HEMP EVENING:��Improving knowledge od sustainable construction�in the Huon Valley…�
DISCLAIMER: Always seek professional assistance to meet your specific project requirements!
The botanical name for industrial hemp is Cannabis sativa L (“sativa” means simply “that which is cultivated” and the “L” refers to Carl Linnaeus who gave this plant its scientific classification).
The cannabis plant has been used by humans for food, fibre, medicine and animal fodder for thousands of years. In the early part of the 19th century hemp was the world’s most widely cultivated crop when demand for sails, cordage and hemp textiles was widespread. The term “canvas” is derived from “cannabis”.
Different varieties of cannabis contain variable amounts of chemical compounds called cannabidiods. One of these compounds is tetrahydrocannabinol (THC) which can have psychoactive effects resulting in the ‘high’ commonly associated with marijuana. Another compound increasingly used for therapeutic purposes is cannabidiol (CBD).
Industrial hemp is defined as a plant that has been specifically bred to have LOW THC levels in the leaves and flowering heads so it has no drug value or effect and can be safely consumed as food. In Australia, industrial hemp is cannabis with less than 1% THC. In other regions like Europe and the USA, the limit is 0.3%.
Q&A:
What is industrial hemp?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
Industrial hemp was spun into fibre over 10,000 years ago and today is grown for an expanding range of industrial and commercial uses. These include:
fabrics, clothing, ropes, shoes, food, paper, bioplastics, insulation, oils, cosmetics, dietary supplements, food products, animal bedding, garden mulch, etc.
The range and volume of these applications are expected to increase, thereby contributing to the growth of the global industrial hemp market while contributing to a sustainable and recyclable economy.
Q&A:
What is industrial hemp used for?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
A. There are projects in France over 40 years old (and getting stronger by the day).
How much industrial hemp is grown in Australia?
Hemp cultivation in Australia peaked at 2,500ha in 2021 with more than half grown in Tasmania. An oversupply of hemp seed and competition from imported products especially from China led to a subsequent reduction in hectares under cultivation.
With a growing interest and investment in processing for fibre and hurd hemp cultivation is expected to increase significantly in coming years.
Q&A:
How long has hemp construction been around?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
Yes! X-Hemp
Are local builders experienced in building with it?
Yes - There are numerous Tasmanian professionals available!
Q&A:
Can Hemp material be sourced in Tasmania?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
Industrial Hemp in Australia for building, mixed with a lime binder which has all the hydrated and hydraulic limes included in it.
How is ‘Hempcrete’ placed and compacted?
Either with temporary forms (GeoPanels) on either side of the structural frame, screwed to the frame at the thickness you are casting or with permanent interior lining board and temporary exterior shuttering (boxing). Tamping the exterior edge of the Hemp/Lime mix will add compaction to the exterior edge of the wall.
Q&A:
What are the materials used to make Hempcrete?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
Typically walls are cast in 600mm lifts but you can do as little or as much as you like, depending on manpower.
*Structural engineer to advise
Do you need to do any testing of materials before starting the job?
NO: you will easily find a rhythm of mixing, casting and tamping with the work crew you have on site and ratios of hemp to binder to water are standard for all applications.
Q&A:
How high can walls be cast at a time?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
Hempcrete cannot be used below ground for foundations. Cellulose exposed to below ground dampness for extended periods will deteriorate, like any plant material, even wrapped in lime.
What precautions do we need to observe when using Hemp/Lime?
Lime is caustic so it’s a good idea to wear gloves when working with Hempcrete. Goggles and dust masks make for a more pleasant experience too. Also, long pants and shirts are and advantage from the dust covering you.
Q&A:
Can we build footings or pad with hemp or do we use concrete?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
There is always spillage when casting Hempcrete but we pick it up and re-use it in subsequent mixes so:
No waste.
What happens to the hemp walls if it rains?
Hempcrete will take on water if rain is beating against it. Depending on climate and time of year you may consider protecting the casting areas with tarp’s. That way you can keep working in inclement weather.
Q&A:
Is there any waste when working with Hemp/Lime?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
Hempcrete provides its own substrate for application of lime plasters directly without need for metal lathing. Or you may wish to use brick, wood or metal facing for aesthetics. Other than wood facings we install a breather baton so the Hempcrete can maintain air flow because metal is not permeable.
Can we use Hempcrete for bathroom walls?
