Tradical Hemcrete, a combination of hemp chips and lime-based binder, is the wall material of choice for a group of builders and designers in North Carolina.
Fabrics and rugs made with industrial hemp are often cited as acceptably green alternatives to floor coverings made from petrochemicals, or to woolen rugs treated heavily with insecticide. But hemp also has found its way into another domestic application.
And it is not the first alternative use that may come to mind.
Nauhaus Institute, a North Carolina-based coalition of designers, engineers, builders, developers, and others devoted to green construction, has been working with hemp as a wall-construction material. Called Tradical Hemcrete, the material is essentially a lime-based binder and industrial hemp chips (derived from the woody, pretty much unsmokable core of the hemp plant) that, when mixed with water, can be sprayed over a substrate on an exterior wall or poured into forms around timber or stick framing to create a thermally resistant but “breathable” barrier.
A wall-material bakeoff
As noted in a recent story in Asheville, North Carolina’s Citizen-Times, Nauhaus (pronounced “now house”) has two homes under construction that will feature Hemcrete walls. Nauhaus says on its website that, overall, hemp met sustainability, performance, cost, and aesthetic criteria better than competing materials.
“On the natural building side, we feel that earthen mixes don’t have adequate thermal performance in our climate while the vulnerability of straw bales to water damage concerns us,” the group’s partners say on the Nauhaus site. “On the high-performance commercial side, we are skeptical of the long-term durability of SIPS walls and feel that double-stick frame systems are too complex and prone to air infiltration weaknesses. These and other problems seem to be solved by what to us is a new material: Tradical Hemcrete.”
Hemcrete also is billed as insect- and fire-resistant. One issue the group couldn’t get around, however, is that, while industrial hemp products can be imported into the U.S., it is illegal to grow hemp here. Tradical Hemcrete is made in the U.K. by a division of Belgian firm Lhoist Group, a specialist in calcined-limestone products, and is distributed in the U.S. by Hemp Technologies, of Asheville.
A green quandary: shipping from the U.K. The Citizen-Times story points out that shipping costs make Hemcrete considerably more expensive — the approximately 1,900 sq. ft. of Hemcrete required for one of the Nauhaus projects, with 3,100 sq. ft. of interior space and 12-inch-thick exterior walls, costs about $56,250. But Hemcrete walls also require less lumber, which reduces framing costs 30% to 40%, Greg Flavall, a co-founder of Hemp Technologies, told the paper. Another advantage to Hemcrete, says Nauhaus partner Chris Cashman, is that it serves as “your Sheetrock, insulation and Tyvek all rolled into one.”
Building-performance costs in both Nauhaus projects will be significantly lower than conventionally constructed homes of comparable size, although the smaller of the two structures, a 1,450-sq.-ft. four-bedroom that will serve as a Nauhaus prototype and test house, will have 16-inch-thick walls and solar panels on the roof to bring energy usage to net zero.
Not surprisingly, Nauhaus partners advocate legalizing industrial-hemp growing in the U.S. “Our feeling is, what a great crop this would be for North Carolina’s tobacco growers to get into,” Nauhaus partner Tim Callahan told the Citizen-Times. “Bringing this in from England is probably not the greatest idea (economically). If local farmers can benefit from this, it would be great for them and great for the economy.