The bright future of eco-homes
Thursday, 22 May 2008 12:00 AM
With the irresistible rise of eco-homes underway, Ian Moores examines how modern architecture can contribute to the battle against climate change.
Eco-homes are now firmly on the agenda of everyone concerned with housing. The government is planning to build ten eco-towns as part of a drive to construct three million new homes - but how will they function, and how will housebuilders construct the perfect eco-friendly property?
The idea of developing new housing which can respond to the ever growing demand for carbon neutrality really is here to stay, even if there is still scepticism over economic viability and how far it is possible to go.
In the past a green home was very often a lifestyle choice of those who advocated a return to nature, however, the growing long term uncertainty about fuel supply and rising costs means the drive towards sustainability is now officially mainstream.
Gordon Brown's eco-town challenge set out the possibility of extensions to existing towns or new urban settlements of approximately 10,000 - 20,000 dwellings, where the issues could be tackled in a holistic way. Undoubtedly, this would appear to offer greater opportunity to deliver real improvement across the board, but how realistic are eco-towns in shaping the future?
It is likely that eco-homes will actually be constructed as part of the existing built environment, so how will housing evolve? And how do we specifically define an 'eco-home'?
The government's own strategy centres on the Code for Sustainable homes (CFSH) - which is a staged approach to reaching zero carbon housing.
Introduced a year ago the CFSH is fast becoming a landmark on the horizon for private developers and the central focus of those working in the public sector.
For private speculative housing production there is still no mandatory compulsion to undertake a Code Assessment, although from April 2008 a rating is mandatory (even if an assessment has not been carried out). Currently all social housing projects funded by Housing Corporation grants need to achieve level three of the Code (code levels range from one - six with code six being true zero carbon). Currently many Local Planning Authorities (LPAs) are already imposing CFSH level three on all new residential development.
Central government have set a target for all new homes to be carbon neutral by 2016.
Building a green home has increasingly become a matter of reducing the amount of greenhouses gases (primarily carbon dioxide) used in its construction and subsequent use.
So if you actually want to build yourself a green home how do you go about it?
There are two things to consider, firstly the amount of carbon which the completed house will release in its operation through the need for heating, lighting, hot water requirements and potable water use. Secondly, the amount of carbon used in its actual construction (for instance firing of clay bricks for facing brickwork). These two components represent the primary impact that the house will have on the environment.
You may question where the addition of new technologies to generate heat and electricity come in. Wind turbines on the roof certainly advertise your green credentials, but if you are loosing all your heat through gaps in the windows and doors any benefit will be lost.
Start looking at reducing the energy used before considering renewable energy.
The house should be as airtight and well insulated as possible. It is difficult to consistently achieve good air tightness with traditional brick and block construction, instead various new constructional systems can be employed which help reduce the leaks to very low levels. Manufacturers are currently all clamouring for a share of this huge emerging market. There are interlocking pre fabricated timber panels, insitu concrete walls and blocks which are bonded with adhesive mortar. These systems also permit essential high levels of insulation, which greatly exceed current Building Regulation standards. Such airtight construction would ideally use mechanical ventilation systems which can extract the heat from stale air and use it to warm fresh air from outside.
Typically these techniques combined can reduce the energy used in heating by 75 per cent. In Europe many homes have been built to this standard and the heat generated by the occupants mean that is some cases no heating is required.
When designing the house the final orientation is critical in order to maximise the amount of solar heat collected during the heating season.
Generally the house should be planned to ensure the main living rooms have a southerly aspect with glazing to collect warmth from winter sunlight. This is a potential challenge in layout planning because other design considerations often dictate that a south facing house cannot be accommodated. However, once there is an understanding of the need to bring winter sun into the main living areas there is a lot which can be done, even if the design is unable to achieve the optimum orientation. Very often a 'sunspace' is employed, which is effectively a greenhouse to trap warmth from the sun. Windows which face north should be limited to smaller openings.
Hot water and lighting energy requirements can be effectively reduced by efficient water storage and low energy fittings respectively. Reducing the water used in operation can be achieved by careful selection of fittings; in addition greywater recycling and rainwater harvesting help reduce the requirements for treated potable water supply to the house.
Ventilation strategies are essential to maintain a pleasant and healthy air quality in the dwelling when high levels of air tightness are achieved.
The energy used in manufacturing the building materials should be reviewed carefully as it will contribute to the carbon footprint of the completed house.
Once the basic fabric of the building is right and the energy requirements as low as possible, the options to implement renewable energy options open up. Theoretically it is possible to generate the total energy requirements of the house on site if enough renewable sources are included. Although, the high cost of the current technology suggests that it is still not economically feasible. Current technology includes sources such as solar thermal panels, wind turbines and ground source heat pumps.
There are only a few example zero carbon houses in the UK, if zero carbon is taken to include the carbon footprint of the house in use (including energy used in powering appliances). To physically generate the full heat and power requirements of a house is massively challenging, particularly in a dense urban environment, even if the cost of renewable energy components were not taken into account.
Ian Moores represents Ark Design & Architecture - www.arkitecture.co.uk - CFSH and SAP assessors with wide-ranging experience in both public and private housing.
