So I guess your wondering what sort of house we would live in?
A lot of people would call us greenies. We certainly have a love of the outdoors and are very concerned with the exploitation of our planet. We live in a bushfire prone area so our house had to be able to deal with this and be as sustainable as possible. Our solution was to build a concrete house and bury it – an Earth Covered House!
During the build we had lots of comments about being Hobbits, and that the house would be dark or damp. None of these dire predictions eventuated.
When I say we built it. I actually mean we built it. Pauline and I dug the hole in the ground, set up all the formwork and reinforcing, layed all the blocks, built the retaining walls, did all the landscaping etc….. Well you get the idea. It was a “self build”.
What sort of builders are we?
Neither of us have any formal building qualifications. We have both done renovations on existing houses and flats. Colin has owner built a mud brick house. Our building experience was limited.
Pauline is a social worker. She also has qualifications in aged care and outdoor education. Colin works in IT developing software and doing technical support. In a previous life he worked as a tunneller, so he is familiar with concrete construction techniques.
Why did we do it?
We want to live a sustainable lifestyle… therefore our house needed to be:
- Fire safe – bunker
- Energy efficient & environmentally friendly
- No Maintenance
- Meet our needs as we age
- Close to hiking tracks – the gold field track passes our property and it is only a 25 minute walk into town.
In the beginning
We looked for a suitable block of land. The one we found was North Facing, 5 Deg slope and two dams. It has access to Grid Power. The block needed to be big enough to install a worm composting black & grey water system. It also needed a decent rainfall which unfortunately seems to be deteriorating at an alarming rate!
Who did the design? We did with a little help!
The design process took two years. We borrowed ideas from Frank Lloyd Wright and John Lautner (one of his students). We also used an excellent book – Australian Earth Covered Building.
WE created a 3D model of the house before any formal plans were done. We used this to check solar angles and positioning of the house. We also used the 3D model to actually build from instead of the formal plans.
The floor plan is a classic passive solar layout. Almost all the windows on the North side. There are no windows on the east or west and minimal windows on the south. All the storage areas and bathrooms are on the south.
To ensure maximum natural lighting the windows are 2.8m high. The walls are rendered with white clay (no painting) The concrete floor has white concrete hardener mixed in it to lift the colour and make it more interesting.
The window layout allows for natural through ventilation.
We of course made some changes to the plan before we started. The study was widened. The laundry and store was combined. We moved the refrigerators to the store room as it’s the coolest room. The main bedroom, bathroom and robe was rearranged.
We built the shed first to learn how to use the blocks, build formwork, set up reinforcing and pour concrete. Along the way we realized it would be a huge advantage to do our own earthmoving so we bought our own Bobcat (skid steer loader). This was one of the smartest decisions we made. We still have it and use it regularly.
The shed, like the house was built to minimise the fire risk. It has no timber or combustible materials in it’s construction. The windows and doors are fire rated (BAL40). There are no gaps over 3mm anywhere, this keeps any embers out. All plumbing and services are inside or buried at least 300mm deep.
Home sweet home
Like all real aussie owner builders we lived in the shed for about a year while the build happened. The coldest it got outside was -6 deg C.
The bobcat was put to good use excavating the hole for the house. It created a pile of dirt the size of a large house.
Pauline is spatially challenged so Colin set the chairs in the lounge so she could see what the view would look like.
Drainage is critical for this type of house to succeed. It has to go in first as it’s the lowest part of the entire building.
The rear of the house has a large courtyard that is surrounded by retaining walls. We built these first as it is easier to access them when the house is not in the way.
The house has hydronic floor heating. We had some ridiculous quotes for installing this. How hard could it be? We searched YouTube and found lots of videos on how to do it (and not do it) then installed it ourselves.
The Floor Slab
We had done all of the setup for the floor slab but we needed a lot of help pouring it. It was such a relief to finally be up out of the mud!
We have Walls
The walls are made of 3500 concrete blocks. We layed them all! Pauline has the permanent shoulder injury to prove it! There are of course things that you don’t realize till you have build them, like a concrete lintel above a window. When it’s four meters up the air and you have to set up the formwork and reinforcing and actually get the concrete up there. It helps if you can think laterally.
The roof folly
Of course we had to have our Grand Designs moment. Pauline wanted to get someone to do the roof slab for us. None of the local concreters would look at it. They had no experience with 325mm thick slabs suspended three meters in the air. The companies that specialize in this sort of construction normally do car parks and large blocks of apartments. They weren’t interested, it was too small a job and too far from Melbourne. So we decided to just do it ourselves. We hired all the formwork and erected it ourselves. It took 280 Acrow props to hold up the 200 tons of concrete for the slab. Because we poured it in the middle of winter we couldn’t pull the formwork down for four weeks as the concrete needed to get up to design strength which takes longer when it’s colder. The formwork was costing $2500 per week to hire!
