28 THE OWNER BUILDER � 198 December 2016/January 2017 � © www.theownerbuilder.com.au

From conceptionto lock-up

Sustainable retirement straw bale and mud brick home at Mudgee

resources and producing many tonnes of greenhouse gases is simply to use an existing house. However, there was no existing dwelling of any sort on our block.

Perhaps the biggest problem faced by people wishing to build sustainably is the lack of any holistic defi nition of what constitutes a sustainable house. One guide is the Brundtland defi nition, ‘Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.’ (Gro Harlem Brundtland was the former Prime Minister of Norway. She was appointed to head the United Nations World Commission on Environment and Development (WCED). The report of the commission, ‘Our Common Future,’ also

known as the Brundtland Report, was released in October 1987. It contained the quoted defi nition, which coined, and defi ned the meaning of the term ‘Sustainable Development’).

But how does this translate into decisions about home design, material choices, embodied energy, etc., etc., etc.? At a practical level the Brundtland defi nition provides no guidance. However, the principal underlying idea is intergenerational equity. To respect the rights of future generations, sustainable development should avoid creating greenhouse gas emissions and should avoid consumption of non-renewable, non-recyclable materials.

We decided to adopt this following defi nition of sustainable development for our project: A sustainable residential

development is one that generates zero

net greenhouse gas emissions from

construction and ongoing occupation.

Around 10 years ago my wife Rosemary and I decided to escape Sydney and its evergrowing urban density, traffi c and pollution for a more relaxed country life in our retirement.

We have been avid permaculturists for around the same length of time so a big part of our plan was to develop a property according to permaculture principles and design concepts. We wanted to minimise our impact on the environment and live more sustainable lives.

After some searching we found our dream block of 10 hectares, 10 kilometres north of Mudgee in the NSW Central Tablelands.

What defi nes a sustainable home?

How does building a house fi t into this equation? One solution to the dilemma of achieving a roof over your head without consuming a large amount of

BY BARRY HADAWAY

we incorporated a ‘cool cupboard’ for storage of fresh fruit and vegetables into the house design. A fan will draw air through two deeply buried 25 metre long pipes into the bottom of the cupboard.

• To install a solar hot water system that works effectively at low pressure.

• To use gravity for water reticulation to the house, from a header tank, and around the property, from a high dam, to avoid the need for pressure pumps.

• To install a wood burning stove with a wetback providing a boost to our hot water system in winter. The wood burning stove will only use wood we grow ourselves on our own property.

• To install a wood burning slow combustion heater, which will also use only wood we grow on our own property so we will have a closed loop system and zero net greenhouse gas emissions from cooking and heating.

• Plant trees to offset any unavoidable greenhouse gas emissions from our concrete slab fl oor and corrugated steel roof.

• To use materials that sequester carbon such as timber, straw and our external lime render.

Design ideas

We spent a number of years playing with different design ideas. We wanted to build sustainably but were unsure of the best approach for us. We considered reverse brick veneer with mud bricks internally and we considered straw bale. To learn more about straw bale building,

Sustainable criteria

Our strategy for building our home, in accordance with this defi nition, was to:• Use natural building materials as

much as possible, such as, straw, clay, mud (for mud bricks), sand and plantation timber.

• Source materials locally where possible. We made mud bricks ourselves from soil from our own block. We dug clay from our block and after much crushing, wetting, stirring and sieving used it for the internal render over our straw bales.

• Adopt solar passive design principles so our house would need a minimum of energy for heating and none for cooling. We chose a building site on the midpoint of a north facing slope for best thermal advantage.

• To ensure our electricity needs were modest and to install an off-grid solar power system. To reduce energy needs

Above: House at lock up stage enjoys the sunshine on the north facing slope.Opposite page L–R: Lifting hardwood ring beam segment; unloading rice straw bales; curved window reveals after clay rendering.

THE OWNER BUILDER � 198 December 2016/January 2017 � © www.theownerbuilder.com.au 29

30 THE OWNER BUILDER � 198 December 2016/January 2017 � © www.theownerbuilder.com.au

I attended a straw bale building course at the Australian Rural Education Centre at Mudgee. This course gave me confi dence that straw bale was something doable by an owner builder.

We decided to build our external walls in straw bale and to build one large mud brick internal wall down the spine of the building for thermal mass. This wall separates the kitchen, living/dining and library/offi ce spaces on the northern side of the building from bedrooms and utility areas on the southern side.

Apart from following solar passive design principles, the layout of the house and aesthetic touches are based largely on ideas contained in a wonderful book by Christopher Alexander et al. called A Pattern Language (ISBN 9780195019193). We also received valuable suggestions and help from friend and architect, Graeme Scott.

The area of the slab is 186m2. The internal fl oor area is approximately 160m2 due to the thickness of the straw bale walls and the central mud brick wall.

