Other standards

Emergency Roof RepairVarious yardsticks of energy performance are used for different purposes. One of the most useful is the NHER (National Home Energy Rating). It is similar to the Standard Assessment Procedure (SAP) referred to in the Building Regulations, but more sophisticated, taking into account local microclimatic factors, how a home is occupied, cooking, lighting and appliances. A low-energy home would score 10 or very nearly 10 on a scale of 1 to 10.

Energy strategy

The first step is to reduce energy consumption by measures that may include:

  • Site layout to provide as much shelter as possible.
  • Planning homes to reduce heat loss by adopting a compact built form and incorporating lobbied entrances.
  • Construction of an airtight, well-insulated building envelope.
  • Systems for heating, hot water and ventilation which are efficient.

It is also important to be aware of how to operate the building and its systems in an energy-efficient manner.

Having reduced the demand for energy as far as possible in these ways, you need to consider replacing energy from fossil fuels with energy from renewable sources. This might include solar space-heating and hot water, solar electricity generation and, depending on where you are, wind power, biomass fuel and other sources of energy. For more detail, please see Renewable Energy (pi68).

Residual fossil fuel use and consequent CO2 emissions can be offset by planting and maintaining trees to absorb CO2, creating a ‘carbon neutral’ development. This is only relevant if emissions have been reduced by all other ways of cutting consumption and replacing fossil fuels with energy from renewable sources. Many environmentalists do not regard ‘carbon sinks’ as sustainable. These issues are considered in more detail under Carbon Offset (pi73).

The costs and benefits of reducing energy consumption

Reducing energy consumption means extra capital costs at the outset, for instance by increasing the amount of insulation. However, if you take a radical

approach and reduce energy use very significantly, you may be able to offset the initial extra cost of insulation by eliminating the need for a central heating system. Furthermore, reducing energy use and fuel costs will save money in the longer term. There may be an opportunity cost for futureproofing your house against future climate change and alternative fuels which may be offset by savings in the future

Reducing energy use:

  • cuts running costs
  • increases comfort
  • can enhance the value of your property
  • reduces global warming, climate change, acid rain and smog.

Summary

Energy conservation is the most important issue from an environmental viewpoint. It may not be easy to improve the performance of an existing building.

  • Reduce energy use by considering site layout, house planning and, most important, constructing a well-insulated and airtight building with efficient systems.
  • Only then consider renewable energy from the sun or wind.
  • It is prudent to consider the future when designing and building in the present. New houses should be ‘future-proofed’ against worsening climatic conditions – more storms, rain, flooding and also drought. Britain will shortly become a net importer of natural gas, and the security of our energy supply is threatened as a result. Build in the possibility of using other fuels.

This section considers how site layout for shelter from the wind and orientation for solar energy can reduce energy consumption.

Microclimate

The relationship of buildings to the local microclimate can reduce the amount of energy required for heating. Shelter from the wind can reduce the amount of heat loss from air leakage, and designing to capture heat from the sun can reduce the amount of heating required. These issues apply largely to new homes, but there may be limited scope to improve shelter around existing buildings.

Shelter

High winds increase infiltration of cold air and also cool the outside surface of the house, especially when it is wet from rain; this increases heat transfer from inside to outside. In Britain generally, over half the wind comes from the south-west. Around another 15% is from the north-east, but wind from this direction is on average 5°C colder. You should design with wind from both these quarters in mind.

Site layout for shelter from wind

When laying out the site, consider:

  • orientating the narrow end of the building to the prevailing wind to reduce exposure •
  • spacing groups of buildings around six times their height apart, to maximize the sheltering effect
  • planting shelterbelts of trees about as high as the building and at a distance from the building of between one and three times the height
  • courtyard layouts, L-shaped plans and walled gardens all create shelter and also pleasant sheltered external space.

Orientation for solar energy

An unimaginable wealth of energy falls on the earth’s surface and provides nearly all the world’s energy needs through warmth, wind, rain and plant growth. The solar energy falling on the earth in one hour is equivalent to our global annual fossil fuel use. A tiny amount of this energy goes into fossil fuel reserves, but we are using these reserves at a much faster rate than they can form. To intercept some of this energy and turn it into useful electricity, hot water or warm buildings is to use the planet’s energy income rather than our dwindling fossil-fuel capital. It is estimated that an effective strategy to use solar energy can provide up to one third of the space heating and one half of the hot-water requirement for a family house. It can also provide up to 70% of the electrical power requirement.

The site layout should provide access to solar energy. The spacing of buildings should prevent overshadowing. Remember that a shadow falling on one cell of a photovoltaic array can reduce its effectiveness enormously. Shading on a solar hot-water panel, on the other hand, is much less critical. The principal elevations of buildings should be orientated within 30° of south. Deciduous trees can be planted to provide shade in summer to prevent overheating of south-facing rooms and conservatories. When the leaves drop in winter, daylight and sunlight will be admitted, although it is important not to plant too densely or too close to the building or there will be too much shading in winter.

Costs and benefits

Low-energy dwellings are likely to increase their value as energy becomes more expensive and people become more aware of energy use in houses.

Summary: designing with the site in mind to reduce energy consumption:

  • Lay out the site to maximize shelter from the wind.
  • Orientate buildings to maximize the opportunities for solar energy.

House Planning

Having looked at how the site is laid out, this

section deals with the planning of the home itself to

reduce energy consumption.

Form

The form of a house can reduce heat loss in several ways, as follows:

  • Reduce the exposed external surface by avoiding detached houses and by designing as compact a form as possible. For example, most flats have only the front and back wall exposed.
  • Reduce the area exposed to cold winds by having a low roof on the north-east side.
  • Sheltering the building with earth can achieve a similar result.
  • Planting climbing plants so that they cover the walls will tend to extend the boundary layer of warmer, less turbulent air around the building and reduce heat loss.
  • Deep roof overhangs help. They also shelter the walls from rain.

Above: The low roof at the back of this cottage in Norfolk protects it from the north-east wind.

Below: Climbing plants provide shelter and reduce the cooling effect of the wind, especially when it is wet.

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