Buildings use about half the energy industrialised countries consume. Much of it could be saved, conserving resources and reducing our contribution to global warming. Energy efficient housing has already been tried and tested in several countries, with some success.
Between 1975 and 1977, building researchers and designers in North America and Scandinavia pioneered a radically new approach to reducing heat loss from buildings, now called 鈥榮uperinsulation鈥�. Conventional buildings lose most of their heat by simple air leakage. Superinsulated buildings are firmly sealed against draughts, with a controllable ventilation system to provide fresh air in winter. In Sweden, all new houses must by law have fewer than three air changes per hour, tested at a pressure difference between inside and outside of 50 pascals. In superinsulated houses this figure is often brought below 1 air change per hour, while in a typical British house there are 10 air changes per hour under the same conditions (see Table 1).
By the late 1980s, there were more than 100 000 superinsulated dwellings in North America and Scandinavia, where most houses are built of timber. But the problems of adapting these techniques to houses built of brick and concrete prevented superinsulation being applied on any large scale in Europe until the early 1980s. Most of Britain鈥檚 houses-new and old-are put together with little regard to energy efficiency . In the rest of Europe, however, the technique is beginning to take root.
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The Netherlands now has more than 1000 superinsulated houses. In the town of Castricum, 40 kilometres north of Amsterdam, a house built in 1989 has walls containing 120 millimetres of CFC-free polyurethane foam in the cavity between the inner and outer brick layers, about three times as much insulation as normal. Both the roof and the ground floor of the house have similar levels of insulation. Its windows have wooden frames because wood is a better insulator than plastic or metal. They look like ordinary double-glazed windows, but they insulate as well as quadruple glazing, because the 15 millimetre space between the panes is filled with argon, an inert gas which transmits less heat than air. The outer face of the inner pane of glass also has a low-emissivity coating, containing silver oxide, which reduces heat losses by radiation by 80 per cent.
On the warm side of the roof insulation is an airtight polyethylene barrier against water vapour. In timber buildings the barrier stops water vapour entering the structure of the house, where it would condense and rot the wood.
Ventilation is provided by a system of air ducts and two small fans. One fan blows air into the house and supplies it to the living/dining rooms, hall and bedrooms. A second fan exhausts air from the bathroom and kitchen, where most moisture and odours are produced. Stale, warm air is passed through a heat exchanger which transfers 85 per cent of its heat to the incoming cold, fresh air.
More heat for your money
To heat the rooms of the Castricum house requires only a fifth of the energy used by an ordinary new Dutch house-less than 10 gigajoules per year instead of 50 gigajoules. It costs no more than normal Dutch 鈥榮ocial鈥� housing (government-supported private housing), as money normally spent on installing central heating is used to reduce heat losses. A tiny heating system of two small gas heaters on the ground floor is all that is needed. Even when outside temperatures fall to -10 degrees, this house feels much more comfortable than a conventional one because there are fewer downdraughts from the walls and windows. In a small city in the Netherlands, Schiedam, many new houses have almost this level of energy efficiency .
The Castricum house was also designed to use electricity more efficiently, and draw as much of it as possible from a renewable energy source. By choosing energy-efficient lights and electrical appliances, and redesigning the ventilation system to use more efficient motors and wider ducts, the total electricity consumption was reduced by 70 per cent to 3.4 gigajoules (960 kilowatt-hours) per year. The house has about 30 square metres of solar cells on its south roof, which generate electricity at a rate of up to 2.5 kilowatts in bright sunshine. Averaged over the year, the sun supplies 80 per cent of the house鈥檚 electricity. In winter, this is supplemented by a tiny (500 watt) gas-fired generator, whose waste heat warms the house. Solar electricity is not as cheap as electricity from fossil fuels in cloudy northern Europe, but the cost of solar cells is dropping sharply.
In Germany there are several thousand buildings designed to minimise damage to the environment. One of the most interesting was designed and built in 1989 in Tubingen by Johannes Werner, of the energy consulting firm EBOK. He wanted to construct a low-cost house that would reduce energy consumption by 85 per cent compared with that of an ordinary house.
The position of the Tubingen house is not ideal: its main axis runs from north to south, so its windows gain less heat from the sun in winter than on an ideal, south-facing site. But its walls, built of large calcium silicate blocks 175 millimetres thick, are externally insulated with 185 millimetres of expanded polystyrene and then rendered. Such a wall insulates three times better than that of a typical German house built of porous clay blocks 300 or 360 millimetres thick and the materials take less energy to make and cost less.
