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Sustainable House: it behaves “like a tree”

It’s a home so self-sufficient it processes its own sewage, but it’s no wacky experiment in living, rather a very normal-looking urban house. Its creator gave us a tour and explained the bright future of vertical gardens and carbon farming soil.

Back in 1996, before terms like greywater and rainwater capture were part of the mainstream lexicon, Sydney environmental lawyer Michael Mobbs decided to transform his home into a power, water and sewage plant capable of providing for his family.

This was not to be a rural experiment. Mobbs and his wife and two children didn’t want their home to appear, or smell, “freakish” nor did they have a large estate on which to conduct experiments; they live in one of Sydney’s most densely-populated suburbs (Chippendale) on a 130 square meter site (1400 square feet).

After installing solar panels, smart gutters, an underground rainwater capture tank and a mini-wetland, Mobbs was able to take the home off the grid. Today, the house:

  • Collects all of its drinking water from the roof.
  • Captures all of its electricity from the sun.
  • Processes all of its wastewater and sewage.

Annually, they now save:

  • 102,000 liters of water and 4.3 tonnes of coal from burning.
  • More than 60,000 liters of sewage from entering the Pacific Ocean.
  • More than 100,000 litres of clean water is produced.
  • More than 80,000 litres of stormwater is kept out of Sydney Harbour.
  • Carbon dioxide pollution from power stations is reduced by 8.3 tonnes, reducing greenhouse pollution.

We stopped in at the Chippendale (Sydney) home for a tour of the water and electric systems, as well as a peak at Michael’s newer projects: vertical gardens and chicken coops.

Living like a tree (that can’t shop for food, energy or water)

Michael Mobbs: “In 1996 we were doing a kitchen and bathroom renovation and we decided to make all our energy and water from the roof so basically we wanted to live like a tree, which can’t go shopping for food, energy or water.”

“The house is not connected to main’s water sewerage which is right in the heart of Sydney so we stop 4 tons of coal being burned a year; we stop 8 tons of green house gases going up; we leave over 100,000 liters of water in the river for the fish and the farmers and we stop over 100,000 liters of sewerage going to the ocean.”

It’s just an ordinary house. I did this kitchen and bathroom renovation in 3 months and in doing that we put in the rainwater tank, the sewerage and the energy system so we have a bigger kitchen and bathroom, but we’re using less energy and water basically because everything is efficient.”

“For example, it’s about 11 o’clock, but there are no lights on because the stainless steel bench, the louvers, and the light ceilings reflect all the light in so for most of the day, for most of the year we don’t have to turn the lights on just by using things that are free. When we do turn the lights on all of this light is coming from the sun.”

“Tonight when I turn the switches on it will come from the main power system and today while the sun is shining I’m making more energy than I need. I’m exporting it back to the grid using the power lines in those boxes I showed you at the front.”

“Such an ordinary house! You can walk in here and say ‘Is this really the house!’ which I think is an achievement. It shows you that you don’t need to change your lifestyle, or be different, or be special, or be skilled.”

“Why did I do this? I had been a lawyer for 20 years doing environmental law and the more laws there were the more pollution there was and it didn’t make sense to me. So when we renovated our kitchen and bathroom I decided to do these things, at least to control my own pollution.

It was more or less a childish response to being told by engineers, architects, planners and city builders that it couldn’t be done. I think the thing that has really inspired people is just how ordinary the house is.”

Drinking water from the roof: a 30 dollar gadget to clean water

(Mobbs offers us a glass of water).

“This water here from my tap is off my roof, but this water is cleaner than main’s water and there’s data showing it’s cleaner than main’s water.”

(He steps outside to show us his Smartflo guttering system).

“Up here is an ordinary looking gutter, but it’s actually a self cleaning gutter. When the sun shines and the pollution is coming down the wind blows the pollution down and over.”

“When the rain comes down into these intake points and if it’s raining really hard the water plumbs in here and the plumbed water acts as a brake and stops the water from flooding so this is really more efficient at gathering rain water than the ordinary open gutters.”

“When it first starts to rain there’s still some pollution on the roof and the solar panels and that first dirty water comes down to these dead end gutters. As the water comes down, dirty water floats the ball up to this T section where an internal lip stops the ball going any further.”

“By the time the first dirty water has raised the ball to this point the roof has been washed clean and the ball diverts the following water which is now clean down here into my tank. There’s lots of dirt and gunk on this thing here, but the water that I poured into my glass has come straight from the tank. So the water going into the tank is clean.”

“I don’t need to filter it which reduces the energy and the maintenance. This thing is thirty odd dollars and it’s self cleaning, using the energy of the water. There’s a hole here to drip away the dirty water and I don’t have to do a thing. And we know the water’s clean because we’ve been testing it and testing it.”

“So it’s very empowering; $30 and you don’t have to think about cleaning your gutters; it uses the energy of the water to clean the water.”

A rainwater tank for a family of 4

Michael shows us how the water then goes to a concrete tank buried below the deck. His rainwater capture tank has a capacity to hold 8500 liters of water (they’ve only run out of drinking water 4 times in the past 12 years). They use this water for drinking, cooking, showers, baths and hot water.

When it rains a lot and the tank is full, any excess water flows into a small wetland to help minimise runoff from the property.

“When this rain tank overflows it comes into this pond which has frogs and taddies. That’s where the water is kept, out of the sun because it’s such a hot country and we want to make sure that there’s always water here.”

