A Passive Solar Hemp Building

By Dionne Payn
Source: HempLifestyleMagazine.com

There are two types of hemp builders. On one side there are your

hemp advocates; those who already know hemp is a fantastic resource

for so many different aspects of our daily lives and would never

consider building with anything else. On the other side, there are

those who set out to build an environmentally responsible home and

quickly realise that hemp is one of the best alternative building

materials available.

 

Kirstie and Ben, who are  currently building their  house on the

Southern New South Wales coast of Australia, definitely fall into

the latter category. "I live in a mud brick house which is

beautiful to live in but building with mud brick is really hard and

heavy work", says Kirstie. Knowing that she wanted to build an

environmentally sustainable home led Kirstie into researching

natural building techniques such as rammed earth, light earth and

straw bale. It was an article in Owner Builder magazine that

alerted Kirstie about the benefits of hemp.

 

Kirstie recalls, "I looked into the light earth technique and saw

cases where the material had taken too long to dry out and the

straw started going mouldy. When I first read about hemp building I

dismissed it as something a bit new and untried, but eventually I

was attracted to it because the lime [used in the binder] is

naturally anti-mould. Plus as the lime dries out it continues to

cure regardless of the weather".

 

During her research Kirstie found that most natural building

materials either provide thermal mass, such as mud brick and rammed

earth or provide excellent insulation such as straw bale. In

contrast, hemp provides great insulation and thermal mass, which

for Kirstie who is building a passive solar house, was an important

factor in her decision. After taking part in a hemp building course

with Klara Marosszeky, Kirstie took the plunge and submitted her

plans to her local Council for approval.

 

Getting Council approval was not a straightforward process to start

off with. Any new build using traditional methods such as brick

veneer and weatherboard must comply with the Building Code of

Australia. As Kirstie was working with a non-standard building

method she needed to prove that it would meet certain requirements

including standards for weather proofing, fire safety and wind

resistance. Once she realised that she needed to find a suitably

qualified engineer who would be able to prove to Council that hemp

building did meet the requirements of the Building Code, and with

Klara's help, she obtained the necessary engineers report and

finally received approval.

 

Building a house that heats and cools itself

 

Kirstie's passive solar design uses the sun and the day/night

temperature to heat and cool the house, without the need for active

sources such as air conditioners and heaters. "I think that every

person who is building a house has an obligation to build the best

way they can. Rather than having a poorly oriented, poorly designed

house that you then have to pump a lot of electricity into to keep

it at a comfortable level, a better solution is to build a house

where the design of the house does these things itself".

 

The house is designed to capture as much winter sun as possible

which falls onto the concrete slab and acts as a thermal mass to

absorb, hold and re-radiate the heat during the cooler evenings. In

summer, the reverse happens; at night all the windows are opened to

let in the cool air, which is absorbed by the concrete slab and

keeps the house cool during the day.

 

The building process has presented some challenges. For example,

Kirstie chose to build using a prefabricated timber frame. "I had

specified stud [the upright pieces of wood in the frame] spacings

of 600mm but because of the location of windows and the extra

height of some of my walls it meant that we had to put in extra

studs. So in some spots we are packing hemp between quite closely

spaced timbers, which is more time consuming". 

 

Another issue Kirstie found tricky is packing the hemp underneath

and around the noggings [the horizontal bracing piece used between

studs to give rigidity to the wall frames of a building]. While

they have figured out a way around this, Kirstie acknowledges that

next time she would work more closely with the framing company

about their designs, as using stronger or larger timbers would

reduce the need for so many of the studs.

 

Hemp building - it's girls work!

 

Having previously built a mud brick shed, Kirstie noted that hemp

building is something that can be easily done by women. "In

contrast to building with mud brick, where after a day of making

the bricks your shoulders and arms know about it, hemp is so light

for its volume. Even when you mix the hemp with the binder and sand

and when you're lifting the hemp and pouring it in, it's really not

heavy work".

 

Another aspect of hemp building that Kirstie found appealing is

that it is not a highly skilled task, which means that friends have

become willing helpers after being shown a couple of times how to

mix the hemp and binder and how to tamp the mix between the

formwork. Kirstie recalls the sense of camaraderie from having

friends involved in the building process. "On a few of the more

difficult sections, we had one person working from the inside and

one person working from the outside. It was just lovely working

together on it".

 

To minimise the environmental impact of the building process,

Kirstie tried to source the hemp and binder as close as possible to

the site. The hemp was supplied by EcoFibre Industries in the

Hunter Valley, about 5 hours away from Kirstie's location. While a

large proportion of the cost was due to transport fees, after

purchasing a semitrailer of hemp there should be enough material

available left over for Kirstie to build her house and either a

garage or shed as well. The binder, which is made and tested in

Australia, was purchased from the Australian Hemp Masonry Company.

 

At just 123 square metres the house is small by today's standards.

However, building a small house is probably one of the best ways to

reduce your carbon footprint as you need less materials and

generate less waste. What about the costs of hemp building compared

to traditional techniques such as brick veneer? Kirstie says "just

based on the cost of materials the price would be similar. The

problem then is that you have to pay a skilled brick layer, unless

you can lay bricks yourself, and then someone to gyprock the inside

of your house.  So the real cost saving for us is that we are doing

the build ourselves".

 

As an owner builder who is also working part-time, Kirstie hopes

that the house will be completed within 12-18 months. Kirstie

advises that anyone interested in learning more about building with

hemp should do a workshop or work on someone else's build to gain

the confidence to build their own house. Kirstie's final piece of

advice to anyone interested in hemp building is "if you are looking

for an environmental building material, that doesn't have high

energy inputs and has a lower carbon footprint, hemp building

definitely ticks all of those boxes".

 

For more details in relation to Kirstie's build visit her blog at

www.culburrahemphouse.blogspot.com.au

 

Resources

 

The Owner Builder Magazine - www.theownerbuilder.com.au

Ecofibre Industries - www.ecofibre.com.au

Australian Hemp Masonry Company - www.hempmasonry.com