We are Sally Harper and Tony Williams, and we have extensively renovated our 200 year old cottage using materials and technologies which we have carefully sourced for their environmental sensitivity and their fidelity to traditional rural building. I (Sally) have recently completed an MSc in environmental architecture at Oxford Brookes University.

As we believe strongly that localised self-sufficiency is the basis of sustainability we decided to put our ideas into practice starting with one of the main consumers of energy in our life, our house. We hope that our house can in some degree embody and contribute towards our ideal of a future based on reduced consumption and localised economies.

We installed an integrated heating system which includes a twin-coil hot water cylinder heated by solar thermal panels, a highly efficient wood burning stove amd underfloor heating.

The challenge here was to integrate a variety of renewable or zero carbon energy sources and to create a scheme which could store and efficiently distribute heat. The heat storage was designed to counteract sporadic or short periods of heat generation from renewable sources. A twin coil hot water- cylinder (Oso) which loses less than 10c over a 24hour period, stores heat from 4 square metres of solar thermal panels (AES flat plate solar array) integrated into the roof and heat from the highly efficient (85%) Super Demon (Hellfire Combustion Co) wood burning stove (distributed and installed by Sterland and Elgar Ltd, Heating Engineers, Warwickshire, 01608 663341).

The stove also simultaneously provides the heat for the underfloor heating system. The underfloor heating pipes in turn run through a solid, highly insulated floor, which retains the heat 20 hours.The solar thermal will provide up to 70% of the domestic hot water.

We decided to keep the original water and waste system which were in good working order.

Water comes from the well and is pumped through a water softener to avoid corrosion of pipes. Waste water and sewage pass into a cess pit and then into 140 feet of terracotta pipes buried in the garden. Our decision to stay off the mains saved us over £1,000 in connection costs.

We have insulated the ground floor and the walls using natural materials which both insulate and breathe. For the floor four layers of different materials were employed, whilst sheep wool batts were used for the walls. We have added an extension to the back of our cottage using oak windfall the frame of which was filled with insulating panels of hemp mixed with lime.

The complex structure of the ground floor is designed to achieve a highly insulated solid floor using natural materials which ‘breathe’ and can accommodate the underfloor heating pipes. It is composed of four layers laid on a geotextile filter blinded with sand. The bottom layer is leca (Light Expandable Clay Aggregate -a marine clay with a honeycomb structure the size, shape and weight of a Maltezer) or recycled ‘foamed’ glass blocks, which give an even better insulation performance. This bottom layer is laid dry and loose. Above this is a ‘slab’ or layer of pumice and lime mixed with water a laid wet, which dries to form a solid structure. Underfloor heating pipes can then be fixed on top of the dried slab. Finally the slab is covered with a limecrete ‘screed’. The finished floor surface is a layer of 25mm English limestone flagstones. The pumice provides a ‘permeable’ solid floor essential for the health of the building and effective heat distribution and storage. Pumice is a by-product of mining.

The insulation of the walls has been approached with a similar concern for finding materials that insulate and breathe. The original stone and lime mortar walls are insulated with sheep wool batts. These are placed between wooden batons and faced with Heraklith sheets - a German particle board composed of compressed sawmill waste which does not use formaldehyde glues. The inside is plastered with haired lime plaster.

A new extension at the back of the cottage is constructed of local windfall green (unseasoned) oak. The oak frame is filled with insulating panels of hemp mixed with lime, and rendered with lime plaster. Hemp, which used to be a common crop in Britain, has been effectively banned due to British drugs laws, we thus encountered a conflict between our desire to use traditional natural materials and our desire to use locally-sourced products. In this case we decided to import the hemp from France to establish the principle that this is an important building material which should be reinstated in Britain.

The cottage is in a designated conservation area and we had numerous battles with the local planning department.

The local planning department had no interest in supporting the efforts we were making. They added enormously to our time and workload. There was no flexibility in the planning guidance to permit roof-mounted solar panels and the only way that they finally passed the planners was by mounting them behind a flush rooflight. This solution required complex and expensive detailing and reduced the efficiency of the panel. We also faced the challenge of finding performance data that could persuade the building inspectors that the unconventional materials passed the current building regulations.

Although I had the advantage of a having recently completed an MSc in environmental architecture at Oxford Brookes University, and thus had a strong theoretical background, it still required a great deal of research into vernacular buildings, modern environmental buildings in Europe and contacting specific material experts to create a complementary range of environmentally friendly materials throughout the building.

As with the advice, the materials came from many different sources, some directly from manufacturers. There is it seems no one stop ecological shop or source of experts in Oxford, and thus the web proved the quickest way to find manufacturers or specialist suppliers. Professional associations like the Solar Association are excellent starting points for guidance and contacts. The Natural House Book by Cindy Harris is an excellent practical all round review of energy efficient and ecological choices

What were the improvements in energy performance or the carbon savings?

It is not possible to assess the previous emissions of the house. However, the renovation has achieved two important changes. It has reduced heat loss through the walls and roof by 90%, and has replaced the former open fires with an 85% efficient stove. Given that the stove runs on local windfall and waste wood and the electricity is purchased from a green tariff supplier, the house has very small environmental footprint.

Three top tips:

1. Identify relative heat losses from the house and energy uses in the house. This helps you to prioritise elements within an overall ‘green’ design.
2. Be prepared to find independent ecological manufacturers and buy direct as a way to make ecological materials ‘affordable’ or comparatively priced.
3. Future Proofing – design a ‘green’ energy infrastructure, which can be implemented in steps according to budgets over time. Our roof has been designed to enable the installation of a photovoltaic array there even though this is currently a relatively less effective ‘green’ investment. We would recommend that other people fit a double coil hot water tank even when you are not yet planning to install a solar panel.