I’m sure I’m not the only one who’s been reading in the news that the cost to build the new five-mile M74 motorway extension through Glasgow was £131 million per mile. That’s £80,000 per metre. That’s a lot of money, I hear you thinking, but what’s it got to do with sustainable living? Well, here comes the link…

A recent low-carbon housing fund offered a whopping £170,000 per property, yes, that’s per property, to achieve an 80% reduction in CO2 emissions as set out in the Climate Change (Scotland) Act 2009. This would cover planning the work beforehand and monitoring it afterwards, to make sure it did what it said on the tin, but the lion’s share was to cover the cost of the improvement measures.

As anyone who has ever been involved in a low-carbon retrofit will know, achieving an 80% cut in CO2 emissions from an existing house is extremely difficult. That’s not to say it can’t be done – anything is possible – but the inevitable link is that it's awfully expensive. Unless you’re in a middle-of-the-road, easy to treat house, the insulation, heating and renewable energy generation measures you will need to install will cost you an arm and a leg. Not many of us have that many spare arms and legs these days.

The objective of the fund in question was to build up a portfolio of 50 different house types, showing what measures could be applied to each to achieve the required CO2 cut. That’s all well and good, but there are already enough case studies and pilot projects around for us to know that you can do anything to a building these days … as long as you have the money. The real problem arises when you try and step away from the one-off, pilot project scenario, and ask the question, how do you roll that out to the average householder?

How many houses have we got in the UK? Isn’t it around 27 million? I’m no mathematician, but pick up a calculator and you’ll soon work out that that this clearly isn’t an option. Even scaling this back massively to say £25,000 per property, that would still be an extraordinary total cost. One that not that many people could afford. And the Government isn’t even budgeting for that version, instead going for a nice round £10,000 loan to be made available to householders in 2012 under the Green Deal.

This topic will be covered in more detail as the introduction date looms closer, but there are already a number of questions being asked about the Green Deal set-up. One of these is, how far will £10,000 go towards retrofitting your house (let’s assume it’s a pretty common stone house)? Double glazing and a new boiler? Wall insulation? A biomass boiler? A photovoltaics (PV) system? One of those maybe, but not two and certainly not all. Add on the interest to be paid back, at a rate still to be determined, the fact the loan will have to be sold with the house and the gap between promised and actual fuel bill savings (more on this in the future), and the average householder has a fair bit of soul-searching to do before plumping for that loan. Even so, the M74 cash could have covered over 65,000 Green Deal loans.

It’s clear £10,000 won’t get near an 80% CO2 reduction, which is what we’re told we need to achieve. On the other hand, £170,000 is totally unrealistic. So the question is, if we’re prepared to spend £131 million per mile on a new road, how much are we willing to invest for a more sustainable future?

- Nick