Trent University has a goal to store more carbon in the building materials of their new Forensics Facility than was emitted in making the materials. In order to offset the inevitable emissions from harvesting and manufacturing materials it is necessary to use biogenic (plant-based) materials that store carbon in the material.

Hemp is the plant-based material of choice for this project. We chose two hemp-based materials for the Trent Forensics facility: Just Biofiber hemp blocks to be the load-bearing walls of the building and NatureFibres hemp batts to insulate the stud wall cavities. This post will focus on the Just Biofiber blocks.

Just Biofiber hempcrete blocks are a new product being manufactured in Alberta, Canada. The blocks consist of a plastic frame around which hempcrete is cast and cured. The blocks look and act much like large Lego blocks, with the eight posts on the top of a block fitting into holes in the bottom of the block above.

The Just Biofiber blocks provide enough load-bearing capacity in the plastic frames to be the structural wall for the building, and offer R-21 of thermal performance. A mortar made from lime and chopped flax is used to seal between each block and glue is applied to the plastic posts to attach the blocks together.

We were excited to work with Just Biofiber hempcrete blocks, having watched the company go through initial development and testing very closely. In practice, we found the system had a few key flaws. Firstly, the glue that is required is smelly, toxic and messy. Our crew truly despised working with the glue. Secondly, the Lego-like fit between the blocks made for a fussy installation as the tolerance is around 1/8-inch and if the foundation isn’t perfectly level a lot of work is required to ensure the blocks actually fit. A lot of dry-stacking is required to ensure a fit, and shimming was constant throughout the process. Finally, there are threaded rods required within the blocks and these were fussy and slow to install. The relatively low thermal performance of the blocks required us to add a frame wall with more insulation to meet our R-40 target.

We loved working with a hempcrete product that didn’t require site mixing or a lengthy drying process, but feel that the Just Biofiber hempcrete blocks need more development before they are a cost-competitive and easy-to-install system. We hope to see Just Biofiber continue to innovate and improve their system and look forward to a chance to work with the product again in an updated form.