Werner originally planned to insulate the walls on the outside with mineral fibre. But he found nothing that would fix 180-millimetre thick slabs of mineral fibre, so had to use polystyrene instead, which takes slightly more energy to manufacture. There is also 100 millimetres of expanded polystyrene over the ground floor. The walls are insulated externally down to the foundations 0.9 metres below ground, and Werner used highly insulating concrete blocks where the floor and wall insulation meet. This combination reduces heat losses through the foundations to a fraction of normal.
The roof has 330 millimetres of mineral fibre between the rafters. Great care was taken to reduce the cross-sectional area of the wood-even wood transmits heat three times faster than mineral fibre-and to seal the seams of the vapour barrier, which is made of high-quality polyethylene 0.2 millimetres thick. All the windows are double glazed, argon-filled and selectively coated to reduce heat loss even more.
The upper storey of the house was designed to be let, so it has a separate external staircase. The concrete floor sep-arating the two storeys is not insulated as both are assumed to be warm. However, the staircase and the balcony are self-supporting steel structures. The only heat loss from the rest of the house is then through the thin pieces of timber which pass through the external insulation and tie the staircase and balcony to the calcium silicate blockwork.
On grounds of how much it would cost to buy and install, and electricity consumption, Werner chose a Swedish exhaust-only ventilation system. A small fan constantly extracts air from the kitchen and bathroom, and incoming fresh air passes into the bedrooms and the living/dining room through inlets close to radiators that warm it. The top half of the building had a leakage of only 0.9 air changes per hour when tested at a pressure of 50 pascals, most of it through the wooden roof.
In the nearby town of Sindelfingen a 鈥榮tate-of-the-art鈥� house was built in 1989-90 for a public exhibition. The internal walls and floors are made of concrete, with external walls of timber, insulated with 400 to 600 millimetres of cellulose fibre obtained from waste paper. The foundations are insulated with foam glass, rather than with the more usual plastic foams. The house even has a turf roof, which takes less energy to produce than concrete or clay tiles.
Winter without fuel
The Swiss lowlands can suffer months of near-freezing fog in winter. Even so, 10 semidetached houses being built in Wadenswil, a small town overlooking Lake Zurich, will use little or no fuel for heating. The concrete walls of the houses are externally insulated from the eaves to the bottom of the cellar wall with 180 millimetres of (CFC-free) extruded polystyrene. The cellar floor has 120 millimetres of insulation below it. The timber roof has three successive layers of insulation-40 millimetres of mineral fibre, 60 millimetres of extruded polystyrene and finally 180 millimetres of mineral fibre between the rafters. It also has a polyethylene barrier to water vapour, which is tightly sealed between the two inner layers of insulation.
Windows facing north, east and west let in about 40 per cent of the sun鈥檚 heat and light energy, but they also have exceptionally low heat losses-about 11 per cent as much as single glazing. They use quadruple glazing: two outer panes of glass and two inner films of polyester with low-emissivity coatings containing copper oxide. The three inter-pane spaces are all filled with argon. These remarkable windows let in nearly as much light as a traditional double-glazed window, yet they insulate better than most British walls. Their U-value-a measure of thermal conductance-is about 0.65 watts per square metre degree (W/m2K); the lower the U-value, the better the insulation. The south-facing windows, designed for high solar gains and low heat losses, are triple-glazed. The two inner glass panes have selective coatings, and both spaces between the panes are filled with argon. Their U-value is about 0.85 W/m2K. The houses will be very well sealed when closed up in winter, and windows will open for maximum cooling in summer. The mechanical ventilation system incorporates a heat exchanger, and incoming air is further warmed as it enters the house through a buried tube.
The electrical equipment in the houses will be among the most energy-efficient in Europe. There will be a system to pre-heat the cold mains water, by recovering about 50 per cent of the heat in the waste hot water from showers, sinks, dishwashers, etc. The total energy consumption of the houses should be 20 per cent of normal. Four of the houses have about 30 square metres of solar heating panels, integrated into the south walls and glazed with polycarbonate 鈥榯ransparent insulation鈥� (see 鈥楶lug into the Sun鈥�, New 杏吧原创, 22 September 1990). They heat water which is stored in an insulated tank, and will also be used for heating rooms. The other six houses have a few square metres of solar panels, mainly for heating water in summer. The backup heating system for all houses is bottled propane gas, and one or two bottles should be enough to keep one house warm through a hard, frosty winter. No gas should be needed in mild winters.