YES! - Yes, you can use Hempcrete in a bathroom and finish with lime or clay plasters that will breathe in and regulate moisture. In Europe people have been using lime materials for ages in bathrooms without the need for extraction fans.
Q&A:
What finishes can we apply over Hemp construction?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
Hempcrete can be used to insulate floors over which you can apply a sub-floor and then whatever flooring material you wish. We prefer to leave a 1″ (25mm) air gap between the floor joists and the subfloor to allow Hempcrete to breathe, thereby giving the best insulation value.
Can the roof be done with hemp/lime?
YES! - Yes, the roof can be done with Hempcrete but remember, as above, there needs to be a ” breathable air space between the top side of the Hempcrete and the underside of the roof sheeting material, presumably plywood.
Q&A:
Can Hempcrete be used for floors?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
Hempcrete is fully compliant with AS 3959, the Australian Standard for Construction in Bushfire-Prone Areas. When used in walls that are 200-300mm thick, with a 10mm lime render, hempcrete achieves a Bushfire Attack Level (BAL) rating of up to BAL 40, making it suitable for regions at high risk of bushfires.
A small hempcrete house built on a block has achieved the highest bushfire rating, BAL-FZ,
(Hempy house - in Blackheath in the Blue Mountains west of Sydney).
Q&A:
What BAL ratings can be achieved?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
Casting into double sided temporary shutters, a 4-5 man crew can form and cast an average 5 cubic meters.
When mixing Hempcrete do you need to vibrate it like concrete?
NO. When mixing Hempcrete and casting you do not need to vibrate like concrete. There is no “slump” in Hempcrete as we limit the amount of water used to hydrate the lime binder.
Q&A:
How big an area can we cast at once?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
There are quite a few variables on cost but it competitive with conventional materials. Hemp/Lime materials are comparable in cost to traditional brick and block construction.
* A Typical Construction Cost 2024:
Typical cost of hemp construction is $135 per vertical m2 of wall construction, this can be compared to:
Concrete wall + insulation $85-100 per vertical m2 (190-240mm thickness),
Blockwork (Besser) $150 per vertical m2 $95-168 (190-240mm thickness).
Q&A:
Do you have a cost per square metre of wall?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
Once mixed, the resulting product is a lightweight, cement-like material weighing around 8x less than concrete.
Currently, ‘Hempcrete’ is not used as a structural element in construction, but used as insulation and infill between the structural framing.
Q&A:
Construction benefits of Hemp:?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
Carbohydrate based building materials are healthier and less damaging to humans.
Toxic petrochemical materials are responsible for many illnesses and increased medical bills.
Hempcrete is breathable and is completely non-toxic due to all natural materials. Plus, Hemp/Lime protects the structural integrity of a home and therefore will last considerably longer than conventional construction.
Are hemp building materials safe/healthy?
Yes: There is documented evidence that Hemp/Lime has contributed to more than 50% reduction in sick leave and absenteeism in Europe where they have been building with Hempcrete for +/- 30 years now
Other sources note anti-microbial properties, resistance to UV, mould, mildew and rot. It can also be beneficial in terms of biodiversity as bees love it.
Q&A:
How is hemp more beneficial in building compared to other materials?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
Because Hempcrete is super insulating the need for additional mechanical heating/cooling is reduced.
For example a typical home will have 1 ton HVAC per 46.45 square metres Using Hemp/Lime for insulation will reduce that requirement to 1 ton per 140m2 (60%) That equates to another cost saving when building with Hemp/Lime.
The HempX video makes mention of the huge benefit in carbon storage over the lifetime of the building,
CO2 is sequestered!
Q&A:
How does hemp help cut down on energy use?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
Hempcrete homes are long lasting. The average home is estimated to last 50-100 years. Hempcrete, on the other hand, has the incredible life span of at least 300-500 years, if not longer… and is recyclable.
Recycling?
Hempcrete is fully recyclable. Any waste on site can be re-used in the next mix. If the building is being demolished, the hempcrete can be easily broken down and used in a new build. As landfill, hempcrete, being a natural product, will break down over the course of time, add lime and organic matter to the soil.
Q&A:
Material Lifespan?
CONCEPT SKETCH BY ANDY ARMSTRONG : ARCHITECT
PLEASE CONSIDER SUPPORTING:�
Please Consider becoming part of the conversation to explore ways to improve the affordability & sustainability of housing in the Huon Valley…
… Ask for a Circular Economy Huon Membership form today, or visit online:
https://www.circulareconomyhuon.org.au