Easy to grow and process, hemp has a number of uses in building, including:
Particleboard/Chipboard
Particleboard based on hemp mixed with other fibers such as flax is lighter, stronger and more moisture resistant than its conventional counterpart. The material in standard chipboard is often held together with formaldehyde-based glues that off-gas over the life of the product. As these glues can’t be used with hemp-based particleboard, it also means a safer product as formaldehyde is a suspected carcinogen.
While it’s not widely available as yet and is more expensive compared to standard chipboard, expect that to change as more companies start manufacturing the product.
The wider use of hemp chipboard could play an important role in forest conservation. While conventional particleboard is often made from wood waste, supply issues have seen trees felled specifically for chipboard materials.
Hempcrete
Hempcrete is a simple mixture of industrial hemp hurds (shivs), a lime-based binder and water.
Hemp hurd/shiv is the inner core of the plant’s stem. The hurd is chopped to lengths of around 6 – 25mm for use in hempcrete. It has a high silica content, enabling good binding properties with lime.
The mix ratio varies application to application, but generally in weight the ratio is 1.5/1.5/1.5 of hurd, binder and water respectively. The ratio will be determined by the final density required.
The dry components are thoroughly mixed together so lime is covering all of the hemp, and then the water is added.
Once prepared, the hempcrete mix is added to the formwork and tamped (packed down). The degree of tamping is also dictated by the density desired. While the formwork can be removed in a few hours, it can take up to a month for the hempcrete to fully dry; depending on wall thickness.
When it dries, it becomes a lightweight but strong building product that can be used in the construction of homes.
Hempcrete offers a number of benefits:
It’s a great insulator
Hempcrete breathes, helping to regulate moisture
It becomes stronger over time
During the curing process, it absorbs carbon dioxide
It’s pest (including termite) and mold resistant
Very low flammability, making it a safe material for homes
An environmentally friendly product
Safe to work with
Fully recyclable
Sound deadening qualities
Less embodied energy in production
Low allergenic
As it’s hygroscopic, maintains a low humidity indoor environment
As mentioned, an advantage of hempcrete is its carbon sequestration attributes. Carbon is locked away in the hemp fiber itself, but hempcrete also continues to sequester carbon long after the building is constructed. This is due to a process whereby the lime-based binder absorbs carbon from the air over a period of time, petrifying the hemp shiv in the process.
One of the disadvantages of hempcrete is that it isn’t load-bearing so it must be used within a framework. The framework needs to be wood as the lime would react with metal. However, the hempcrete helps to protect the wood.
Another significant challenge is in some places industrial hemp is illegal to grow; therefore the material must be imported, which can add to the cost.
When used in construction, the hempcrete is usually cast on-site. While pre-cast hemp bricks and blocks can be sourced, these tend to be denser and don’t have the same degree of thermal and hygroscopic attributes.
As to its durability, a properly constructed hempcrete wall’s life isn’t measured in decades, but instead centuries.
Hemp Insulation
Insulation made from industrial hemp fibers comes in a variety of forms, including batts, rolls and solid panels.
The batts incorporate a small percentage of polypropylene or polyethylene to bind the hemp instead of chemical agents. Hemp batts have a similar R-value of other insulation products of the same thickness.
As in other building applications, hemp insulation doesn’t rot, helps to control moisture and is pest resistant – and is recyclable. Another advantage is in handling – the level of personal protective equipment used when laying down conventional batts is not required; although a mask is recommended to avoid inhaling dust.