temples of the Batujaya Archaeological Site in Indonesia dating to approximately the 5th century AD. The bricks used in the site were a mixture of rice hulls and clay. But with that high silica and lignin content, there must be some modern opportunities to explore.
Meet ACRETM by Midern Mill
ACRE is a sustainable new building material that blends rice hulls with a mix of other ingredients to deliver the warmth and beauty of real wood but with increased performance characteristics. The company behind ACRE is Modern Mill, who promotes ACRE as “light, strong, water, pest and weather-resistant, and guaranteed not to rot, crack or splinter.” ACRE is a 100 percent tree-free wood alternative. It is produced in a zero waste environment in Fernwood, Mississippi, close to a major U.S. rice-growing region. The plant is also in a Department of Treasury Qualified Opportunity Zone. In an area where almost half the local population is living at the poverty level, Modern Mill is paying a living wage with benefits and educational opportunities. That investment is an important pillar in the company’s “great product, great for the community, great for the planet” philosophy.
100 PERCENT TREE-FREE
At the November 2021 United Nations Climate Change Conference, commonly referred to as COP26, over 100 global leaders committed to the goal of zero deforestation by 2030. Ambitious? Yes. According to Global Forest Watch over 99,000 square miles of forest were cleared in 2020 alone. To put that in perspective, it’s a larger area than the United Kingdom. Parts of the Amazon rainforest now produce more carbon dioxide than they absorb. The “lungs of the planet” are not as healthy as they used to be. With ACRE, Modern Mill hopes to “rework the calculus in favor of trees” by creating an alternative with true market appeal and sustainability as a core value.
“NATURE’S DISCARDED KEVLAR”
The vision behind ACRE was a “wood-free” wood alternative that could combine the easy maintenance of a composite with the workability and aesthetics of wood. The water, weather, rot and pest-resistant properties enabled by the rice hull’s high silica content that protect the tender grain make it the ideal building material ingredient. And the hull’s fibers deliver a “natural” wood grain appearance without any manufactured mimicry.
The finished product is available in multiple forms from trim boards, to decking, siding and sheets. So far, trim is the most popular category, mostly window trim and fascia boards. Sheets in sizes one-quarter to one-inch thick, and four-foot wide by eight- to twenty-foot lengths are the next most popular output, delivering a high-grade hardwood look and feel. ACRE can be left unfinished or can be finished similar to wood products with oil, stain, lacquer or paint. Factory finishes are also available.
And, it is gaining traction in the market. One company embracing ACRE is San Diego based KIRE Builders, Inc., which specializes in new construction market-rate multifamily apartments. “As a developer, builder and operator we are always looking for innovative products that can provide low maintenance solutions, to decrease operating expenses and add to the overall longevity of the project,” said KIRE Chief Operating Officer Adam Hutchinson. “We use the ACRE Sheets for fencing and exterior applications to achieve the look and feel of natural wood that is perfectly aligned with our focus on sustainability. ACRE is a great wood replacement option, and we look forward to using it more in the future.”
To learn more, we spoke with Modern Mill Strategic Account Manager Chandler Delinks, and started with the basics.
BILL: Let’s start with the origin of ACRE: Why rice hulls? What holds it together?
CHANDLER:The wood alternative industry has been trying to achieve the optimal balance of wood aesthetics and durability. The key to ACRE is that it is more than 50 percent rice hulls, and the fiber in the hulls have that natural wood look. They take a long time to degrade which makes for exceptional performance.
BILL: Describe the manufacturing process.
CHANDLER:e start by grinding the rice hulls and then blending them into a “batter” with PVC and other ingredients. This gets injected into a die rendering it as a sheet, which then dries. At this point we become a mill, cutting the rigid sheet to final sizes. And it’s the sanding process that exposes the character of the fibers — the natural ACRE grain is similar to white oak, teak, Spanish Cedar or mahogany.
CHANDLER: Right, PVC has evolved, mitigating earlier issues. Additives like cadmium base and lead base are no longer used. ACRE is made with rigid PVC, which does not use phthalates or Bisphenol A. Working with ACRE is technically respirator-free. This is because of the rice; the heavier shavings create less airborne particles. In the mill we capture the dust, and it reenters the product stream. It’s a closed loop and zero waste. And less waste on the jobsite, too. We anticipate post-consumer recycling, but this will require separate containment.
BILL: You mentioned becoming a mill; does ACRE cut like wood on the jobsite?
