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The challenge of creating sustainable housing

Dr Susan Roaf lectures at Oxford Brookes University, School of Architecture and lives in the Oxford Ecohouse which she designed

Does sustainability have implications for architectural form? asked New Zealander Peter Diprose in his doctoral thesis at Auckland University. He concluded that sustainability may have the potential to create novel forms, but no one 'sustainable' aesthetic is likely to emerge.

Instead, a raft of responses will emerge with elements reflecting the broad range of issues the subject entails.

These issues relate directly to fundamental environmental challenges facing us in the twenty-first century.

They include:

Carbon dioxide emissions, the greenhouse effect and climate change Ozone depletion Pollution

Extinction of species and destruction of habitat Population increase and development Resource depletion.

I believe we are capable of meeting these challenges and have the tools and knowledge to create sustainable buildings.

Solutions lie, not with HVAC engineers or planners, but with architects. Because the answer to the question 'is the building sustainable?' is always 'it all depends', and that is 'on the architecture' - how the designer 2than electricity, because generating our electricity is only between 25 per cent and 36 per cent efficient.

Gas resources are depleting, but by the time our reserves have dwindled the solar revolution should enable us to heat our homes and water by electricity generated from the sun. We cannot rely on oil, which is commonly thought to have a total of around 50 easily-accessible reserves left globally.

As designer and builder of the Oxford Ecohouse I have learned firsthand the benefits of very low energy bills. Since April 1995 gas bills for our six-bedroom house have been about £13.50 a quarter, and electricity bills £10 a month (both exclude standing charges).

The house was built without the aid of computer simulation, using lessons learned from master builders (modern and ancient) of the European solar-design community and the Middle East, where I lived for many years. Our house has proved to have one of the lowest energy consumptions in the UK, hence one of the lowest environmental impacts. It provides lessons that can be transferred to future house designs.

The government has predicted the need for 1.1 million new houses in the South-east of England between 1996 and 2021. It will not matter if these are built in high-density city sites, in 'compact cities', or on greenfield sites if they are environmentally profligate. What matters is that each has a minimum environmental impact.

Key points for sustainable housing

Tony Mould, energy and environmental consultant at Tweed Nuttal Warbuton, has some key points to be considered in creating sustainable housing.

Site: save natural habitats where possible. Turn the building away from biting cold winds. Shelter it with trees and planting.

Orientation: align buildings with main living and bedrooms within 150 each side of south to save on heating. Avoid houses shading each other from sun.

Building form: minimise the surface area of building to minimise heat loss.

Shade the building interior from the high summer sun, especially from the west where the hottest air temperatures are combined with the low western sun.

Building envelope: be mindful of exposure. Maintenance becomes an issue in Life Cycle Costing analyses so choose materials that do not need frequent maintenance and repair. Brick has an advantage, requiring only minimum maintenance. At every main entry point, provide a draught lobby, porch, or sunspace to form an air lock to control air movement into and out of the building.

Insulation: choose insulation materials for their environmental benefits as well as their performance.

The thicker the insulation under the floor, in walls and the roof, the warmer the building will be in winter and the cooler in summer. Design to minimise cold bridging.

Detail design to reduce energy leaks: decide the thermal resistance appropriate to each building element.

The lower the U-value of an element the better its resistance to heat transfer, keeping the interior warm in winter and cool in summer. All elements cannot have equal thermal resistance, but each should be the best of its kind. Masonry construction is not always airtight and detail design should minimise air leakage.

Supervision of site work should ensure that details are built as designed and that shortcomings in construction do not prejudice performance.

Ventilation: this is used to remove stale air and odours and to heat and cool buildings. Never use mechanical ventilation where opening windows or passive stack solutions can work, because it uses extra energy. Natural ventilation should be controlled - not just haphazard air leakage.

Daylight: windows to the south will catch the light, that can be used deeper in the building via internal windows to light internal spaces, reducing the need for artificial lighting.

Building mass: lightweight construction, such as a timber frame, warms up and cools down quickly. Buildings of heavy construction, for example masonry, have more thermal mass. The masonry acts like the bricks in an electric storage heater, absorbing heat when it is abundant and radiating it again as the adjacent air temperature drops. A passive solar building should have well-placed thermal mass to act in this beneficial way, assisting fuel economy in winter and comfort conditions in summer, and reducing the magnitude of daily temperature fluctuations.

Embodied energy and materials: embodied energy is that used in the manufacture and transport of material to site. Specifying the most natural products available with a minimum of processing, and sourcing them as close to the site as possible to minimise transport impacts would seem to be desirable, but consideration should also be given to how long they will last and what they will require in terms of maintenance and renewal. Recent studies consider not only embodied energy of materials, but also the energy used in their maintenance and replacement over a 60 year service life - which is what lifecycle costing is based on. Durability and product life are key factors in ensuring the sustainability of building. Brick performs well in this context, we know it can last centuries and still look beautiful.

Heating systems and controls: choose the lowest energy, or CO 2emission, heating system available. The greatest influence on the comfort of the occupants of the building is the weather and the use and control of the heating system. The required heat output is reduced by the thermal insulation of the building fabric and by the heat generated by solar gain and the occupants and their equipment. With a well-insulated building and thermal mass placed correctly it is possible to keep heating energy consumption to a minimum.

Condensation: dampness in buildings is frequently caused by condensation of moisture from air of high humidity on cold surfaces. Follow three simple rules to avoid condensation:

Eliminate cold bridges from construction as they introduce cold surfaces internally on which moisture condenses Provide ventilated air locks such as front porches and rear sunspaces where wet clothes and damp washing can be hung to dry.

Use passive stack ventilation for the kitchens and bathrooms which are areas where high humidity is created.

Use water-based paints on all surfaces to enable moisture to be absorbed into the building structure, so preventing its build up in the internal air of the house.

Water conservation: provide water butts to collect rainwater and consider greywater systems.

Solar water heating: in most years a solar water heating system can provide, free, between 50 and 75 per cent of the annual hot water requirement of a house.

Photovoltaics or solar electric systems (PV): new houses can easily accommodate 500W of PV panels on southfacing roofs. This should cost between £2000 and £2500 for multiple systems, which can generate much of the basic electricity requirement of the house for 20-30 years.

Methods of measurement

Sustainable design requires that design and construction waste should be minimised, local communities be included in developments and building performance targets set and met. These targets can include SAP ratings for energy consumption. A SAP rating of 90 plus is not too ambitious a target to achieve with sensible design. Another target is the 'Ecological Footprint' of a building. This is a more holistic tool and measures a household against the amount of land required to support its lifestyle.

It assesses transport, energy, water, waste, house and garden and purchasing.

Another new tool is 'Envest', a very detailed and user-friendly programme designed for evaluating the environmental impacts of new housing; like BREEAM for Housing it is produced by the BRE.

This is where the architecture becomes of vital importance. Everything noted above and more has to be considered for twenty-first century buildings. Aesthetically houses can look however the client and the architect decide, but they will have to perform sustainably. We are in the new age of performance-driven architecture and, increasingly, this is what clients will be demanding. What will the new architecture look like? It doesn't matter. How will it perform? Very well indeed.

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