Worms and bugs eat the sewage

Water for toilets, washing and irrigation comes from another tank that is part of their wastewater treatment/recycling system. This tank contains three layers of aerobic filter beds of sand and peat where earthworms and microorganisms break down the human effluent, greywater from the washes, showers and sinks and food scraps.

The water leaving the treatment tank is further disinfected by an Ultra Violet (UV) light disinfector to ensure that it’s sterile. At this point, the water is probably clean enough to drink, but it isn’t used for drinking. Instead, Michael and his family use it to wash clothes, flush the toilet and water plants. Any solid matter leaving this waste system is disposed of in a dry reed bed.

(Michael points to the wastewater treatment tank).

“Over here is another tank about as wide as this table. You can probably hear a bubbling noise; it’s air being blown into that sewerage. The air cleans it; it takes away the odor and the color and it creates an environment where bugs can live and eat all the suspended matter. And then the water is pumped back. When I flush the toilet, wash the clothes or hose the garden the water is my recycled sewerage.”

“The average Sydney person uses 274 liters of water a day. Here 4 people use 230 liters, not because we don’t wash, but because when we flush the toilet and wash the clothes we’re reusing sewerage. In this dry country the only way we can sustain ourselves with water is to reuse water. It doesn’t matter if it is main town water, sea water, or rain water; unless we reuse our sewerage we’ll never be able to meet all our water needs.”

“It’s a small back yard, 5 meters wide 8 meters deep. The reason I can reuse my surplus sewerage is because there is not much of it. The 230 liters of water that 4 people use a day is added to the tank and is surplus each day so it’s that surplus water that is absorbed in the small garden. So no sewerage has left here in 11 years.”

Solar and the importance of the fridge

(Michael points to the solar panels on his roof. There are 18 photovoltaic panels producing approximately 2555 kWh -kilowatts hour- of electricity).

“The solar panels do two things: if you look at my hand you can see the sun striking it. When you put a solar panel over a house you’re actually giving it another roof and it cools the house. So as well as making solar energy you get the cooling effect of the solar panels.”

“The biggest mistake I made was my refrigerator. The house was using 24 kilowatts of energy a day and after the renovation it was using 6 and the fridge was using 4 kilowatts. The fridge was using 14 of my 18 solar panels; it was a gas guzzler. It was a very inefficient fridge, but I put it in a space where it wasn’t properly ventilated.”

“Just by improving the ventilation of the fridge I could have halved the amount of energy I used and made my solar panels more efficient. By ventilating I mean getting fairly cool air to come up from below the fridge pass the fridge and could have improved the efficiency up to 25%. It was really hard to bring the cold air over that side.”

“The fridge uses most of the energy in the kitchen. It’s important to keep it away from the ovens and the dishwasher. The hot air made by the fridge goes up and it goes nowhere. Wouldn’t you know that the new towel racks in the new bathroom are directly above and I could have taken the waste heater up and dried the towels for free. All the connections in a building are not often acknowledged during this process. But now I understand. The fridge is the most important thing in an Australian household to get right.”

Growing soil and the importance of a proven sewage system

faircompanies: It’s been nearly 12 years since your sustainable remodel, I’m sure technology has changed in that time. What would you do differently?

“If I was to do this again the main thing that I would do differently would be the sewerage system. I got a new system and with sewage you’ve got to use systems that have been proven; it’s really important not to use the latest fashionable thing.”

“Now what I do to offset- like I travel a lot for my work- I carbon farm. I pay people to grow soil. Growing soil is much more climate friendly than growing trees: a hectare of carbon farming soil takes more carbon out of the planet than a hectare of trees. It’s much more efficient. (Michael pays $46 dollars per month to adopt a farmer).”

Phase 2: growing your own food

“About 5 years ago I started to understand that what I had done was really trivial. Most of our environmental impact is caused by the growing and production and waste and transport of food. Until I grew my own food I really wasn’t going to make a difference.”

“I mean the house is in a lot of publications; it has been copied and formed a basis for new government rules, but until we grow food where we live we’re not making any difference.”

“So now I’m trying to grow food. Over there I have two chooks. You can run 2 chooks in about 3 or 4 square meters so I have a little chook house on the side of my house that isn’t used that much. I should be able to grow enough eggs here for two people. The chickens provide eggs that have protein. I like to make omelettes and I can use the eggs for salads. I’m trying to grow the things that I cook, not fancy stuff that I don’t cook.”

Vertical gardening

“And I’m experimenting with two forms of vertical gardens. This one here with my neighbors I’m trying to grow some spinach, some tomatoes, some chilies, some bok choy, parsley and mint, so that I can try to grow, at least some of the greens that I cook with. That’s the important thing.”

“And there’s another form of vertical garden I’m trying to grow here. This is an experiment. I’m trying to grow food on this west facing very hot vertical wall. It would do two things: it would grow food, but it would also shield my roof and cool the house from a hot western sun.”

“Actually plants don’t need soil; they just need water. Soil provides a structural holding medium and the nutrients. It’s the water that liberates the nutrients in the soil. There’s basically no soil in here, but the key thing is water and the nutrients that it liberates to the plants, at least the nitrogen and the phosphorous.”

“So I’m growing grapes over here, the chooks, these vertical gardens, and out front we’re growing rosemary, chilies, limes, lemons, and a whole range of citrus. This is shared by my neighbors and we’re trying to grow food in the street.”

faircompanies: These vertical gardens seem like a new idea, why are you doing it this way?

“It’s more efficient. In this space between me and my neighbor I’ve got about 40 plants; they can share this and have their own coming in there. All this is new. What I’m trying to do is publicize it and make it easy and copyable and affordable. Everything I do is designed to be copied by other people.”