What is the most sustainable structure that you have ever encountered in a city? All sorts of interesting green buildings may come to mind as you contemplate this question but the answer may be right outside your window.
There is nothing that beats nature’s own highly evolved urban habitat: the tree. Stop then for a moment and consider just how remarkable these ubiquitous but inspiring structures really are.
Trees are perfectly adapted to the natural environment in which they flourish, coping with extremes of heat and cold. They are brilliantly engineered to withstand severe mechanical stress while also fending off biological threats. They are built from beautiful, sustainable materials and are powered entirely by solar energy. They produce no harmful waste and turn all their waste products into valuable nutrients. They are perfectly integrated into the wider ecosystem and support a diversity of flora and fauna. In the current search for truly sustainable buildings we could do worse than look to trees for inspiration. As a self-builder with ecological ambitions, this impressive list of qualities became my specification for Tree House, a house that works like a tree.
Tree House was built in 2005 in Clapham, near the centre of London, England. It is unusual to find a single building plot in the heart of this very old metropolis, so when the opportunity arose I decided to make the very best of it. The plot was challenging, not least because it was dominated by a large mature tree. But rather than seeing this tree as a constraint, I decided to create a building that was a sympathetic response to the tree. This meant not only insisting on the very best ecological specification but also responding to the beauty of the tree in the form, materials and details of the house.
This is particularly evident in the front elevation of the house which evokes the tall form and organic liveliness of the tree in its curving timber-clad stair-tower, the movement of the windows framed by salvaged oak beams and the broad sweep of the roof-canopy. Our tree has also found its way into many of the details of the house including the fences that pick up the patterns in its bark, the tree trunks that support our staircase and the dappled light created by stained glass within the building.
In the top room of Tree House great timber trusses burst from a wall of books then branch out to support our roof. Through the glass doors that open on to our little tree-top balcony we can admire the same movement in the structure of the tree, albeit expressed in an infinitely more complex manner. Of the many ideas that have shaped this project, one of the keenest has always been a desire not merely to dissolve the boundary between inside and outside but to unite these spaces with common forms, materials and palette.
There was only one construction material that suited our arboreal dream: timber. We put considerable effort into ensuring that all the timber we used was sustainably sourced, either using new timber which had chain of custody documentation demonstrating a well-managed source, such as that provided by the Forest Stewardship Council (FSC), or using reclaimed timber. Our floors are finished in teak that once grew in the forests of Burma but has since spent over a century in a water works just up the road from our site. Re-use is always the best ecological option when choosing materials.
The toughest challenge was to build a house that was completely powered by the sun. We have achieved this through a combination of a 5kW peak solar-electric (photovoltaic) roof, a ground source heat pump and a high performance building fabric which keeps our demand for energy to a minimum. Put these things together and across the year we produce more electricity than we consume (we export the surplus to the electricity grid).
Although the renewable energy technology is essential to achieving this goal, it is the building performance which matters most. The building is highly-insulated and air-tight with controlled ventilation. This keeps the heat in during the winter and keeps the heat out in the extremes of summer, so we need relatively little heating and no active cooling – all the cooling is passive including external louvers and blinds, ‘passive stack’ ventilation and a pond that cools the air before it enters the house.
In many parts of the world adaptability to climate remains at the heart of building design. I was born in Kuching, Sarawak and I can still remember the house where I lived as a small child before moving to Britain, especially the veranda, which was open to the breeze while also keeping the sun shaded; a good passive design for a hot and humid climate. In Britain we have got used to throwing energy at problems of climate control, rather than designing buildings to moderate the climate passively (no doubt air-conditioning is also much more popular in Kuching today than it was when I was five years old). Yet this rush to fix the problems of interior climatic conditions with energy only exacerbates the problems with the global climate. Better, then, to return to adaptive design that uses passive techniques to provide comfortable interior conditions. We may still need some energy for heating, cooling and lighting in certain conditions, but we should always start by trying to meet these needs through good design rather than energy-hungry technology.
In designing buildings today – buildings which ought to last 100 years – we need to consider not only the demands of the current climate but also how the climate may change over the century. In Britain, people are likely to see more heatwaves and drought in the summer and more intense rainstorms in the winter. Consequently it is vital that our buildings and cities are designed to be naturally both cool and permeable, absorbing the intensity of the summer heat and the winter rain. Which brings us back to trees: providing shade, absorbing heat and always creating delight.
Tree House is genuinely a delight to live in. The warm materials, comfortable interior, abundance of natural light and integration of inside and outside spaces all contribute to a rich and sensual experience which changes across the day. Whatever your ecological priorities may be, make sure that beauty and delight are at the top of the list.
Will Anderson’s books, ‘Diary of an Eco-builder’ and ‘Homes for a Changing Climate – adapting our homes and communities to cope with the climate of the 21st century’ are available from Green Books (www.greenbooks.co.uk).