The Hemp Building Association (HBANZ) says that hempcrete is a bio-composite construction material used for walling. It can be used for residential and commercial builds. It can be hand-placed ‘in situ’ using temporary shuttering/formwork. It can also be made into panel systems / blocks and can be sprayed.

“Hempcrete is comprised of hemp hurds (the dried processed inner part of the hemp plant stalk) a binder, and water. The hempcrete binder has been mostly a lime-based product,” says Jo Say, co-founder of HBANZ.

She says that although the word ‘crete’ is part of its name there is no concrete in hempcrete.

“The hemp hurd processed product (from New Zealand grown industrial hemp) is now easily available from a Christchurch production facility and is being delivered to builders all around the country including to the north island. ”Say explains that the benefits of hempcrete are numerous.

“Hempcrete sequesters (absorbs) significant amounts of carbon dioxide while growing and continuing when combined with its binder. This means every hempcrete building is a carbon sink, removing tonnes of carbon from the atmosphere rather than generating tons of carbon. Hempcrete is then one of the few carbon-negative construction materials available to us. Even with the lime in most hempcrete binders, it can contribute to a building being carbon zero or carbon negative.

”A second benefit is its naturally high insulation R-value, coupled together with its strong thermal mass performance. These two thermal elements work dynamically together to produce a stable temperature inside hempcrete buildings. A hempcrete house can easily offer a passive house thermal performance. The heating and cooling of a hempcrete-built building (and any associated carbon burden) is minimal.

“A third significant benefit is that hempcrete has a natural capacity to self-regulate moisture – it has a good hygroscopic performance.” When humidity levels rise inside a home the hempcrete walls can absorb that moisture and then release it back when the internal humidity level has dropped. This has a very positive impact on negating the possibility of mould and condensation. Hempcrete walls are literally breathing.

“There is minimal landfill waste during the hempcrete build – almost zero – which is a significant fact given that half of Aotearoa’s landfill waste is from the construction industry.” She adds that no plasterboard or other lining sheet is used to line the building. Instead, it is plastered with a clay or lime plaster or it can be just coated with a breathable water glass silica sealant to enable the product’s natural finish to be seen. Framing can be from untreated timber as the lime in the binder works as a preservative.

On the exterior face of hempcrete walling the hempcrete is sealed and made watertight with a lime and natural sealant system

Additional benefits are that hempcrete is totally non-flammable; it can be used to retro-clad existing houses; and it has great acoustic and seismic performance.“

It can be used by LBPs, or owner builders. In the future it will be installed by a hempcrete contractor. This latter option is a strong business opportunity waiting to be snapped up by someone. If you’d like to know more – feel free to ring me to discuss.”

The eight hempcrete homes built here in New Zealand have used an imported binder, either from Australia (from the Australian Hemp Masonry Company) or a European product ‘Tradical’ – from Europe but imported via Australia.

“As a construction walling product which can be part of the solution for reducing carbon emissions in the construction industry, importing a hempcrete binder from Australia was not ideal. But none was produced locally.”

But that’s all changing she says. Kerikeri building firm Rockstead Construction is currently bringing to market Geobind – a blended mineral based geopolymer binder, that when mixed with hemp hurd as a bio aggregate, creates carbon neutral hempcrete.“Geobind may well end up being one of the best performing hempcrete binders in the world. Rigorous testing through Callaghan Innovation has confirmed that when mixed with hemp hurd, Geobind excels in both strength and durability when compared to similar products.”

Geobind is already available for hand placed application. Further R&D is currently underway to develop Geobind value-added products such as bricks, blocks and panels.“New Zealand is trailing behind Australia, Europe and America with its use of hempcrete in construction. Limited knowledge about hempcrete construction here in Aotearoa is one of the reasons we have only eight completed hempcrete homes. All of these completed hempcrete homes have received their final Certificates of Code of Compliance from various regional building authorities.

”In America recently, the International Code Council (ICC) approved Hempcrete for the USA International Residential (Building) Code.