Energy efficiency used to be easy. “Put more insulation in,” we used to advise. “Fit a condensing boiler.” Or maybe “fit the best glazing you can afford.” And always “more insulation — it’ll keep paying for itself over and over again.”

But then the Building Regulations caught up. By 2006, minimum insulation levels were somewhat above what they had been even in our 1990s eco houses. Condensing boilers had become mandatory and the minimum glazing standards were now better than what we had once considered ‘high performance’.

However, it seems our techno-fix solutions may be running out of legs. Insulation in particular is subject to the law of diminishing returns. This means that whilst the first inch of insulation saves a huge amount of heat, the second and third saves rather less, and so on. By the time you’ve got to ten inches or more, it’s beginning to make very little difference. In fact, the difference between the tenth and eleventh inch is dwarfed by other factors, notably airtightness. If your heated space isn’t free of draughts, then all that added insulation will make no difference, because the heat will just seep out of the house through the holes. You simply can’t build a really low-energy house without addressing this issue of airtightness — it’s critical.

People living in Canada and Scandinavia know all about airtightness. They know all about it because when it gets to -25°C outside, you get cold. Real cold. You don’t sleep with the windows open in winter in Montreal or Uppsala. You learn to build airtight. In fact, Canadian experience suggests that you can build low-energy homes with no more insulation than we already use in Britain, provided you make the houses airtight.

But for an airtight house to work, you have to manage the air itself. The key is to fit a mechanical ventilation system, just as you would in an office or on an airplane. There is no doubt this strategy works. There are numerous examples from across the world, including some in the UK, which show that we can construct houses which are really comfortable to live in with minimal spaceheating requirements, by balancing the correct combination of good insulation and airtightness, combined with a whole-house ventilation system.

The problem is that here in Blighty, we like our fresh air. In fact, many of us even like our homes to be a little draughty. We associate airtight homes with being stale, humid and, sometimes, even unhealthy — fearing outbreaks of mould and damp if there isn’t enough ventilation.

This problem is more cultural than technological. Airtightness is key to building a really low-energy home, but where’s the cat flap going to go? There’s no place for a draughty letter box or for rattling windows. And there’s definitely no room for an open fireplace. Everything has to be sealed like peas in a pod if you want to get an airtight house to work for you. If you simply stick a mechanical ventilation system in a leaky house, then you end up double-ventilating. The mechanical system whirrs away in your loft doing the best it can, whilst your house goes on self-ventilating, just as it always has done. That’s not energy efficient — quite the reverse, in fact.

You see, to achieve a low-energy house you have to understand the principles involved. And you have to be prepared to adapt your lifestyle, learning to live in your house the correct way. Or, to put it another way, you have to learn to drive your home like you drive your car. Just as your car’s fuel consumption depends to a large extent on how you drive, so your home’s energy performance depends on how you live in it.

So the decision facing our policy makers now is whether to go on adding yet more insulation and further emphasising airtightness, or to hold off and admit that they are wasting their time in pursuit of standards which will never be met in practice, unless or until there is a substantial financial penalty involved.

With domestic fuel still taxed at just 5% and winter temperatures rarely going much below zero, there simply isn’t that much of an incentive for us to adopt Swedish or Canadian lifestyles. And there is a real danger that we will be building to much higher standards of energy efficiency, but that this won’t translate into lower fuel bills or reduced carbon emissions — because we don’t like closing our windows.


  • DavidLerner

    And there was I hoping you’ve give us the answer to the catflap problem which is one I am grappling with right now! Letterboxes are easy to deal with, a porch, an external box, a sealed box on the inside, etc. But a catflap? The cat wont cope with inner and outer doors, it wont want a flap in a thick cavity wall but one wouldnt want to put it through the expensive sliding doulbe/triple glazed doors, and I cant find a flap that is really draught proof. Any ideas, other than give the cat away?

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