Lock up is a great place to get to. You are finally out of the weather and you can get the feel of the house. It has windows and views and somewhere to store stuff. It’s also about half way in the building process. We still had a long way to go.
Our waste system is a worm farm. It can process all our black and grey water. We can dump all our veggie scraps in it. The only down side is your not allowed to use the worm castings that come out of the worm farm on the garden for health reasons. Nowdays we put the veggie scraps directly in the garden for compost.
It was a very happy day when it was all working. We finally said goodbye to the out side builders toilet. Not much fun in the middle of the night at minus six degrees.
We have two large retaining walls at either end of the house. We decided to build these out of Gabions. It was about half the price of concrete and did not require building the complex formwork required. Because they are so high they require engineers calculations. There is also a lot going on behind the scenes to make them work. There is a complete basket buried under the ground to act as a heel. This stops the wall from slowly moving down the hill. It of course needs a drain under it. So more deep trenches and drains had to be installed.
The Gabions come as a flat pack, so you have to wire them together. Between each Gabion there is a Tensar polypropylene grid that goes back into the soil about four meters that ties it all together. You then have to fill the gabion with rocks and wire the lid on. We used about 270 ton of bluestone for all our Gabions. Each four meter long Gabion took about a day to put together and backfill behind. Luckily for us our friend Ailsa volunteered to help us do this. The height of insanity to volunteer to spend all day bent over stacking rocks! We are most grateful for her help 🙂
Rendering the walls
To avoid painting we had the internal walls rendered with white clay. A local company specializes in this for Straw Bale houses. It took three guys a couple of weeks to do the whole house which saved us months of learning and I doubt we could have done any where near as good as they did. To reduce the amount of material required they did a base coat of clay made from a mixture of our local clay and renderers sand.
Burying the house
The outside of the house is coated with two layers of waterproof membrane. It is a cement/latex/crystal compound that is used on basements for multistory buildings. It can deal with some movement and will self seal small holes and cracks. Painting this on takes ages.
Next is the Polystyrene insulation layer. Followed by a drainage layer which is then covered by a geo fabric. Then you can put on the subsoil and finally some topsoil. There is an enormous amount of work to do all of this even with earthmoving equipment.
Of course by now we were proficient with Bobcat and Gabions so we used them to do most of the landscaping.
What would a concrete house be without a concrete kitchen? In keeping with the “industrial” look of the house it is built with concrete side panels, concrete bench tops and galvanized steel edges.
The solar hot water system uses evacuated tube collectors as we get frosts down to -6 Degrees which can destroy flat plate collectors. The Angle of collector is at 60 Degrees. This maximises the heat collected in winter and minimises boiling in summer.
The storage tank, pump and controller are all inside the house in case of fire.
The system provides all our hot water with no additional energy for 9 months of the year.
Additional Heating and Cooling
We have no air conditioning. During the winter we use a wood fired boiler for heating and for hot water.
The house has three meter high ceilings. To avoid all the heat accumulating up high we used floor heating which gives an even temperature gradient from floor to ceiling.
The house is on the Grid. We have a 3kw system and produce a lot more power than we use.
We have done all we could to minimise the amount of power we consume. LED lights all through the house. Instead of hundreds of down lights we use area lighting with spots for specific functions like reading and the kitchen benches. We bought the most efficient fridge/freezer we could find as this consumes about half our power. The fridge/freezer is also located in the coolest room in the house so it does not have to work hard.
Cabling, Plumbing and Ventilation
All of our cabling and plumbing was installed after the structure was built. We used industrial cable trays routed through the store room, walk in robe and service room. With this setup we can always get to any of it if there is an issue or a change is required.
Because the house is airtight we had to pay particular attention to exhaust fans and ducts. The toilet pans and cisterns are connected to the ventilation system to avoid any smells.
The windows are all double glazed, tilt and turn. All are PVC construction so no maintenance and are a good insulator. The PVC is also self extinguishing, it will char in a fire but will not burn on it’s own. They are also fire rated to BAL40. The windows are all sealed with double rubber seals and kept in place with 10 locking pins. They are completely air tight.
Heating and Cooling
Spring: Average temperature in the house 21 degrees with no additional heating or cooling.
Winter: Last winter we used 10m3 of wood harvested from our property (about $1000 to buy). We keep the temperature above 19 Deg. (-6 Deg lowest outside)
Autumn: Average temperature in the house 21 degees with no additional heating or cooling.
vSummer: Maximum temperature in the house 24 Deg (42 Degrees maximum outside) with no additional cooling. We do not have any air conditioning.
We produce more power than we use. In winter which is the worst month we put 4.3kwh/day into grid and draw 5.12kwh/day. Summer is much better!
We have all the normal appliances a modern house has.
There of course is no end to this project! The garden is under continuous change and all the beautiful trees we have planed continue to grow 🙂