Hempcrete – a whole (not so) new low energy material

Everything old is new again. We are so often returning to new interpretations of traditional low-tech ideas in our search for a path forwards. Hempcrete is just such a material, and now sits squarely on the palette of materials available to us for low energy building materials. It’s not new (the oldest existing example being 300 years old), it can be square but also any shape you like (free up your imagination!), and it is definitely a great way forward (sequesters carbon). So what is it?

The industrial hemp plant has a tough woody stem, which is chopped up into short pieces of various sizes called ‘hurd’, and when combined with a simple lime binder, undergoes a pozzolanic reaction, effectively petrifying, or turning to concrete. The full cure time is several months, but it sets in hours, allowing building work to proceed quickly.

What are the advantages of the material, from seed in the ground, through construction, operation, and deconstruction?

Agriculture:

• fast growing cycle
• no irrigation required
• no pesticide required
• no fertiliser required
• low capital investment for the farmer
• government regulators license planting, but you can’t smoke industrial hemp, it’s a different species to ‘weed’

Design:

• carbon negative/sequestration…
• In 1 cubic metre mix of hempcrete, emitted CO2 is:
  • 110kg of hemp hurd = – 202 kg (CO2 absorbed)
  • 220 kg of lime binder = +94 kg (CO2 released)
  • Total sequestration = -108 kg/m3 of wall built
• thermally efficient – good R value/thickness, eg 250mm thick wall provides R2.8~3.5 depending upon the density selected
• moisture & humidity control is extremely high – solves problems of non-breathable buildings, and this is increasingly important!
• flexible – can be adapted to virtually any shape or detail: crisp/rectilinear or soft/curved

Construction:

• Codemark certified under the National Construction Code (previously the BCA)
• can be formed in situ
• can be precast or in blocks (not yet in Australia, but people are working on it)
• flexible – can be built in short sections or in long lengths, helping site management
• skills easily learnt – no need for a specialist team of highly skilled trades

Deconstruction:

• easily deconstructed – no need for noisy jackhammers
• recyclable – can be used again as aggregate in other mixes, or will compost as fill

Training – we are working with leading hempcrete suppliers and Building Designers Australia to bring a hands-on real building design and construction workshop to Sydney in the first half of 2013.  Stay tuned.

More information can be found on these websites:

Hempcrete Australia

Australian Hemp Masonry Company

Hemp Gallery