Building An Earthbag Dome House

How do you build social capital at the same time as building your dwelling?

Last week I took my son to a free workshop just around the corner in Kendenup to help build Australia’s first council-approved residential earthbag dome house. It was really fun and the building process was cheap and easy. It took Kate and Scott two years to get council approval, but it’s all systems go now. They’re generously offering to share both their building knowledge and how to work with councils to empower more people to build affordable and sustainable earthbag homes. During June and July 2018, you can learn the earthbag building technique for free in exchange for your labour to put their home together. This is open to anyone who is willing to travel to Kendenup,
Western Australia, and you have the opportunity to camp onsite.

I already have a house to live in, but I would like to add on a greenhouse. And build a walled goddess garden. And I’m just interested in sustainable building methods in general. So I thought I’d go along and see how it all worked. I planned to just attend the morning, but we ended up staying all day. The hardest part of the labour was shoveling dirt into wheelbarrows, and with lots of volunteers there was plenty of hands to help. The bags are filled in place, so there’s very little heavy lifting involved.

When we arrived, the concrete foundations were in place as well as the first two or three layers of earthbag walls and wooden doorway forms. Together with the other vollies, we completed the third layer of earthbags with a layer of waterproofing (this isn’t strictly necessary but ticked a box with the council) and then started on the fourth layer. It’s going to get more interesting when we’re six metres above the ground on the highest dome!

This home has concrete foundations to comply with council regulations, but the traditional footings are a rubble trench surrounding the building. This is Kate’s photo of the foundations of their square test building.

The building process is simple. All the earth for this build is sourced onsite, and screened to remove the largest rocks. After mixing with sand, also sourced onsite, it’s piled up ready for filling bags. The first three layers need to have 30% clay, and also had 5% lime sprinkled into the earth mix, either straight into the bag or as you fill the wheelbarrow. The earth for the rest of the bags is half sand and half gravel.

The bags are bought in bulk and cost about forty cents each new. So the whole house worth was about $1200. For a small build, you could collect secondhand ones as long as they’re about the same size; or I guess you could put the largest bags as the lower layers. Bags are held open using simple frames.

We filled the bags using large tins, working in teams to pass the tins from wheelbarrow to bag and back again. During this stage, the bag being filled sits on a ‘slider’ – a flat piece of metal with one edge bent up for handling. This allows you to reposition the bag until you’re happy with its final placement, so it doesn’t get stuck on the barbed wire.

The house will need a roll or two of barbed wire, at a cost of a few hundred dollars. This is cut into lengths and joined into loops as long as your arm span and laid on top of each course of bags after tamping. Standing on the barbed wire stops it from flicking around while you’re twisting the loop closed. Then bricks hold the wire down on top of the backs until the next row of bags are laid. The wire grips like Velcro and stops the bags from sliding. The course above had the extra layer of black waterproofing under the wire.

After four tins full of earth, the bottom corners of the bag are tucked in. This keeps the walls flatter for smooth rendering later. If you forget to do this step, you can poke the bag corners in with a pair of pliers or something, but it’s much easier to do when the bag is less than a quarter full! We wore gloves whilst handling the lime and earth mixture, but this isn’t necessary once it’s just earth. Although gloves are a good idea if you’re handling the barbed wire.

When the bag is full, after about 22 tins of earth, unhook the bag from the frame and jiggle it to settle so it doesn’t tilt until you’re ready. Then lift the frame off. Tuck the top of the bag over like a gift, eye the distance to the next bag and adjust the position of the bag if necessary, then push the bag down neatly. It’s hard to make adjustments once it’s down and jagged on the wire, but you can hoist it back up again with some help and try again if it’s really wonky. Then pull the slider out and work on the next one.

All bag ends should be facing another bag, so bags butting against a door or window will need to be turned around. In this build, plywood forms marked the door spaces. Wooden bits were laid where the hinges will need to be, so there’s something to drill into.

You can also lay shelf supports as you go, to be firmly embedded into the wall. Once it’s finished, just lay the shelf on top. This house will have a huge pantry with lots of shelving. Above are Kate’s pics of shelf supports and a sink in their test build, a square bathroom block, which is now roofed and rendered.

Like bricks, each row of bags should be staggered for structural integrity. If the joins start to line up, make a half bag. Bags right at the end of a wall (like on this buttress) will tend to bulge out if they are only tamped after laying, so end bags should be tamped with a small tamper when one quarter full as well as after laying. That helps to firm the ends up.

After laying each course, the bags need tamping down to settle the soil. We used several homemade tampers of various weights. Lighter ones are easier for people with smaller arm muscles. The wall should be tamped thoroughly until it is level before laying the next course.

To quickly measure the level evenly around the circle, a central pole can be set up with a swinging arm that contains a spirit level.

If there’s a low spot, mark it before laying the next level so you remember to fill the bags a bit extra above it. High spots can be tamped down extra hard. Filling the bags about the same volume every time will reduce the likelihood of uneven wall heights, but this building method is pretty forgiving.

And then you do the next layer! To make a dome, each layer creeps inward by a centimetre. I’ve only laid one layer like this so far, below (not yet tamped). After the dome is complete, the building will be rendered. So the bags don’t have to stand up to UV rays and weather in the long term.

I wasn’t sure about the idea of encasing the earth in what is essentially plastic bags, when it is possible to build rammed earth or cob without plastic. However, the accessibility of this method definitely makes it a viable option to consider. The bags basically provide a very thin internal framework, instead of the sturdy temporary external framework needed for rammed earth. It’s easy to source and set up. And they give a consistent and reliable build, with less variability than using unencased earth like cob.

The end product is cheap, provides excellent insulation from temperature variation, is sturdy and long-lasting, and, importantly for Australian conditions, is a safe refuge in a bushfire situation because the walls are thick and strong. You can build either straight walls or curved, and it’s easy to customise as you go.

I’m looking forward to going back for more, as further techniques will be demonstrated at different building stages. I’m especially interested in learning how to make tadelakt, a traditional Moroccan waterproof plastering technique that you can use to create free-form baths and sinks. The walls will be rising each week, and there will be window framings and dome-building and rendering. It’s going to be awesome.

This way of building a home is a real community effort. The couple building this house will own their home and land in a few years, rather than being stuck servicing a mortgage for three decades. Plus it will be a unique and interesting home that’s a peaceful and harmonious space to be in, not a white box. And it will contain the memories of all the people who contributed and learnt and shared and grew connections together. Rather than exploiting free labour, it’s an empowering two-way street of time and skills exchange, local knowledge transfer and storing up goodwill with friends new and old. You can’t buy that.