These measures added about 15 per cent to the cost of building these houses. Cheaper materials have halved the cost since 1980, and German experts such as Wolfgang Feist of the Institut Wohnen und Umwelt (housing and environment institute) in Darmstadt think that it could drop as low as 5 per cent. However, these measures are likely to reduce household energy bills by less than 拢500 per year, and the extra initial cost is between 10 and 30 times as much as this.
In the Netherlands a national environment plan will raise the price of gas and electricity, and use the money raised to fund investments in more energy-efficient buildings. In future, tenants and owners of all non-domestic buildings intending to use more than 1.5 kilowatts of electricity will probably first have to formulate and implement an energy efficiency plan and obtain an 鈥榚nvironmental permit鈥�. New buildings will have to incorporate energy efficiency improvements of long term benefit, irrespective of cost.
In Germany too, people accept the need for increased energy taxes, to be used for loans or grants to property owners making improvements in energy efficiency. As in Britain, millions of old German buildings have solid masonry walls which lose heat 10 times as fast as the most energy-efficient modern buildings. The Institut Wohnen und Umwelt has suggested to the German government that grants for wall insulation should be conditional on it being a reasonable thickness-for example 150 millimetres of mineral fibre-as part of the effort to cut carbon dioxide production by 80 to 90 per cent over the next 60 years. Buildings with less insulation cannot save enough energy.
Scandinavia and North America pioneered superinsulation in wooden buildings, and continental Europe is catching up fast, within a building tradition very similar to Britain鈥檚. But in Britain, it seems we still have far to go.
David Olivier is principal of Energy Advisory Associates, an energy efficiency consultancy. For further details of theses and other projects telephone 0908 220182. James Bedding is a freelance writer.
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1: How to beat British energy inefficiency
Most British homes use energy inefficiently. Only 19 per cent of homes in England and Wales that could benefit from cavity wall insulation have it. Less than one-third have double glazing. The latest (1990) building regulations increased the required roof insulation for new houses from 100 to 150 millimetres, but only 43 per cent of existing homes meet even the old regulations, according to the Department of Energy.
The National Energy Foundation is an educational charitable trust set up in February 1990 to advise on ways of saving energy. It has devised a computer program that compares the energy efficiency of different homes on a 10-point scale-the National Home Energy Rating (NHER). Homes built to the latest regulations score between 6.5 and 7, while British homes score an average of 4.3, with more than 3 million of them scoring less than 3.
Last September the Leicester Ecology Trust opened its 鈥楨cohouse鈥� to show people how to make their houses more energy efficient. The trust chose a detached council-owned house, built of bricks in 1939 with little attention to energy efficiency, to demonstrate a range of energy saving measures. Some, such as draught proofing, low-energy light bulbs and thermal curtains, quickly save money; others, such as floor insulation, are likely to make economic sense only as part of necessary repairs. Jonathan Cattell, the project鈥檚 development officer, has worked out the possible savings resulting from improvements to a home with a heating bill of between 拢300 and 拢400 per year.
Simple draught proofing around doors and windows costs about 拢60 for a three-bedroomed house with 10 windows. It saves from 拢20 to 拢60 a year. This is the easiest way to reduce the number of air changes per hour, which may be very high in an old, draughty house.
Installing a 150-millimetre layer of mineral fibre across the loft floor costs around 拢160 and saves around 拢50 a year, while cavity-wall insulation costs around 拢350 and saves a quarter of the bills. All these improvements pay for themselves after one to six years.
Walls that have no cavity must be insulated externally or internally, most easily with mineral fibre supported on panels of stainless steel mesh. These measures probably make economic sense only as part of repairs. External insulation costs around 拢15 per square metre; internal insulation is cheaper at 拢7.50 a square metre, including internal redecoration or rendering. External insulation does not reduce room space, and it allows the fabric of the building to help maintain an even internal temperature. Savings are equivalent to those for cavity wall insulation, and can pay back in five to 12 years.