CHANDLER: It does. Remember it’s more than 50 percent rice hulls. It’s not hard on your tools like some wood alternatives. By basing the material on the rice hulls, we are addressing a number of pain points: ACRE expands and contracts less than other wood alternatives. It takes screws and nails better, with no predrilling required and no flaring at the screw point. And there is none of the static charge that’s associated with PVC wood alternatives. Really, builders no longer need to make concessions.
BILL: Can you elaborate on the character of the fibers exposed during sanding?
CHANDLER The standard sanding process in the mill delivers a “grain” look ideal for trim, siding and other applications. But it can be sanded to a cabinet grain finish. It’s exceptionally versatile. A millwork company we’ve worked with has even wire-brushed it to bring out more of a natural patina. And it can be used in a thermo form to produce special curves — this can be done on-site, not just in the factory.
You don’t need to prime ACRE, and it can have ground and water contact. But you can stain like wood. Stainability is one of the exciting aspects of this. We hear that “nobody stains anymore” but actually people do stain, and they want the freedom and the design options that stain creates — they just don’t want all the prep and maintenance. With a lot of the natural woods used in the coastal communities — particularly cedar and mahogany — they are durable but need oil priming and two coats of oil finish. ACRE needs no priming and only staining to visual taste, so the time and cost savings are substantial.
We’re supplying a builder working in Martha’s Vineyard, Cape Cod and Western Massachusetts whose customers are building four million dollar second homes. Vertical Grain Cedar (VGC) was the wood of choice, but is getting too pricy. The builder hadn’t felt there was a true replacement to VGC for trim and siding, until now. So while we started as a complement to PVC, we are now replacing VGC, Ipe and mahogany because the aesthetic is so strong.
BILL: Let’s talk about builders. What are the major factors influencing builders who are working with ACRE?
CHANDLER: Consider three builder types, based on the types of wood or wood alternatives they primarily use: The Wood builders like the one I mentioned are using cedar, mahogany or similar. Builders using PVC wood alternatives are also a big market, and then there is fly ash polycarbonate. Builders using each type make concessions they have learned to tolerate. For the “Wood guys” price is an issue, along with the wood quality going down. For them, our aesthetics are the driver, but what’s also important is that while we do expand and contract more than wood, it’s less than PVC. And then there is the stainability I mentioned before. All things considered; this is the “market changer” for the wood lumber industry.
Feedback we get from the fly ash polycarbonate users includes concerns about safety due to the dust, plus breakage on jobsite, wear and tear on tools, that two people are required to carry it, and that it adds to jobsite waste. But it expands/contracts less than PVC, which is a plus. With ACRE the expansion and contraction is between fly ash and PVC, so we hit that point. And it’s easier to work with — one person can carry it and it’s less wear and tear on your tools.
The PVC builders typically start with the question “how much does it expand and contract?” ACRE is about 15-20 percent less than PVC which is important for performance. And they ask if there is mushrooming at nail and screw locations, to which we can confidently reply “no.” That’s a big plus for the finished look.
For all three builder profiles, it’s the ACRE “wood aesthetic” that seals the deal. Every time we send samples, we know the response is going to be great.
BILL: Speaking of the aesthetics, what is the response from architects?
CHANDLER: This has traditionally been the longest sales cycle, but now it’s often “I have a project right now.” That means decisions are going to happen quickly. Innovation is important as well. What we hear from architects is that they want the features and benefits of real wood, but no previous wood alternatives truly captured the aesthetics. One recent example was an East Coast architect working between Montauk and Fire Island — we sent samples, answered a few questions, and got approval from all parties. The response was “this is better than wood.” Perhaps we can summarize the ACRE value proposition for architects and designers as design opportunity, sustainability and performance. From cabinetry to siding to the thermo form curve I mentioned earlier — these are all made from ACRE.
Sustainable upcycling is important related to LEED certification; this is another important box we check. And again, we see reduced waste on the jobsite, which is good for everyone. Sustainability is particularly important to the Gen Z homebuyer. Gen Z is leaning toward smaller but higher quality, and as a group don’t know as much about maintenance which makes an ACRE house all the more attractive.
The rice harvest happens every year, and the hulls that remain after milling represent a significant environmentally friendly building resource, one that Modern Mill is just starting to tap for ACRE. Unlike forests that can take decades to grow back, the rice harvest is an annual event, a renewable source of upcycle opportunities for agricultural technology innovation.