How to Build a Sustainable Home

ABOVE: A zero-carbon self-build employs an innovative method of passive cooling and heating - Architect Richard Hawkes’ self-built zero-carbon home in Kent is built using thin lightweight clay bricks, using a system known as timbrel vaulting. The 9m-tall and 22m-wide vaulted arch is built from four layers of tiles yet is less than 125mm thick and topped with 80 tonnes of planted soil and gravel.

If you are planning to build your own home and intend to live in it for several years, it makes sense to think about future running costs, especially energy consumption — but just how far do you take this idea? It is possible to build a zeroenergy house, or even a house that is a net energy exporter, but the capital investment required is likely to outstrip any economic benefits – at least in the short term – so the incentive would have to be saving the planet rather than saving money.

New developments in microgeneration and renewables hold great promise, but once you start investigating the cost and payback of such technology it quickly becomes clear that these features cannot be viewed in isolation, and that it makes more sense to look at energy conservation first, by designing and building a home that consumes as little energy as possible.

Sustainable Design

There are a growing number of house designers specialising in sustainable home design and each of them takes a slightly different approach. Cost quickly becomes the major consideration: do you invest in building a hi-tech ‘PassivHaus’ with super insulation that requires little or no central heating, with all of the inherent effects on the appearance, siting and orientation of the property that this may entail, or do you go ‘low-tech’ and build a house using local, natural materials, which may not achieve the same levels of insulation and airtightness, but has very little embodied energy and so may be greener over its lifespan?

A third option is to divorce the two aspects of design and construction and to take a more pragmatic approach, creating the home you really want in terms of appearance and specification, and to then mitigate this as far as practical, and affordable, by using sustainable materials and reducing water and energy consumption.

For most self-builders, the latter may be the most realistic approach, especially when it comes to getting planning permission and maximising future resale value.

Whichever route you take, there is still the option to add renewables, just as there is to an existing property, including solar panels, a heat pump, wind or water turbines, photovoltaic (PV) panels and water conservation features such as rainwater harvesting or greywater recycling.

The Current Rules

Relative to just a few years ago, all new houses are now inherently more sustainable as the Building Regulations drive forward the standards of sustainable design and construction. The currently voluntary Code for Sustainable Homes (communities.gov.uk/thecode) sets out the way forward for the Regulations and these measures, expected to become mandatory by 2016, can be adopted now.

As a self-builder, there is much more you can do to reduce the environmental impact of your new home and it need not add significantly to the cost. As with all aspects of self-build, the choice as to how far to take things is entirely your own. Here, we set out the fundamental principles of sustainable home design and you can mix and match whatever suits you, your aspirations and your budget.

ABOVE: The generous insulated cavity and an inner skin of dense concrete blockwork complete the extremely thick external walls in this self-build, and their high thermal mass helps to regulate the temperature of the rooms. (Read more about this self-build).

How To Follow The Code

The Code for Sustainable Homes is currently voluntary but sets out the future direction of the Building Regulations and is projected to become the mandatory standard for all new homes by 2016. It awards new homes a star rating from 1 to 6, based on their performance against nine sustainability criteria (download full details at planningportal.gov.uk).

One star is entry level above Building Regulations, and six stars is the highest, reflecting exemplary developments in terms of sustainability.

• The sustainability criteria by which new homes are measured are:

• Energy and CO2 Emissions: Operational energy and resulting emissions of carbon dioxide to the atmosphere

• Water: The consumption of potable water from the public supply systems or other ground water resources

• Materials: The environmental impact of construction materials for key construction elements

• Surface Water Run-off: The change in surface water run-off patterns as a result of the development

• Waste: Waste generated as a result of the construction process, and facilities encouraging recycling of domestic waste in the home

• Pollution: Pollution resulting from the operation of the dwelling

• Health and Well-being: The effects that the dwelling’s design and indoor environment has on its occupants
• Management: Steps that have been taken to allow good management of the environmental impacts of the construction and operation of the home

• Ecology: The impact on the local ecosystem, biodiversity and land use 

Ecological Construction

The building shell should be highly insulated and built to be airtight, whatever form of construction is chosen. It is considered to be easier to achieve airtightness using modular forms of construction such as timber frame, structural insulated panels (SIPs) or insulated concrete forms (ICFs). Systems using sustainable materials such as timber, laminated timber and natural insulation such as cellulose are most favoured.

Masonry houses can be super insulated and made airtight. It is easier to achieve air - tightness when the walls are wet plastered rather than dry-lined, and where the floor is screeded and the loft space habitable.

Open chimneys are not an option, but solid fuel stoves with a balanced flue are ideal.

Engineered or Natural?

Maximum Renewables

One approach to creating a sustainable home is to create a super-insulated, airtight house with no thermal bridging using lightweight construction, with very little space heating requirement.

Space heating and domestic hot water is provided using renewable technology such as an air- or ground-source heat pump, and active solar panels, and ventilation via a whole-house mechanical ventilation system with heat recovery.

The materials used may have a relatively high-embodied energy, especially the technology, but this can be offset by large savings in energy consumption and possibly export of electricity to the Grid.

This is an expensive approach likely to cost
£2-3,000/m².

Alternative Construction

Another approach is to build using the lowest possible embodied energy by using natural locally sourced materials (cob, oak frame, straw bales, hemp, rush matting, mud bricks) and reclaimed materials, plus passive ventilation. The building won’t be as well insulated or airtight, but may have a lower overall environmental impact in its lifespan. The heat requirement may be met by a small gas condensing boiler for underfloor heating and domestic hot water.

A simple traditional cottage built from cob or timber frame, with a slate, stone or thatched roof and modest timber windows may cost as little as £900-1,400/m².

Hi-Tech vs Low-Tech — Two Approaches

This SIPs-built house (ABOVE) is airtight, requiring a whole-house ventilation system.(Read more about this self-build).

Large amounts of glazing maximise passive solar gain, while additional heat demand is met by underfloor heating powered by a ground-source heat pump; photovoltaic (PV) solar panels generate electricity. In stark contrast, this cob-built house (BELOW) is rendered in lime, floored with earth and insulated with recycled newspaper. Thermal solar panels do, however, provide hot water.(Read more about this self-build).

Different Eco Schools

Zero Carbon

UK Potton’s Lighthouse in Watford was Britain’s first zero-carbon house, meeting Level 6 of the Code for Sustainable Homes, with which all new homes in Britain will have to comply by 2016.

PassivHaus, Germany

The world’s leading standard scheme for energy-efficient construction. A PassivHaus is built so airtight that it does not need a traditional heating system or active cooling.

Super E®, Canada

Takes a holistic approach to sustainability, and requires a wellinsulated wall design, superior construction techniques, high-performance windows and continuous whole-house ventilation.

Further Reading:

• How to Build a Sustainable Home: Design Solutions 
• How to Build a Sustainable Home: Designer's View
• A Sustainable Self Build in Devon

	The H&R Book of Green Homes offers practical advice on how to approach building an eco home, an A-Z of green building and more than 29 in-depth case studies of environmentally-friendly self-build homes.
	Simply Sustainable Homes - This book offers simple, but not simplistic, advice and information for both renovators and builders. It provides a no-nonsense guide to anyone wishing to build their own home or upgrade an existing house in a sustainable way.