Sunny side up

One month into his self-build project and the plot is ready for the builders. However, the climate can affect the design - even in Clapham

Today the first sod was turned. It is precisely two years since I first set foot on the tiny patch of urban wilderness that is now our building plot, and just under a month since I explained on these pages my plans to build an eco-house in the middle of the urban jungle. Well, a small plot amid the terraces of Clapham, south London.

Today the first sod was turned. It is precisely two years since I first set foot on the tiny patch of urban wilderness that is now our building plot, and just under a month since I explained on these pages my plans to build an eco-house in the middle of the urban jungle. Well, a small plot amid the terraces of Clapham, south London.

The latest hitch arose when our contractor's insurers quoted a premium four times higher than his estimate. Lloyds' underwriters may be nervous about groundworks in London's shifting sands but our expensive piled foundations ought to make the house more robust than trenches of concrete. If the insurers can't be persuaded, my budget will also be sinking deep into the brown.

But this is not a day for financial nail-biting. Up to now, the pleasures of self-build have been entirely cerebral. I am finally enjoying the more elemental experience of purging and renewal as our overgrown, rubble-strewn plot is stripped back to the naked earth, ready for the building to begin. All that remains is the tree that dominates the plot and a great empty volume of air where our house will grow.

When I first confronted this big three-dimensional nothingness, the complexity of a house - any house - suddenly seemed overwhelming. Thousands of choices had to be made to mould the emptiness into spaces, structure and details, yet each choice seemed to beg a thousand questions.

I quickly discovered that design is not a beautifully rational process but a muddling through in which competing interests rise and fall with the phases of the moon. In this mix, the constraints of the site were invaluable in forcing practical form upon the ideas and dreams that we brought to the project. We took our responsibilities to protect the tree, to meet the conditions of the planners and to respect the interests of our neighbours very seriously. Another site characteristic, often ignored by contemporary architects, was particularly important to us: the climate.

Climate sensitivity was once the starting point for all building. Across the world, vernacular houses are designed to exploit the warmth and light of the sun, the cool earth and the shelter of the land. In the era of cheap fossil fuels, all this was forgotten as architects could create comfortable interiors regardless of the external environment. Victorian builders, like developers today, replicated their pattern-book villas willy-nilly, knowing that a plentiful supply of cheap fuel would keep their buyers happy. If we are to reduce our dependence on fossil fuels, we need to rediscover climate sensitive building. The Beddington Zero fossil Energy Development (BedZED) in Sutton, south London, is an impressive attempt to do this.

The terraced houses are a contemporary take on "passive solar" design, using huge south-facing windows and thick concrete walls to trap and store the sun's energy. Architect Bill Dunster describes this as the "warm cave" approach, acknowledging the climatic wisdom of our earliest homemaking forebears.

As our plot has no southern aspect, we cannot build a warm cave, although big windows to the east and west will bring energy-saving daylight deep into the house. We can however pitch our roof to the south and harvest solar energy with technology: solar panels and photovoltaic (PV) modules. Government grants will help with both.

Solar panels are radiators in reverse: the sun heats the panel which then heats the water piped across it. PV modules are at the other extreme of technology, using sophisticated semiconductors to turn light into electricity. As their efficiencies improve and costs fall, PVs offer real hope for large-scale but unobtrusive renewable power generation.

If you are building a house or an extension, include a roof with a southern pitch. If you have a south-facing roof already, consider its potential. You don't need blazing sunshine for solar hot water: even in gloomy years you can get at least half of your hot water from your roof. With PVs, you can generate a decent slice of your power needs as well, selling to the Grid when you don't need it and buying it back when you do. We aim to go all the way: by specifying an ultra-efficient house, we will meet all our needs from our little roof-top power station.

Closing the gate on my newly turned plot, my thoughts turn to the history of the site. The plot was once part of the garden of a grand villa in Thomas Cubitt's 19th-century Clapham Park development. It doesn't take me long, following the block round, to reach one of the remaining houses from his ambitious scheme. It looks well-built - brownie points for sustainable resource use - but its structure is defined by the chimneys that rise within to the crowded ceramic pots on the roof. This house was built for people who could afford not only plentiful coal but also plentiful servants to shovel it. There will be no chimneys on Tree House, no fireplaces and certainly no servants. Now is the time for planners and developers to rethink their own servitude to architectural styles that are no longer fit for the environmental demands of the new century.

FINDING AN ARCHITECT

I found an architect relatively easily because I wanted something very specific: a London-based ecological architect with experience of working with self-builders. The firm I chose, Constructive Individuals ( www.constructiveindividuals.com), has been the perfect creative partner. The more you can define your own interests, the more likely you are to find an architect who will draw your dreams as well as their own.

The Royal Institute of British Architects has a database of members and practices (call 020 7307 3700 or view online at www.architecture.com). If you want an architect with green interests, try the Association of Environment Conscious Building ( www.aecb.net). Always ask for references, see previous work and talk for as long as is decent with previous clients.

For solar hot water grants, visit www.clear-skies.org or call 08702 430 930. For PV grants, contact the Energy Saving Trust on 0800 2983978 or visit www.est.org.uk/solar