HPH054 : Building an Autonomous House – with Mike Coe
Mike Coe lives in an autonomous house with his partner Lizzie Stoodley. He shares the story behind this self-build project and why it's ultimately left them with a deeper connection to their environment.
Take a Video Tour of the Autonomous House
Mike has produced a great video about his house that gets into all the details.
Interview with Mike Coe
After many happy years working as an ITV News cameraman Mike Coe had the opportunity to take voluntary redundancy. With an increasing concern about the environment he saw this as a way that he could make a difference, building an ultra-low energy house.
Architects Brenda and Robert Vale Inspired the Project
In the mid 1990s Mike was sent to Southwell, Nottinghamshire, to cover a story about an environmentally-friendly ‘autonomous' house.
Unfortunately the feature never made the ITV News because a bigger story broke, but visiting the house made a lasting impression on Mike.
Brenda and Robert Vale's book (affiliate link)
External Services are Inefficient
One of the reasons Mike brought the provision of water supply and the disposal of waste in-house was because a considerable amount energy is used in providing these services. For example, drinking water is first treated, then pumped to our houses and once it's been used, the waste has to be taken away and the process starts again.
Mike says: “We’ve effectively eliminated the energy that is used in providing those services so that reduces the energy footprint of this house even further, but ironically those factors are not normally considered when looking at the overall energy demand of a dwelling.”
This Level of Autonomy Would Not Make Sense in a City
In a densely-packed town or city centre, becoming more autonomous would not work so well.
Mike gives an example of how space would be needed for the composting chamber as well as a garden to deal with the waste.
Individual waste or rainwater treatment may not be such a good solution on a large scale development either, but it could make more sense on a localised scale (similar to how district heating works).
The House Does Not Have a Heating System
The Cropthorne Autonomous House has an extremely high mass, and all the construction was based around large amounts of concrete and high density concrete blocks.
The mass was surrounded by a very large amount of insulation and then the house was built airtight with a mechanical ventilation system. As the house is specifically oriented to the south it takes advantage of passive solar gains.
Although they did not set out to build a Passivhaus, all the thermal modelling was done using the Passive House Planning Package. So the performance of the house exceeds the Passivhaus standard at between 3 – 5 kWh per m2 per year.
Incidental Heat Gains Help in the Depths of Winter
The house warms up slowly throughout the summer and during the winter months, as temperatures outside drop, the mass begins to give the heat back.
Mike says: “It actually carries through December and into January before you begin to notice that the thermal mass of the building is dropping.”
The building is so efficient that incidental gains – the heat that comes from things like cooking, computers, televisions, etc. – contribute to keeping the house warm.
The Inverted Layout Takes Advantage of Rising Heat
Mike wanted his living areas upstairs and bedrooms downstairs because of the fact that heat rises.
In winter this means that the areas where they spend most time – the kitchen and living room – are the warmest parts of the building. It doesn't matter so much if the bedrooms are cooler because they can throw on an extra duvet.
Also in the summer, if there is a very warm spell, they avoid the problem of not being able to sleep because of overheating bedrooms.
Rainwater is Harvested and Stored Under the House
With no connection to the water mains, rainwater is harvested from the roof and channelled into bulk orange juice transport containers (1500 litres each). These tanks would otherwise be destined for landfill and so are being recycled for this project. Mike bought them direct from the Britvic factory in Norwich.
10 of them store raw untreated rainwater, while the 11th is a slow sand filter which almost completely purifies the water. This leaves the 12th as a storage vessel.
The total capacity of 17 tons is enough for all their water needs for over 100 days.
Taking Responsibility of Resources Puts You in Touch with the Environment
One of the things that Mike really likes about the house is that it puts you back in touch with the seasons and the weather outside.
For example, if there's going to be a prolonged dry spell then they would have to be more careful with their resources and not water the garden or wash the car. So they have to manage their water supply where as most of us just trust that water will be there when we turn on our taps.
Living in an Autonomous House is No Harder
Mike continues: “I wouldn’t say that living in this house is more difficult than living in a house with conventional servicing. I’d say it’s different.”
While they might have to look after their water supply and deal with their waste, there are other things they don't have to worry about. For example, with no boiler that also means no servicing!
Composting Toilets Eliminate the Need for Water to Flush
The composting toilets work much in the same way as any compost heap. In this case human excrement falls into a special chamber together with handfuls of wood shavings, which keep the compost pile healthy. The urine is also separated.
This completely eliminates the need to use water for flushing the toilets. Most countries in the developed world use clean drinking water to flush the toilets which is immensely wasteful.
When human waste and clean drinking water is mixed it also produces a problem substance called sewage which then has to be transported away, separated out and made clean again. This all requires energy.
The resulting compost from this dry system is useful as a fertiliser and can be put straight onto the lawn or plants, etc.
Maintaining a Connection to the Grid has Benefits
The autonomous house is connected to the electricity grid (and there's also a telephone line). The reason for this is that they still draw power from the grid in the evening.
They have a 2.3 kW photovoltaic array which is not that large by most standards but is based on supplying a house which is already very efficient. So the PV system covers virtually all of their energy needs throughout the year. Therefore their net electricity usage is close to zero.
Overcoming Building Control Objections was a Challenge
The only discharge from the house is grey water and that goes straight into a soak away in the garden.
Unfortunately the Building Control inspector wouldn’t accept this approach, despite the approval of the Environment Agency. This meant an uphill battle but it was eventually overcome.
Concentrate Less on Style and More on Resilience
Mike believes that anyone wanting to self build should consider what's going to be important in the future. Will fuel prices continue to rise? He wonders whether we need to concentrate less on style and airy interiors, and build in a little bit of resilience.
Reducing your energy demands down to a tiny amount will certainly mean that rising fuel prices have less impact on you.
Mike has Learnt How Acidic Water is
As with any self build project, Mike has learned a lot along the way. One shocking discovery was that the harvested rainwater started to dissolve their copper plumbing!
This is because rainwater is now extremely acidic due to the amount of carbon dioxide in the atmosphere so it is effectively raining carbonic acid! All water at the autonomous house has to be pH corrected.
Terracotta Tiles Offer a Great Alternative to Carpets!
Mike has terracotta tiles on the floor because if he put down carpets it would insulate the thermal mass and it wouldn't work as effectively.
However, using terracotta tiles has led him to realise a few things. Firstly if they are looked after they will probably last for the lifetime of the building. Even if one cracks it could be cut out and easily replaced.
Secondly Mike has realised that a lot of the economy thrives on waste. In the case of carpets he suggests that they will probably be replaced every 15 – 20 years. In the UK alone that amounts to half a million tons of carpet going to landfill every year.
Mike says: “If you eliminate the waste, so if everybody tiled their floor with terracotta floor tiles and nobody bought any more carpets it would be a big problem for a lot of people who would lose their livelihoods. So I think there is an irreconcilable payoff between having a healthy, thriving, functioning economy and economising where it really matters in terms of environmental damage and consumption and so forth.”
Find Out More
Visit Mike's website on the Cropthorne Autonomous House.
Transcript
Download a transcript of the interview with Mike Coe.
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As an experienced cameraman today's guest, Mike Coe, will also be involved in our documentary should it get the go-head.
