Are there any people who do this form of building and/or design?
You will need council approval to build your straw bale home (or any other home). No councils are difficult – some just need more information so they understand this new building material. As there in not an Australian Standards for straw bale building, each building is assessed on its merits. This is called an “alternative solution" where you have to convince the Council that your proposal meets the requirements of the Building Code. A structural engineer with knowledge in current practices in straw bale building is able to provide this information required by your council. One of the goals of AUSBALE is to have the straw bale building technology incorporated into the Building Codes.
What does it take to get buildings designed, approved and built?
The process roughly follows these steps:
- site meeting with architect / designer to view over property
- determine general location of building and any other conditions
- formulation of design brief
- conceptual design
- a contour & detail survey may be necessary for sloping or complex sites
- development of design
- liaison with structural engineer - who can arrange a soil test if required
- construction drawings developed
- applications to shire with engineers certificate
- post-construction / warranty period, etc.
How Affordable is a straw bale house?
A straw bale house may cost the same if not more than the conventional house. Owner built simple structures very little, and there have been homes built for well above $1million. There are many variables that go into building a house such as:
- the size of the building
- the complexity of the site
- the cost of materials, including bales - these vary depending on where you are, but generally about $5-$7 per bale (delivered)
- the type of render (cement is more expensive than earth)
- the cost of labour; the amount of labour donated by the owner and friends
- choice of finishes such as roofing, flooring, and other selections
- your 'waste' treatment/composting system or sewer connection
There are many factors that can make a straw bale house less expensive and there are additional benefits to building with straw. Straw bale homes coupled with passive solar design can be designed in such a way that they do not require artificial heating or cooling. This could translate to a savings of several hundred dollars a year over the life of a home.
How are the walls finished?
The surfaces of straw bales offer an excellent mechanical bond to various types of render. Cement, Lime, Earth and combinations of these are common finishes both inside and outside of the walls. The type of render to use depends on many factors including climate, micro-climate, the design of the building, material and skills availability and cost.
Render can be applied by hand, and this is where owner builders and their friends can really contribute and save. Alternatively, a pump can be hired and the process will take much less time, although cost more.
How do bale walls carry loads?
Both load-bearing and non-load-bearing straw bale houses have been built in Australia, NZ and around the world. Currently most builders use the conventional timber post-and-beam system that carries vertical loads and use the bales as in-fills (this is a non-load-bearing system). Lateral loads, such as wind loads and earthquake loads are carried by means such as diagonal steel straps. Also the rendered straw bale walls act as an additional structural system which makes them more resilient and flexible than the conventional brick/veneer homes. As the saying goes “nature will break what doesn’t bend”.
Load-bearing walls are constructed with pre-compressed straw bales carrying the load of the roof. These homes have special requirements in regards to maximum height, size and locations of openings, etc. Your straw bale builder can advise you of these.
How do you attach things to the walls?
There are many approaches to this. Tapered stakes can be driven into the walls and items can be secured to these. This will hold electrical boxes and typical shelving.
For extra-heavy loads, bolts can be run through the wall to oversized washers on the opposite side. When, for example, securing window and door jambs in openings, wooden dowels can be driven through pre-drilled holes in the wood and perpendicular to the "grain" of the straws.
How do you incorporate plumbing and electrical?
There are many approaches to this. Many builders use the precaution of installing pipes which could sweat or leak inside continuous sleeves within bale walls. Electrical boxes can be screwed to tapered stakes driven flush with the back of recesses cut into the straw, or use surface-mounted boxes. Conduits can be chased into the walls, or skirting ducts are a good option.
Can Workshops and Information sessions help?
Nothing prepares you for building your own home like hands on experience backed with theory which is based on research and current practice. There are several professional groups throughout Australia that are providing this experience for owner builders, professionals, and those who are just looking to be part of an old fashion barn raising. Dates for up coming events can be found on the AUSBALE calendar.
A workshop will give you a sense about the construction process and whether you should take on your own home. It provides a realistic idea of time to construct and render, and the opportunity to ask the questions that you have not thought of yet.
The options then are: to build yourself or employ someone to build it for you. You could employ a builder to do areas such as earthworks, slabs & footings, plumbing, frames, roofing etc; with the walls maybe sub-contracted by owner, or other experienced people who know how to raise straw bale walls.In terms of ease of construction and practicability, building with straw is very forgiving. Those who have attended workshops testify that the process of raising walls is great fun. Preparation for wall finishing and rendering/plastering is the longest part of a wall raising exercise.
Be wary of the friendly soles that have built one and become an instant expert.
Are straw bale buildings more prone to fire?
Rendered straw bales perform better against fire than many conventional building materials. Recent CSIRO bushfire tests (to AS3959) have shown that a rendered straw bale wall can withstand most bushfires. This is because the straw bales are compacted firmly and thus don't hold enough air to permit combustion. Stud construction, in contrast, forms a series of chimneys (stud cavities) which promote combustion.
Also, since plaster applied to the uneven bale surfaces tends to be thicker than normally found on buildings, the bales can be said to carry an extra layer of protection. Nevertheless it is important to apply a coat of render as soon as the walls are in place, as un-rendered bales and loose straw will burn.
Fire tests in Canada & USA suggest that bale walls provide a two hour fire rating, which is higher than timber-framed buildings.
What about Durability?
As with all buildings, durability is obtained through the understanding of the building material, evidence based construction methods, and attention to detailing. The oldest existing straw bale building is in Nebraska, USA. It was built 1903.
What about the pesticides used in farming?
Some concerns have been raised about hay fever, toxins and pesticide residues. When the bales are rendered the irritants (if any) are unlikely to transfer into the building. For the extremely sensitive, there are organic farmers of cereals who bale organic straw.
What are these straw bale buildings like?
Straw buildings have a wonderful quality about them. They appear to have a connection to the earth, which is created by the thick undulating walls with deep recesses. Inside they are quiet, beautifully and comfortable. During construction everybody seems to have a sense or feeling that they are doing something "right". Straw is a by-product of an annually renewable by-product of grains. Locally grown straw has a low embodied energy. You can utilize low skilled labour, bringing people together to work co-operatively and is a great deal of fun. When combined with appropriate passive solar design, these buildings have great thermal capacity which creates stable, comfortable conditions in all climate zones of Australia.
Will pests destroy the straw walls?
Straw is made of cellulose which is not an attractive food source for pests. It is important to distinguish between hay and straw - hay is food; straw is a 'waste' product with little or no nutritional substance. Any animals or insects you get in your straw bale wall will be similar to those you get in your brick veneer home. Straw bales must be rendered on all sides to cocoon them in. Once rendered, any chance of access is eliminated as bales provide fewer spaces for pests than conventional wood framing.
There are few termites who like straw. However, as wood is still used in roofing/doors/windows in straw bale homes, the normal precautions against termite infestation should be followed.
Will the bales rot?
Straw has been found in excellent condition in Egyptian tombs, dated thousands of years old. It has been used as an insulating material for many centuries. This shows that kept in the right environment straw can last indefinitely, just like timber.
Without adequate protection straw bales can rot, like timber. Fungi and mites can live in wet straw, so it's essential to buy bales that have had no exposure to moisture. Bales must be kept dry prior and throughout construction.
To maintain an ideal environment after construction the appropriate render and paint should be selected. These should be “breathable” (i.e. permeable to water vapour) so that moisture doesn't get trapped inside the wall. The design of the building should be appropriate for the local climate, and prevent water concentrating anywhere on the straw bale walls.