hempcrete - regional appropriateness and best practice

Hempcrete is gaining popularity as a building material, primarily used as an insulation in framed walls. It makes a lot of sense as a local building material, and can be challenging to source if there isn't a local supplier. If you are considering hempcrete we can help with best practice and code alignment, so you have a safe and healthy home.

Basically a simple mixture of hemp hurds and a lime-based binder, a hempcrete mix can be poured and tamped into a wall cavity, fitting around framing and providing a monolithic/continuous insulation in the walls. The walls need a controlled cure/dry that balances the removal of moisture added during mixing with the needs of the lime to get a good 'set'. With a good initial cure/dry, and a properly matched finishing coat of plaster or similar, the walls will act as a vapour-open assembly, managing humidity and indoor air quality while also being highly insulative, anti-fungal/mold/bacteria, and highly fire-resistant. 

Critical considerations:

• Getting a good initial set/dry that isn't too fast (hot/dry conditions that flash cure to a weak set) or too slow (inability to dry, leading to mold).
• Considering wet-weight of hempcrete when initially poured (at ~ 65% moisture content).
• Balancing hempcrete with thermal mass components (slabs, floors, etc) or passive solar design to avoid overheating in summer, and heat loss in winter.
• Moisture detailing and finishing coats to minimize dust and damage.
• Mouse protection so they don't get in the wall and crumble the hempcrete looking for seeds/food.
• Understanding the Effective R-value of hempcrete so as not to overspeed wall thickness.

Here in Canada with our cold climate, hempcrete acts primarily as an insulation. The vapour open properties (primarily due to lime) means it will take in water vapour from the air and store it within the wall - a humidity 'battery'. Humidity control is an extremely valuable property in cold climates. 

Hempcrete thermal mass properties come from humidity stores in the hempcrete itself - a continuously changing moisture content. If the wall has achieved the critical first cure/set, it will excel at moisture storage, and it is this storage of moisture that gives hempcrete its thermal mass properties - keeps homes comfortable and cool in the summer, and comfortable and warm in the winter.

Hempcrete is an excellent option for homes and structures, especially those designed using passive-solar principles, and those looking to be highly energy efficient with a healthy indoor environment. Code approval as an alternate-solution is the most common route, and we can help you by working with your local building authorities to make it happen.

Contact us to discuss our consulting services, and keep an eye on our workshop page for hands-on learning opportunities!