When trying to assess how green your home is, the first thing to consider is its age. Energy-efficient construction practices have improved over the years, helped along by tightening building regulations and better insulation products. As a result, any UK home built post-2001 should require little or nothing in the way of retrofitting. The walls, loft and floor will already be fairly well insulated, the windows will have modern double-glazing and the boiler should be reasonably efficient.
It's possible to make a typical modern home even warmer, of course, but the benefits of adding yet more insulation will be small compared to the level of cost and disruption involved, so you might be better focusing on reducing your electricity usage rather than trying to reducing your heating bills.
At the other end of the spectrum are homes built in or before the early 20th century. Whereas a typical-sized house from the turn of the millennium might have an annual carbon footprint of four tonnes, an unimproved Victorian or Edwardian equivalent with no wall insulation, open fireplaces and single-glazed windows would use much more energy and create roughly twice as much CO2. In these older homes, heating and insulation are the crucial areas to focus on. Appliances and lighting will be worth improving too, of course, but heating will constitute the majority of the home's energy bills and emissions.
Another key factor in determining the leakiness of a home is the number of external walls it has. This is important because external walls, and their windows, are responsible for around half the heat loss in a typical home.
By contrast, party walls – those shared with neighbouring homes – are generally not a problem, because heat flows in both directions. Hence flats and terraced houses with two or more shared walls tend to be relatively efficient compared to detached, semi-detached and end-of-terrace homes.
It's not just the number of external walls you have that counts, of course, but what they're made of and whether they've been insulated.
The first thing to check is whether you have solid walls or more efficient cavity walls (made from two thin walls separated by a gap). One way to tell is the age of your property: any post-1930 home is likely to have cavity walls, while anything earlier probably has solid walls. The pattern of the brickwork is another good clue. If all the bricks are laid lengthways on then you almost certainly have cavity walls; if the length-ways bricks alternate with bricks laid sideways on, then you probably have solid walls.
Cavity walls are good news, but you'll need to check whether the cavity has already been filled with an insulating material. Inch-wide filled holes on the exterior of the walls can be a clue that the walls have already been injected with insulation material, though to be sure you might want to call in a local insulation company.
If you have solid walls, then it's relatively unlikely that they will have been insulated already, though a builder or insulation firm should be able to confirm. You can have insulation added, though it will be more expensive and a bigger upheaval than it is for cavity walls, especially if you're in a conservation area, which will usually mean putting the insulation on the inside of the walls, eating into your floor space.
As well as the walls themselves, you'll need to consider the windows they contain. Anything single-glazed will be pushing up your energy bills by leaking heat to the outside world – especially if you have old frames with drafty gaps around the panes. The material of the frames makes a difference, too: metal is more thermally conductive than PVC or wood, so it increases heat loss.
Once you've sussed out your walls and windows, consider what's above you. Assuming it's a loft rather than a flat, check out how much insulation you have up there. Anything less than 10cm is an energy disaster, while 20cm is a sensible minimum level.
Last but not least, consider your boiler. Anything 10 or more years old is likely to be so wasteful with fuel that it's worth considering upgrading to a modern condensing model. You can check the efficiency of your current model at the Boiler Efficiency Database (sedbuk.com).
If you'd like a more detailed understanding of the energy efficiency of your home, there are various virtual and real-world services that might be of interest. But before you try those, first make sure that your home hasn't already been subject to a green inspection. If you live in a property that you purchased in the last year or so, then the seller should have provided you with an Energy Performance Certificate (EPC).
This document will rate your home from A (best) to G (worst) for energy efficiency and CO2 emissions. Based on a visit by an energy assessment company, an EPC will also list a number of measures that you could consider to reduce your bills and carbon footprint.
If you've never had an EPC for your home, or you can't locate your existing one, then you can get something similar by taking a free Home Energy Check on the website of the Energy Saving Trust (energysavingtrust.org.uk). Answer 20 or so questions about the type of home you live in, your heating system and so on, and the site will create a report for you.
The Energy Saving Trust also operates a freephone helpline (0800 512 012) that will advise you on all aspects of assessing and improving your home's energy efficiency.
Questionnaires and helplines can only tell you so much, however. If you're really serious about greening your home, there's no substitute for having an expert come to inspect the property and give you some detailed advice – right down to particular models of lightbulb and recommended builders in your area. Some of these home-energy assessment services will even test the leakiness of your home by temporarily increasing the air pressure inside and seeing how quickly the extra air leaks out.
One ambitious home energy assessment scheme is London's Green Homes Concierge service, which offers a detailed home energy audit for a one-off fee of £199. Similar schemes exist elsewhere in the country: try the Energy Saving Trust helpline to find services in your area, or check with your local council, which may offer free or discounted home assessments.
Alternatively, for advice on a specific element of your home's energy performance – such as insulation or windows – you could try getting the opinion of relevant local companies and tradespeople. A good way to track them down is via their trade associations, such as the National Insulation Association (nationalinsulationassociation.org.uk) or the Glass and Glazing Federation (ggf.co.uk). Or, for really ambitious projects, locate an environmentally conscious architect via the Sustainable Building Association (aecb.net).
CHECK YOUR BILLS
Roughly speaking, the higher your energy bills, the bigger your home's carbon footprint and the greater the benefits of investing in green improvements. For reference, the typical home on the gas network currently spends around £450 per year on electricity and £700 per year on gas. That works out as £16 per person per month on electricity and £24 per person per month on gas. If you're spending much more than that, then it's likely your home could be particularly well suited to some energy-saving measures.
OIL, ELECTRIC AND SOLID-FUEL HEATING
A small but significant proportion of UK homes are not connected to the gas network and rely on oil, electricity or solid fuels for heating, hot water and cooking. These homes tend to have particularly large carbon footprints, because the fuels they use are more polluting than gas.
Whereas mains gas creates 185 grams of CO2 for each unit of heat created, oil releases 282 grams, coal releases 330 grams and electricity releases a massive 537 grams. In other words, heating your home or water with electricity will typically cause almost three times more global warming than using a modern gas boiler.
As well as being polluting, oil, electricity and solid fuels are also expensive ways to create heat. If you rely on these fuels, then, your home may be particularly suitable for green improvements such as better insulation, double glazing and a wood-based heating system.