In a poorly insulated house about 10 per cent of heat is lost through the floors. Insulating a concrete floor with a layer of CFC-free expanded polystyrene costs between 拢4 and 拢5 a square metre. Suspended floors can be insulated by laying mineral fibre on chicken wire stapled between the joists; this costs 拢4.50 a square metre. These costs do not include the expense of relaying the floor, but the measures can bring savings of 6 per cent on fuel bills, and pay back in seven to 14 years.
Many houses still have only single glazing. But double glazing often makes sense only when windows have to be replaced. Installing it adds 10 or 20 per cent to a typical cost of 拢2000 to 拢4000 for 10 windows, so the payback time is eight to 16 years. Putting in a secondary sliding window system costs about 拢850, and would not save enough to pay off the interest at current rates.
Cellophane film works almost as well as double glazing for windows that are never opened: it is the trapped air rather than the second barrier itself that acts as an insulator. Slightly thicker and stronger than film used in the kitchen, it can be highly cost-effective at about 拢2 a window.
A traditional conservatory can help heat the house, especially if it is used only on sunny days, and sealed off on cold, cloudy days. Air heated by the Sun can migrate through internal windows and circulate around the house. In summer, a conservatory can also help cool the house: heated air passing through vents in the conservatory roof draws cooler air into the house, through windows on the north-facing side. A south-facing conservatory is particularly effective in spring and autumn; Cattell says that it can save up to 30 per cent of annual heating bills.
According to Cattell, the most neglected feature of many houses may be gas boilers that discard heat through their flues. Many conventional boilers have a peak efficiency of about 75 per cent on installation, but run at less than 50 per cent efficiency after several years. Gas condensing boilers can have peak efficiency of over 95 per cent, yet they account for less than 5 per cent of the 15 million gas boilers used in Britain for central heating, according to the Department of Energy.
Some people blame the poor insulation in many houses and industrial plants on the withdrawal of government subsidies. According to the Association for the Conservation of Energy, which represents companies manufacturing low-energy products and equipment, funding to the government鈥檚 Energy Efficiency Office has been halved in real terms in the past five years.
The government has withdrawn grants for loft insulation except for people on income support. At the same time people are spending half as much on cavity wall insulation as they were in 1987. Sales of boilers and radiators have dropped by a quarter since 1988, while sales of double glazing and heating controls have dropped 34 per cent and 20 per cent respectively over the same period.
Every kilowatt hour of electricity generated from fossil fuel results in the release of 1 kilogram of carbon dioxide. According to the National Energy Foundation, if every house raised its rating on the NHER scale by one point, householders would save a total of 拢1.8 billion a year, and Britain鈥檚 emissions of greenhouse gases would drop by 4 per cent, reducing our contribution to global warming.
James Bedding
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2: Superinsulation the Dutch way
The city of Schiedam in the Netherlands, population 70 000, completed 180 鈥榤inimum energy鈥� dwellings in 1983. They represent the first large-scale application of superinsulation in continental Europe, and use only 10 to 15 per cent of the energy needed to heat previous Dutch dwellings.
The houses are insulated with about 200 millimetres of expanded polystyrene outside the concrete walls, below the concrete floor and in the roof. Even the concrete foundations are insulated. The windows are double-glazed and fitted with external insulating shutters that can be operated from the inside.
These measures added about 5 per cent or 拢3000 to the cost of building a terraced house with a living area of 100 square metres. This extra cost could probably be halved if the techniques were applied throughout the Netherlands. Though Schiedam does not yet demand such ambitious measures for all new dwellings, newly built council dwellings use only 20 per cent as much energy for space heating as their predecessors, built in 1975. Private houses have to meet the same energy efficiency requirements as public sector buildings. The council has banned building materials which it considers harmful to the environment. These include solvent-based paints, window frames made from polyvinyl chloride and many types of wood preservative.
Schiedam is also super-insulating an estate of 450 low-rise flats built in 1956. The project involves adding 150-millimetre-thick slabs of expanded polystyrene to the outside of the solid brick walls, followed by rendering. Insulation is also added to the flat roofs and the floor above the basement. Selectively coated, double-glazed and argon-filled windows are installed, and existing balconies are glazed. New heating systems with mechanical ventilation and heat recovery will complete the improvements that will reduce the gas bill for heating a flat by 80 per cent, from 拢250 to about 拢50 per year.
