Whether you are already a self-builder or you have aspirations to be one in the near future, you will already be aware of the new government initiative to make all new homes Carbon neutral by 2016. As of May 2008 all new domestic buildings must comply with the Code for Sustainable Homes (CSH). The CSH was designed to provide a comprehensive measure for the sustainability of new homes through the assessment of their performance as a whole. Since April 2008 it has been a legal requirement for new homes to have an Energy Performance Certificate quantifying its energy efficiency. Local planning authorities are already getting to grips with the CHS and, although they have no legal power to apply it at this time they will certainly be more sympathetic to a dwelling designed with this in mind. In any event it will not be long before it is legally enforceable.

Intelligent, thoughtful design
The CSH is a complex affair that sets the standards for assessment of new homes and is really only for the enthusiast. For those of you who only want a working knowledge of it and its impact on the design and specification of a new design I have attempted to provide a simple and useful interpretation that should be used as a tool for the design of a new home. It will soon become clear that the notion of choosing a standard or existing design e.g. those from a kit company's pattern book, is not going to address the issue of sustainability. A well-designed house is not a kit of parts selected from a menu, it is the product of careful consideration of many aspects including those mentioned in the following pages. I have dealt with the major factors under six headings. These are emissions, water efficiency, surface water, sustainable materials, the environment/biodiversity and waste management.

1. Emissions

The Intergovernmental Panel on Climate Change (IPCC) has predicted a rise in global temperatures between 1.1C and 6.4C by the end of this century. The likely effects of this have been well publicised and form the reason for our commitment on national emissions. As housing represents a quarter of these emissions the commitment to zero Carbon by 2016 can be understood.

1.1 Passive Solar Design

Orientation, shading, thermal mass, ventilation and air-tightness and the design of windows all have an impact on a house's energy demand. Passive Solar Design should exploit the free energy from the sun for heat and light. The objective is to make most use of solar energy for heating in the winter whilst avoiding the need to cool the house in the summer. The exploitation of free light is also central to the design. Well-designed homes can expect up to 10% energy savings from this alone. To achieve this benefit a house should keep most of its windows and patio doors facing south, within 30degs. Once you have maximised the amount of solar energy entering the house it is important to retain it and this is done by using materials with mass such as those found in modern brick & block houses. To avoid overheating in the summer some means of shading is required and this can be by means of shading devices as part of the building fabric or tree planting strategically placed near the house. To achieve high levels of air-tightness to avoid heat losses it is important to design in high levels of insulation and this includes the junctions between different parts of the structure. Ventilation is still required for well being but this should be by natural means if possible and certainly controllable.

1.2 Energy efficiency

The CSH is specifically interested in the efficiency of appliances using electricity. That covers everything from energy saving lights to white goods. Renewable energy however is significant but should not be used in isolation but along with measures to reduce the house's energy demand and increase its energy efficiency.

1.2.1 - Solar collectors are less efficient in the UK than in Mediterranean but they still have a part to play in providing renewable energy. They work best on a south facing roof that is relatively steep. Don't expect water from these collectors to be very hot. As regards photovoltaic collectors these provide electricity but are relatively expensive at this time.

1.2.2 - Biomass boilers are designed to burn agricultural and forestry waste products. The fuel comes in the form of simple wood chip pellets. These boilers have a relatively short payback period but they do require provision for storing the relatively bulky fuel. It is also important to research the supply chain to ensure a cheap and reliable source.

1.2.3 - Heat pumps are all the rage at the moment with claims of efficiencies up to 350%. These claims may be achievable if the pump is a ground or water source and is employed in running underfloor heating. Air source pumps are generally cheaper to install but care is needed in deciding upon their location.

1.2.4 - Double-glazing is the current standard under the Building Regulations. As the glazing in your windows and doors is the most vulnerable to heat loss you may wish to consider triple glazing. Particularly as modern designs are including greater areas of glazing to maximise natural light and solar gain. This brings the 'U' value of the glazed units down to 1.0 w/m2/°C and it is not so many years ago that that was the requirement for insulated cavity walls! So you can see how significantly the regulations have moved on.

1.2.5 - Wind turbines are not enjoying good press as their outputs per pound sterling spent on buying them is very poor. They are also affected by their location. As you can imagine a hilltop plot works best!

2 Water efficiency
With all new homes required to have mains water metered there is a clear and direct link to your pocket. Two means of keeping costs and environmental impact down are to harvest rainwater and to efficiently use what you pay for. More efficient ways to use water are to specify spray or low-flow taps, dual-flush toilets, A-rated white goods and use showers rather than baths.

Rainwater can be harvested for flushing toilets, garden irrigation and washing cars. In addition to rainwater you can install grey water systems that filter and sterilise wastewater from showers and baths for the same purposes as rainwater. Even rainwater butts earn points in the CSH.

Consider using plants with a low water demand in your landscaping scheme.

3 Surface water
Recent serious floods in Carlisle and the rivers Don and Severn have highlighted the need to control the dissipation of high intensities of rainwater. In recent years the situation has been exacerbated by the use of impervious landscaping to new residential developments. The appropriate measures will depend upon the geographical location of the plot but the most common measures are Sustainable Drainage Systems (SUDS). These range from simple filter strips and swales to permeable hard finishes to parking and patio areas. It is worth mentioning that green roofs such as Sedum actively reduce the sudden discharge of rainwater.

4 Sustainable materials
Significant quantities of energy are bound up in manufacturing (and ultimate disposal) of building materials. This points to the need to a responsible specification and it is important to consider all aspects of environmental impact. These are the materials lifecycle, undesirable by-products, site waste and recycling

4.1 The lifecycle of a material is about its environmental impact over its useful life.

4.2 By-products from the material include both pollutants created in its manufacture, its disposal and any by-products it might discharge directly to the environment.

4.3 Building sites are terrible places for waste so it is important to avoid supplying an excess to site. It is important to ensure that there is sufficient to allow for unavoidable waste. This is called 'overage' and is an accepted part of good site management. Careful selection of builder and supplier can have a significant impact on unnecessary waste and expense. Recycling comes under this banner inasmuch as any reused materials will contribute to a sustainable home.

5 Biodiversity
All building plots come with their own unique biodiversity. In urban areas this may be small but should still be given careful consideration. There is more wildlife in towns and cities that you may actually see. In rural locations the biodiversity may also include trees, ponds, drainage ditches and the like. Any measures to retain these features contribute to the sustainability of your new home, enhancing it will be even better.

6 Waste management
I have already mentioned waste during the construction of your new home as well as the measures to minimise it. Waste is also an environmental issue during the life of the house. The code seeks to encourage actions to minimise waste followed by measures taken to re-use and recycle, composting organic material, recovering energy before disposal.

Conclusion
The old adage that choice is the very essence of self-build is particularly appropriate when considering how self sustaining, low carbon and 'green' you want your new home to be. By using good design and careful selection of materials you can build an energy efficient home within the current regulations. And perhaps more importantly within the recognised average build cost bands. If your conscience is telling you to build 'greener' or you want to invest in higher levels of self sustainability or both, then building your own home offers you that unique opportunity. These choices will have costs attached to them - you should ensure that you are in full control of these and be able to make informed decisions.

Tom Somerville BA (Hons) ARIAS
Chartered Architect