Tag: Cropthorne

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.

Follow Mike Coe on Twitter.

Transcript

Download a transcript of the interview with Mike Coe.

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May 21, 2014
What is an Autonomous House?

Do you feel that you’re lacking a connection with your environment?

Would you like to live in a house where you are in control of the services?

This article is a case study of a couple who created an autonomous house. We find out why they did it and how different it is to live this way.

Autonomous Means Possessing a Large Degree of Self-Governance

Mike Coe and Lizzie Stoodley built themselves an autonomous house in Cropthorne, Worcestershire. Although being autonomous might imply no connection to the outside world, in their case this is not strictly true because they are linked to the grid (albeit to export more electricity than they use!).

If they were completely self-sufficient and off-grid in all respects they would have an autarkic house, but autonomous is a better description of their home. They have no gas supply, they derive their water from harvested rain and they deal with their own human waste.

Architects Brenda and Robert Vale Inspired Them

The initial seed of an idea came in the 1990s, before they had any plans to build a house. Mike was an ITV News cameraman and he was sent to Southwell, Nottinghamshire, on an assignment to do a story on a new kind of house.

Mike describes his visit: “Nobody had the faintest idea what it was. Only when I got there did I realise that it was fascinating. We did an interview with Robert Vale and he showed us around and I thought this is a really interesting project.”

The feature was never shown on ITV because another story broke, but Mike’s journey was not in vain. He had been inspired.

Many years later Mike and Lizzie were considering a long-term plan to leave London and live somewhere less hectic, when they returned to the idea of an autonomous house.

Increasingly concerned about what the human race was doing to the environment and with a strong desire to take action somehow, the ideas came together in their ultra low energy house. It would be based on the house at Southwell but would try to take everything to the next level, with improved materials and greater experience, etc. As this was a once-in-a-lifetime opportunity they wanted to do this properly and take the ideas as far as was sensible.

In 2006 Mike and Lizzie bought their plot of land

Passivhaus Offered the Best Approach

Mike was convinced that the basic configuration of Brenda and Robert Vale’s house was correct. It had a very high thermal mass – based on a concrete core – surrounded by a huge amount of insulation, built as airtight as possible with super high performance windows. Although Brenda and Robert Vale’s house had a small wood stove, Mike and Lizzie believed they could create a house that didn’t need a heating system and just relied on incidental heat (body warmth, cooking, heat from appliances and so on).

While the house was designed and constructed using Passivhaus principles it hasn’t been certified, although this could (easily) be done at a later date. In fact the primary energy requirement of their house is between 3 – 4 kWh per m²per year, which is four to five times better than the Passivhaus requirement.

An Inverted Layout Takes Advantage of the Fact That Heat Rises

In terms of design the house is upside-down. So the living area is upstairs, taking advantage of the fact that heat rises. In a house with no heating it makes sense to live where it’s warmer during the winter. Also, during very hot summer weather, the bedrooms, being downstairs, stay cool and are therefore more comfortable.

If Mike ever builds another house he would definitely do it the same way again.

You Must be Adaptable to Live Like This

Living in an autonomous house requires more thought than a conventional dwelling. However, it’s good thought! The user needs to understand how the building works in order to get the most out of it. For example, controlling the temperature is about considering what to do with the heat. During the summer, Mike and Lizzie warm up the core of the house to a comfortable temperature. They make sure that they close windows and doors when they need to store up heat for the winter. Also, in autumn and winter the mechanical ventilation system is in heat reclaim mode whereas during the summer they don’t reclaim any heat.

Mike says: “You’re much more in touch with the seasons and the outdoor environment and you modify your behaviour accordingly. You have to be prepared in the depths of winter to wear a jumper.”

Responsibility for Resources is Back with You

In today’s world, so long as we have money we know (or perceive) we can have the resources. This not only shifts the responsibility onto somebody else – our service providers – but it distances us from what we’re actually doing to the environment. To live in an autonomous house it is necessary to be more in touch with the environment which Mike sees as a very good thing.

Mike and Lizzie have 17 tonnes of water storage in their basement, but they still need to modify their behaviour if they are anticipating a prolonged period of dry weather. This might mean not cleaning the car or taking showers less often.

“We derive all of our water supply from water that falls on the roof. We store it, we purify it, we drink it, we wash in it and we wash our clothes in it. And it ends up back in a soakaway in the garden.”

The same amount of water enters the site as would have done had the house never been built. All they do is borrow it.

Mains Electricity Makes Sense at the Moment

Mike explains that it’s not environmentally and economically sensible to go off-grid if you have access to a mains electricity supply. This is because storing electricity is not straightforward. For example they could use banks of lithium or nickel metal hydride accumulators but they contain a lot of chemicals. Plus, with this set-up there might still be trouble supplying the house at periods of peak demand.

So, at the current time there is little financial or environmental advantage. Instead they effectively use the grid as a battery!

Most of the electricity generated by their 2.3kW ground-mounted photovoltaic array gets exported because the energy demands of the house are so low. At night time they consume power from the grid, but it’s a small amount. The total electricity bill for the house is in the region of £350 per year and as the payment they receive from the photovoltaic array is about £900, they make about £500 income.

Mains Water and Sewage Systems are Not Efficient

There’s a lot of energy involved in providing houses with clean water and removing the sewage.

While doing his research Mike discovered that 30 – 40% of the water consumed in a normal house is used for flushing the toilets. In most cases it is also clean drinking water, which is of course very wasteful.

Human waste is actually quite a useful substance because it has similar properties to a fertiliser. Mike sums it up well: “What we normally do is we mix useful human waste with useful clean drinking water and we produce a problem substance called sewage, which we then have to pump several miles using energy and process it in a local sewage treatment plant.”

The composting toilet being installed

Composting Toilets Made Sense

With heating and lighting, adjusting lifestyle can often result in huge energy savings. However, when it’s comes to human waste you can’t really reduce the number of times you need to go to the loo! That’s why Mike and Lizzie were keen to bring all those services in house and provide them without using any external energy.

Mike explains how it works: “Every two months, with two of us living here, we have to maintain the chamber which means we have to drain out all the liquid compost and we have to take out the solid compost [that’s mixed with wood shavings], but by the time you come to do that it genuinely isn’t unpleasant.”

This compost then goes on the garden and this also means that they don’t need to buy any fertilisers.

In the Event of Fuel Shortages, They Would be Well Placed

Building an ultra low energy house is in a sense adding an element of autonomy, because you’re reducing your reliance on external fuel supplies. Reflecting on how their life would alter in times of scarcity or blackouts, Mike says they would stay warm because there’s no heating system to go off! There would be no issues with their water either. Electricity would be fine during the day but they might be inconvenienced with a prolonged power cut.

Running an Autonomous House is Rewarding

Mike and Lizzie have never looked back since embracing this way of living. Mike concludes: “The main thing is you have to think and you have to want to be responsible for your actions. That isn’t a hardship – it’s quite rewarding. I think it’s a good way to live.”

October 18, 2013