40% House

Sally Harper and Tony Williams have fully renovated their 200 year old cottage using materials and technologies that have been meticulously sourced to be environmentally sensitive and in keeping with a traditional rural building.

The building is one half of an eighteenth century stone brewery with a welsh slate roof. It was later converted into two cottages. The cottage posed a major renovation challenge. It was in a poor condition: the fabric was decayed, there was no insulation, open fires were the sole source of heating, and all water came from a well in the garden.

Why did they want to do it?
Sally and Tony believe strongly that that localised self-sufficiency is the basis of sustainability. Their house is a visionary ‘manifesto’ for a future based on reduced consumption and localised economies.

About the renovation
The renovation combined energy efficiency and conservation of an old building using ecological building practice. Reclaimed and organic materials were used alongside new renewable energy technology. This combined approach addressed Sally and Tony’s concerns about global pollution and natural resource depletion and the desire to create a healthy building from renewable resources. Selecting effective insulation, which was not harmful to the historic fabric or the environment was central to the design challenge of ‘green’ renovation. The walls, roof and solid floors are all insulated with natural breathable materials to allow water vapour to pass out through the building helping to create a healthy mould free environment. Research shows that, without careful ventilation strategies, modern ’tightly sealed’ buildings using impermeable membranes can create both unhealthy and inefficient buildings. “You have to imagine the effects of living in a plastic bag” says Sally.

Heating systems
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 losses 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 a 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.

Pictured: A multifuel burning stove

Structure and Insulation
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 by-product of mining.

 
Pictured: Tony cutting wool insulation

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 and Sally and Tony encountered a conflict between their desire to use traditional natural materials and their desire to use locally-sourced products. In this case they decided to import the hemp from France to establish the principle that this is an important building material which should be reinstated in Britain

Pictured: Extension of green oak frame with hemp and lime fill

Water and waste
They 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. The decision to stay off the mains saved them over £1,000 in connection costs.

What were the main obstacles they encountered?
The cottage is in a designated conservation area and they had numerous battles with the local planning department, which, says Sally, “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. They also faced the challenge of finding performance data that could persuade the building inspectors that the unconventional materials passed the current building regulations.

How did they find out what to do?
Sally had the advantage of a recently completed MSc in environmental architecture from Oxford Brookes University. Despite the strong theoretical backing, she says 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 manufactures. There is no one stop ecological shop or source of experts in Oxford, 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.

Three top tips
1. Identify relative heat losses from the house and energy uses in the house.  This helps you to prioritize elements within an overall ‘green’ design.
2. Be prepared to find independent ecologic 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. Sally and Tony have designed the roof to enable the installation of a photovoltaic array in the roof even though this is currently a relatively less effective ‘green’ investment.  They recommend that other people fit a double coil hot water tank even when they are not yet planning to install a solar panel.

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.