Environmental cover-ups

Need a new roof? Well, before you start comparing the cost and durability of slate tiles versus clay, or the pooling potential of felt laid on a flat surface, you might want to consider an option that allows you to help the environment as well as your household. Since domestic dwellings are now being blamed for contributing up to 27 per cent of greenhouse gases, according to the UK’s Department for Environment, Food and Rural Affairs (Defra) and the Energy Saving Trust, it makes sense for all of us to look at how efficient we are, not only in our activities but also in the fabric of the buildings we inhabit.

Around the world, architects have shaken off the scruffy, grass-stained mantel of previous generations of eco-designers and started to produce sleek, stylish homes packed with energy-saving and renewable technologies. Most of the truly high-design, green-to-the-gills structures are new-builds but some ideas can easily translate to existing houses. And, since roof replacement is something most homeowners have to invest in at some point in their lives, it makes sense to start from the top down. Accessible and appealing eco-friendly alternatives include “green” or “brown” roofs, wind turbines, rainwater harvesting, heat exchangers and solar panels.

Roofs made of turf have existed for centuries – in Scandinavian countries they can be seen with pines and shrubs growing out of the top – but now they seem to be sprouting up, literally, all over the place. In Europe and North America they can be found on airport buildings (Amsterdam’s Schiphol), chain restaurants (Pizza Hut), factories (the Ford plant in Dearfield, Michigan), hospitals and a growing number of new municipal buildings.

Green roofs are relatively straightforward to install and maintainence costs – for domestic properties at least – are comparable to standard roofs. As long as the suporting structure is strong enough to take the weight of rain-soaked or snow-covered soil, existing flat and pitched roofs can be greened using just a few layers of specialist materials. And if you have a concrete flat roof, you can convert it into a terrace garden.

The result is a high level of thermal insulation, which keeps the house warm in winter and cool in summer. Green roofs are good sound insulators, too, and go some way towards replacing the natural habitat the house is stifling on the ground. What’s more, if used over a range of buildings, they help cool the immediate environment and offset “heat islands” caused by buildings in urban areas.

While green roofs are usually planted with sedum or prepared turf, “brown” roofs are made from recycled building materials that serve as a growing medium. Construction rubble is crushed up and naturally self-seeding plants – or weeds, as most gardeners call them – take root with the help of a little wind and birds. These roofs lack the lush appeal of their green cousins but still offer most of the benefits.

One level up from the basic green or brown roof can be found outside Barcelona, where Cloud 9 Architects has created the Villa Bio, with a hydroponic roof garden spread over two levels. Mediterranean plants grow on a surface made up of layers of geotextile membrane and volcanic rock. The rock is tradtionally used in the area as a heat insulator and to make lightweight concrete for construction but it’s also beneficial to plants since its porosity helps aerate the ”soil”. Rainwater is retained in the drainage layer of the roof and helps to water the plants.

Capturing the water that falls on your roof and diverting it for your own use later is another way of making your home more eco-friendly. It is not merely about recycling, either, though the reclaimed water can be used for many purposes around the house apart from drinking. It’s also, as London architect Deborah Saunt, who designed a children’s centre with brown roof, a wall of plants and a system to recycle rainwater, points out, about slowing the flow and reducing the amount of water pouring into roads and sewers. Stronger, more frequent storms are one potential side effect of global warming and in many cities serious downpours are already taxing existing infrastructure.

Rainwater harvesting can be as simple as installing pipes that direct it into a storage tank underground. This system can then be enhanced so that water can be used to flush the toilet, irrigate the garden or even supply the washing machine. The UK Environment Agency advocates the practice, arguing that it has “environmental benefits and the potential of significant financial savings”, depending of course on the amount of water your roof or other exterior surfaces are liable to receive.

Of all green roof options, this is probably the least invasive and easiest to install, particularly if you use a storage tank above ground and only use the water for gardening. It’s also easy to see a return on this method if you live in a suitably rain-soaked part of the world.

Heat-exchanging ventilation systems are also devices suitable for installing at the top of a house. Because warmth created at ground level rises, ceilings and roofs are the natural places to site systems designed to ensure that loss of heat is minimised. These systems collect rising warm, moist air and use it to heat cool air which is descending from roof-level intakes, establishing a convection-style current that ensures valuable heat energy is reused many times. Recent developments harness wind power to draw cool air into the sytems rather than using electric motors to drive intake fans.

The next step for eco-minded homeowners is to build a roof that not only saves energy but also generates it through solar panels and wind power.

Solar energy is mostly harnessed at rooftop level either by using sunlight to heat water directly or by collecting energy via photovoltaic panels. The direct method is usually recommended for use in conjunction with a more conventional energy source and is best for providing all of a house’s hot water in summer and some of it in winter. Photo­voltaic (PV) panels consist of cells that collect light energy and convert it into electricity. In many places excess energy produced this way can be sold to the local electricity generator.

California architect Lawrence Scarpa and his wife and colleague Angela Brooks have provided the perfect PV pin-up with their design for their own house, dubbed the “solar umbrella”. It is a light-filled, open array of planes and innovative materials that encourages the free-living, indoor-outdoor quality of life that so many people associate with the US west coast.

Scarpa says he is “inspired by the sheer beauty of solar panels”, which explains why he made a highly visible feature of them, mounting them overhead and vertically to create a canopy and using them as part of the structure of the building. Elsewhere, the roof is fitted with solar thermal panels to heat water for the house and pool and is designed to retain 80 per cent of roof rainwater. Scarpa and Brooks now generate 95 per cent of their own electricity from the weather.

UK Conservative party leader David Cameron has commissioned many of the same features for his home in London’s Kensington. Architect Alex Michaelis of Michaelis Boyd Associaties, whose own home boasts a sedum roof, was brought in to install solar thermal panels and rainwater collectors. But the piece that most intrigued the UK media was Cameron’s wind turbine.

There are now several companies in Europe and the US that market small-scale turbines for homes. Current models are not always viable in built-up areas because the wind rarely reaches speeds high enough without turbulence to make them cost effective. There are also issues of stability (turbines mounted to chimneys to obtain greater height might destabilise the structure, especially in strong gusts), local government building consent and noise .

Still, there is a growing demand for domestic turbines and many people, particularly in rural areas, trust them as reliable sources of power. Architect Bill Dunster, who, along with engineers Arup, designed the award-winning Beddington Zero (fossil) Energy Development (BedZed) in London, laments the fact that wind turbines have had such bad publicity. “We’re testing a couple of models at various sites with good results,” he says, adding that he expects the technology to be available in as little as 18 months’ time.

Ideally any modern roof, particularly on a newly built house, would include some combination of eco-solutions, as most of the architect-designed examples do. A green roof can easily be fitted with pipework for harvesting rainwater, for example, and PV panels can sit alongside thermal versions. And while these technologies are mostly to do with small movements toward sustainability rather than short-term financial rewards, as energy costs increase, and most people agree they must, financial benefits might materialise sooner than expected.

Phyllis Richardson is the author of ‘XS Green: Big Ideas, Small Buildings’ (Thames & Hudson, £14.95).