Hempcrete — known in French as béton de chanvre — is a bio-composite building material made by mixing the woody inner core of industrial hemp plants (hemp hurd or shiv) with a lime-based binder and water. The resulting mixture is cast around a structural frame, typically timber, to form non-load-bearing insulating walls. It does not function as a structural element and is used alongside conventional framing systems.
Composition and Manufacturing
Hemp shiv is the by-product of hemp fibre processing. The shiv absorbs the lime binder on its surface, and as the lime carbonates over time, it locks carbon dioxide from the atmosphere into the wall. The ratio of shiv to binder affects the final density and thermal properties of the material. Denser mixes have higher thermal mass; lighter mixes provide better insulation per unit thickness.
Several Canadian suppliers distribute pre-mixed hempcrete binder products or hemp shiv sourced from domestic producers, primarily in Manitoba and Ontario where industrial hemp cultivation has expanded since the federal regulatory changes in the 1990s that permitted commercial hemp farming.
- Density: approximately 200–450 kg/m³ depending on mix ratio
- Thermal conductivity: approximately 0.06–0.12 W/m·K
- Vapour permeance: high — the wall breathes and regulates interior humidity
- Carbon sequestration: hemp growth absorbs CO₂; lime carbonation stores additional CO₂ in the wall
- Fire resistance: lime coating reduces combustibility of hemp shiv
Thermal and Hygroscopic Performance
Hempcrete walls do not perform as well as mineral wool or rigid foam insulation in terms of R-value per inch. A 300mm hempcrete wall typically achieves an effective thermal resistance in the range of R-12 to R-18, depending on mix density and moisture content. However, the material's thermal mass provides a buffering effect that can reduce peak heating and cooling loads in climates with significant diurnal temperature variation.
The hygroscopic behaviour of hempcrete — its ability to absorb and release moisture vapour — has attracted attention in the Canadian context, where indoor humidity management during long heating seasons is a common challenge. Published research from institutions including the National Research Council of Canada and European building science programmes has examined moisture transport in hempcrete assemblies, though long-term performance data from Canadian installations remains limited compared to European projects where the material has a longer track record.
Structural Framework Requirements
Because hempcrete is not load-bearing, all structural loads must be carried by the frame — typically light wood framing or heavy timber. The hempcrete is cast in lifts between formwork panels and cures around the frame members. Once cured, it provides lateral bracing to the frame through compression and adhesion, though this contribution is generally not credited in structural calculations under the National Building Code of Canada.
The drying time for cast hempcrete in Canadian conditions can extend to several months, and construction scheduling must account for this. Some builders have moved toward pre-cast hempcrete blocks or panels, which are manufactured under controlled conditions and arrive on site fully cured.
Regulatory Status in Canada
Hempcrete does not have a dedicated section in the National Building Code of Canada (NBC). Projects using hempcrete typically proceed under the alternative solutions pathway in Part 3 or Part 9 of the NBC, which allows materials and methods that are not prescriptively described in the code provided they are demonstrated to meet the intent of the applicable objectives.
Several Canadian municipalities, particularly in Ontario and British Columbia, have seen hempcrete residential projects approved through this route. Approval generally requires submission of technical documentation including material test reports, energy modelling, and vapour management details reviewed by the authority having jurisdiction.
The Canada Green Building Council's LEED rating system can credit hempcrete projects under materials and resources credits related to bio-based content and regional sourcing, provided the supply chain documentation is in order.
Applications in Canadian Projects
Documented hempcrete projects in Canada are predominantly in residential construction: custom homes and renovation projects where owners and designers have chosen to work through the alternative solutions process. Smaller-scale commercial applications have also been reported, including interior partition walls in renovation projects where vapour-open construction is prioritised.
In Quebec, where hemp cultivation has historical roots and where the provincial government has supported agricultural diversification into industrial hemp, hempcrete has been used in rural and semi-rural residential projects. British Columbia's mild coastal climate presents fewer thermal performance challenges but higher humidity loads that hempcrete's vapour-open characteristics can address.
Hempcrete walls in cold-climate builds require careful detailing at the foundation interface, window surrounds, and roof connection to manage thermal bridging through the structural frame elements.
Considerations for Cold Climate Detailing
In heating-dominated climates — which describes most of Canada — wall assembly design must address the condensation risk at the exterior face of the assembly during winter. Hempcrete's vapour-open nature means condensation management relies on continuous drying potential rather than a vapour barrier. This approach aligns with European building science principles but may require additional technical justification when seeking permit approval from authorities more familiar with conventional vapour barrier assemblies.
Exterior cladding over hempcrete is typically a lime render or another breathable finish. Cement-based renders are generally avoided, as they reduce the wall's vapour permeance and can trap moisture. A ventilated rain screen gap between hempcrete and cladding is an alternative used in higher-precipitation zones.