How do we build a green extension?

'Dwelling envelope' is by far my favourite term of the week, used liberally in lieu of 'house' in the latest research papers on sustainable building. Upsizing your 'dwelling envelope' in a non-sustainable way would mean another significant contribution to the building sector's 33 per cent share of man-made global emissions. A low-carbon extension won't completely negate your impact (unless you are a very brilliant eco builder), but experts insist homes could achieve a 60-70 per cent reduction in CO2 emissions with 'plausible combinations of existing and/or emerging technologies'.
But decarbonising our living space is partly dependent on scaling back energy consumption. So while nobody will expect you to enjoy your new room sitting in the dark, hold back on the gadgets and halogen bulbs and remember that compact fluorescent lamps provide four to five times the lumens per watt of the incandescent variety.
Talk of fixtures and fittings is, however, a bit previous, because first you need to build the thing. You should have high aims. All new homes are supposed to conform to those set by the PassivHaus system by 2013, and be zero carbon by 2016 (passivhaus.org.uk).

You can start now. While you should not expect to find fleets of eco builders waiting to chat through plans for a straw bale extension, the Sustainable Building Association (aecb.net) may put you in touch with one or two. If your extension is of the DIY variety, the Centre for Alternative Technology runs a wide variety of courses (cat.org.uk).

A more mainstream route is to buy a timber-framed extension, as long as the company can prove the wood is from a renewable and sustainable source (English Heritage Buildings, at ehbp.com, specialises in renewable English green oak). A timber structure built instead of a masonry home saves about four tonnes of CO2.

But timber is far from the complete solution - and on a massive scale it would be unsustainable. Neither is it the only way of 'decarbonising' your home. The Building Services Research and Information Association suggests vacuum insulation panels (wacker.com)), daylighting systems and controls (daylightsystems.com) and photovoltaic and solar thermal systems (solarcentury.co.uk).

Begin with an online trip to the Green Building Store (www.greenbuildingstore.co.uk) and order your insulation pronto. The word on the street is that European manufacturers are struggling to keep up with demand.

Will it be worth it? Well, according to the Commission for Architecture and the Built environment (cabe.org.uk) 84 per cent of buyers would pay an extra two per cent on the purchase price for an eco-friendly home. You can expect some fiscal gain for pushing that green dwelling envelope.

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