a building material which is self-insulating, soundproof, non-toxic, pest-resistant, fire-resistant, & mould-resistant; resulting in homes which are constant-humidity, ultra-durable, don’t need much in the way of heating or cooling, aren’t damp, won’t rot, are ecologically sustainable with an extremely low environmental impact, & absorb carbon dioxide both before & after construction.
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Hemp lime has been under development since the early 1990s, mainly through work in France & Belgium, but also including research work in the UK. Hemp-lime construction is a composite construction material & building method that combines fast growing renewable & carbon sequestrating plant-based aggregates (hemp shiv) with a lime-based binder to form a lightweight material that is suited to solid walls, roof insulation & under-floor insulation & as part of timber-framed building.
Normal practice is to construct a simple timber frame or sub-frame which provides the principal structure of the building supporting any floors & roofs, the hemp lime is then sprayed or cast around the timber frame to provide solid walls, & possibly floors & roof.
This creates a composite structure that is very strong. This form of walling is also a breathing wall, allowing the passage of moisture vapour.
The hemp is able to absorb quite high quantities of water & then release it again without damage. It is normal to render the outside of a hemp wall with a lime plaster to keep the rain off.
The composite provides a reasonably good level of thermal insulation with the added advantage of retaining warmth due to its thermal mass. There are very few materials which are both an insulant & able to retain warmth.
This makes the material especially good for climates where there is a high level of humidity.
The lime in the mixture helps to preserve the timber frame & the hemp lime mixture sticks to the wood very well. The lime protects the shiv from biological decay, mainly through its ability to wick water away from the hemp shiv & its high alkalinity, as well as providing essential fire resistance.
A particular benefit of hemp lime construction is its capacity to sequester carbon dioxide into the building fabric. As government policy becomes increasingly concerned with reducing carbon emissions & finding more efficient ways of meeting current targets, it seems possible that hemp lime can make a major contribution to this offering a genuinely zero-carbon solution to sustainable construction. (Woolley 2004,2009)
Another important property of hempcrete observed from compression tests is the large deformation it can undergo after reaching the ultimate load.
This shows hempcrete has a quasi-ductile behavior unlike the sudden brittle failure associated with concrete. (Mukherjee 2012)
On a four hectare lifestyle block a few minutes north of New Plymouth, New Zealand’s first hemp house is being built.
Amongst wandering sheep, chooks & bee hives, the house is being constructed out of timber & hempcrete – a mixture of hemp, lime & water.
The hempcrete comes from company Hemp Technologies, which was founded by Taranaki-born man Greg Flavall in the US state of North Carolina. In about 2008 Flavall, who had worked as a builder, came across hempcrete, which he says has been successfully used in construction in Europe for about 30 years.
He took it back to the US & from there, he took it all over the world. In 2010 Hemp Technologies’ hempcrete was used to build the first Hemp House in the US, in Asheville, North Carolina.
The business has branches in New Zealand, the US, Canada & Romania & Flavall says it employs about 300 staff, from admin & distribution to chemical scientists.
Today the company has projects in the US, Mexico, South America, Canada, Australia & right here in New Zealand. Flavall says he has 24 building projects on the go here at the moment.
He has four Hemp houses in the pipeline in New Plymouth. Two have been pre-sold. Hemp Technologies & Venture Taranaki are working on crop trials with Massey University, & in February , Lincoln University’s Agribusiness & Economics Research Unit penned a Venture Taranaki funded report that identified hemp as a crop that would enable diversification in a region dominated by dairy farming.
The report, which was presented by senior research officer Dr Glen Greer, said hemp had been used for many centuries as a building material & was “light, hypo-allergenic & had the highest insulation & noise-reducing properties of any cellulosic product.” (Taranaki Daily News 2014.03.17)