Changing our minds

We started to build in 2013 before we moved from Sydney. A waffl e pod slab was poured in February 2013. We opted for a waffl e pod design to reduce the amount of concrete required and to provide sub-fl oor insulation. The big move from Sydney was in May 2013 and we spent some time making our temporary quarters, 'the shed,’ more liveable before starting to make mud bricks. We made around 2200 bricks before doing something home builders shouldn’t do – we changed our minds!

The original plan was to build the mud brick wall as a structural wall 4.2 metres high and 16.9 metres long. I got cold feet about the prospects of building such a large structure in any reasonable length of time and keeping it dry. Instead we decided to make the mud brick wall an infi ll wall and to reduce its height to three metres. This required consulting an engineer to design a post and beam

This page from top: Temporary rafter fi xing; straw bale workshop participants splitting bales; making mud bricks from on site soil.Opposite page: Fixing wire around trench mesh corner braces in bale walls.

THE OWNER BUILDER � 198 December 2016/January 2017 � © www.theownerbuilder.com.au 31

structure to support the roof. This change meant we could put the roof on fi rst and build the mud brick wall under cover.

The framing of our house is fairly simple. There are laminated veneer lumber (LVL) uprights around the perimeter. The straw bales sit between these uprights, which are tied together at the top by a hardwood ‘ring beam’ running around the full perimeter of the house. The LVLs also double as window boxes. The hardwood ring beam carries the roof trusses and rafters.

Rosemary and I installed all of the LVLs, the ring beam and with help from a local builder, Dean Reinberger, I stood the internal wall frames. The heavy pieces of hardwood for the ring beam were loaded onto the back of our ute using a ute crane and then hoisted into position using pulleys and ropes fi xed to temporary steel angle irons bolted to the top of the LVLs.

We have used the services of a private certifi er, Peter Whitehall. Peter was referred to us by a permaculture friend who told us, ‘He’s okay with weird stuff!’ Peter has been accepting of our choices of natural materials and, I believe, feels the house is, if anything, over-engineered.

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32 THE OWNER BUILDER � 198 December 2016/January 2017 � © www.theownerbuilder.com.au

Straw bale work

Justin Penney, one of Mudgee’s respected builders, constructed our roof and then we were ready to tackle straw bale building. Rosemary and I worked on a couple of straw bale builds to gain experience. We were greatly impressed by the passion and work ethic of volunteers so it was automatic for us to choose to run workshops for our own wall raising and rendering.

We purchased rice straw bales because of their high silica content and started to search for a straw bale builder to help us run our workshops. We were fortunate to fi nd Pete Sim from Reliable Constructions, whose own straw bale home features in TOB 178 August/September 2013.

Our straw bale workshop was attended by 15 volunteers. Together with Pete Sim and his two men plus Rosemary and I we had a total of 20 willing workers. The

installation of all bales was completed during the three-day workshop with time left over for a rendering demonstration.

Render rules

A few weeks later we held a rendering workshop to cob holes, to start shaping window and door curves and to apply the fi rst coat of render. We used a lime render on the outside of the building and opted to use our own clay for a clay and sand render inside. The clay was mixed to a thick slurry and sieved to remove any stones, with the clay for the fi nal coat being pushed through fl y wire. Our windows and doors were installed before the fi nal coat of render was applied.

One thing we learnt the hard way was how long it takes a clay render to dry in the middle of a Mudgee winter when temperatures dropped as low as minus 5 degrees! However, Pete Sim and his team persevered and produced a great result.

The completion of the rendering meant we were fi nally at ‘lock-up’ stage. Someone told me the build is half completed when you reach lock-up! I didn’t believe it then but I do now.

How have we fared in achieving our aim of producing zero net greenhouse gas emissions? Our calculation of greenhouse gas emissions for the big ticket items – the concrete slab, steel roof plus fi xings, lime and a small amount of cement in the external render – came to a total of 21.8 tonnes of CO2. The total weight of CO2 sequestered is approximately 28.2 tonnes. Most of this is contained in the timber and rice straw bales and small amounts are sequestered by our wheat straw Solomit ceiling panels and by the lime render as it calcifi es.

However, every item in the fi nal fi t-out; taps, light fi ttings, white goods, etc., contains some embodied energy so we will be lucky to break even. As we implement our permaculture plan for our property we will be planting many trees so we can be certain we are making a positive contribution towards reducing greenhouse gases and meeting our defi nition of sustainable development. �

� Trent Gardiner

Supplier of rice straw building bales.02 6954 6121, www.straw.com.au

� Penney Constructions

Mudgee building / rammed earth specialist.0428 213 963www.penneyconstructions.com.au

� Pete Sim

Straw bale construction and rendering. Renovations.

0419 424 316www.strawbalehomes.com.au

� Whitehall Building Certifi ers

0402 697 442

� Graeme Scott

Architect, Senscott Pty Ltd02 9802 8088

Links & resources

Above: Laying mud bricks on internal wall.Below L–R: Sieving clay for internal bale wall fi nal render coat; mixing water and clay.