If you had a few thousand pounds to spend on your house, what would you do with it? Would you build a new double garage, with an office and a playroom over? Would you go down the traditional route and build a beautiful, really well designed conservatory? Or opt for a new and bang up to date bathroom, or – the 21st century favourite – a home cinema (sorry, media room)!

They’re all lovely ideas – and it wouldn’t be hard to come up with another dozen or so – but if we’re really up to date with modern thinking then the answer might be very different …

Green is of course the new black. We are all being exhorted to do our bit for climate change by not leaving our TVs and DVDs on stand-by, by fitting low energy light bulbs throughout the house, and by turning our central heating thermostats down a degree or two. The next step should be to go as far as possible in making our homes energy efficient, we’re told - and that can cost very large sums of money. The question is; is it worth it? Do ‘green’ measures really save money over the average length of home ownership?

There is, as Conrad Payne of property specialists Strutt & Parker says, no one answer; ‘Energy efficiency does cost money, but looking at the bigger picture can you put a price on it? At some point someone does have to put their money on the table if we want to reduce energy waste.’

The government has really tightened up the regulations for new houses. By 2010 carbon emissions from a newly built home must be down by 25% from the present figure – and right down to zero by 2016.

Some solutions are simple and inexpensive. Efficiently collecting rainwater off the roof, both for use in the garden and as ‘grey water’ to use in flushing the WC, makes a lot of sense and need not cost a lot.

Just about everything else on the eco-agenda requires a considerable investment though, and it’s difficult to know how long – if ever – it will take for the installations to pay for themselves.

The fact that you can generate energy from solar panels is well known, and the technology has been around for about 25 years. It was prohibitively expensive, but costs have tumbled over the past five years or so. Even in this country we get enough sunshine for a solar system to generate between a half and three quarters of a house’s energy.

You can go solar for between two and four thousand pounds, but if you want a geothermal heating system it could cost you as much as £50,000. These draw warmth from the earth, either from a deep bore hole or a network of pipes lying just below the surface of a large area such as a lawn. A geothermal system can cut your heating bills to 25% of what they were, but you need to do the maths very carefully to see if it’s going to be worthwhile for you. What if you get a great job offer six months after installation and need to move?

Experts are less keen on wind turbines, which have had a lot of publicity recently. Planning consent has to be obtained before they can be installed (that’s true of solar panels too), and they may not be popular with your neighbours. They will make only a small contribution but as the technology brings the price down they might become more worthwhile.

As Michael Fiddes – who is based at Strutt & Parker’s London office - points out, ‘From June anyone selling a home will need to compile a Home Information Pack, and one element in that will be the energy efficiency of the house. An inspector will assess your home and give you a certificate with a rating on a scale from A to G – much as you find already when you’re buying a domestic appliance.

‘This is something of a blunt instrument though. Obviously older and larger houses will tend to fare less well than smaller, more modern homes. A three bedroom terraced house built in the last couple of years, under current building regulations, will have a better rating than an 18th century former rectory – but anyone with their heart set on an early Georgian vicarage isn’t going to be put off for a moment.’

Such a house is unlikely to have double glazing (not least because it is going to be Listed!) but it will almost certainly have a well-insulated roof space. These two energy-saving measures have been around for longest, and can be found in the majority of homes. Insulating a roof is not expensive, and grants are available to cut the cost even further, but if you live in a house for as long as twenty years you might not recover the cost of double glazing from savings in your heating bills.

‘It is true to say that in all of these areas the technology is getting better and better, and prices are coming down. Central heating boilers are smaller and more efficient than ever, and under floor heating – which was inefficient and very expensive twenty years ago – is now a very good bet.

’It’s certainly true to say that home-owners are becoming ever more aware of the desirability of reducing energy costs, and – looking at the bigger picture – of the need to do their bit to combat climate change.’