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Hempcrete has failed to outperform petrochemical-based foams in insulation performance, but can still be a viable replacement for traditional building materials in “net zero” sustainable buildings, researchers have found. experiments conducted at Kansas State University.
Graduate students in a one-of-a-kind seminar led by Michael Gibson, a professor in the university’s architecture department, examined the use of hempcrete in floors, walls, ceilings and roofs.
“There’s a steep learning curve with this hardware,” Gibson said. “Ultimately, we learned that hempcrete is a great material with great immediate potential for use in Kansas, especially with the growth of industrial hemp cultivation so rapidly,” Gibson said.
Net-zero buildings produce enough energy onsite to meet or exceed their total energy consumption and eliminate greenhouse gas emissions.
Energy modeling has shown that, although it is difficult to match the performance of conventional foam insulation with hemp-based materials, the use of hempcrete in the walls and batting made from hemp bast in ceiling structures, could combine to achieve the levels of performance sought in high-performance buildings.
Gibson’s broader research on net-zero energy housing in the Kansas climate demonstrated that insulation-related heating, ventilation, and air conditioning (HVAC) loads only account for about 20% of energy costs. annually (lighting and appliances contribute 15% and 65%, respectively).
“Thus, in a well-designed net-zero home that uses passive design, load reduction, and efficient building systems, modest changes in insulation level do not have a significant impact on net-zero capacity,” said Gibson. “Hempcrete and hemp insulation could still bring the house within 20% to 30% of a foam insulated house and could result in a successful net zero energy design.”
A group of Gibson seminar students topped hempcrete blocks with concrete for flooring, then looked at R-values, critical indicators that reflect a material’s ability to resist heat transfer by conduction; heating and cooling loads; and thermal pad, in which a mass of material absorbs and releases heat.
Adding a thin top layer of concrete to a hempcrete block floor significantly improved the thermal storage capabilities of the floor assembly, according to computer-modeled results.
The students found six inches of hempcrete with a two-inch layer of concrete providing similar performance to a four-inch concrete slab continuously insulated with R-10 foam. The students found that increasingly thick hempcrete in the flooring increased energy consumption as the interior material moved further and further away from the temperature of the ground.
The experiment also showed that concrete with a high cement content bonded better with hempcrete blocks than a range of other materials tested, including stone aggregates, recycled porcelain and a mixture of corncobs and cement.
Hempcrete blocks in the ground could also be part of a prefabricated solution for zero-energy buildings and other low-energy buildings, Gibson noted.
A second seminar team developed a grid for use as load-bearing structural framing and sheathing for walls that showed performance equivalent to commonly used offset and slip-stud hempcrete framing methods. The grid technique could also be incorporated into prefab construction, Gibson suggested.
Experiments have shown that eight-inch-thick hempcrete walls are easier to build, while being 18% less efficient than 12-inch-thick walls, resulting in only a modest reduction in energy efficiency in a small house.
“Although slip formation and staggered stud walls add complexity to avoid thermal bridging in the frame, the easier-to-build grid wall has a U-value only 6% higher than a wall formed by slippage and only 4% greater than that of a staggered stud wall of similar thickness,” Gibson said, noting that the loss could be overcome by adding a photovoltaic panel to the building’s overall energy infrastructure.
As the seminar continues to explore alternative materials for petrochemical-based foam insulation to prevent condensation in unventilated ceilings and roofs, Gibson recommended that hemp bast fiber padding be preferable to hemp concrete for these parts of a building. Models developed by the students showed that a minimum thickness of 12 inches of hempcrete would be needed in a ceiling to make a net-zero home practical, bringing excess weight.
“Future architects graduating from this class can truly change the face of eco-friendly building and teach the country how to harness and save our natural resources. Construction is one of the many uses of industrial hemp and it has the potential to have a huge impact on our carbon footprint,” said Sarah Stephens, CEO of Midwest Hemp Technology, who attended the UK seminar.
The seminar was attended by Angel Romero Jr., who has experience with stucco and recently started a hempcrete construction business in Dodge City, Kansas.