Do you ever wake up in the night to discover that your partner (or pet cat) has stolen most of the duvet and your uncovered feet feel like they've frozen solid? Imagine going to sleep without any blanket or sheet to cover you. Brrr. If you could get a thin blanket, that would be an improvement over nothing at all. But if you could get a really thick down-filled duvet instead, mmm, you'd be cosy and snug all night.
That's what loft insulation does to your house. Without any insulation at all 15% of your heating costs (about £110 per year)could go straight through the roof. If you have a little bit of loft insulation, say up to about 50mm (2 inches) that would be a lot better than nothing. But if you had a really thick layer of loft insulation, say up to 270mm (about 10 or 11 inches), then every bit of heat stays in your house where you want it, your bills come down, and so does your carbon footprint, by around 1 tonne of CO2 per year.
That's why I climbed up into my loft armed with a ruler, a torch and a camera (you probably don't need the camera) to see how much loft insulation I have. It turns out there's about 80mm up there (just over 3 inches). That's better than nothing, but not really enough.
Since space heating and water heating account for a whopping 84% of our typical household energy consumption, topping up my loft insulation is perhaps the single most significant thing I can do to bring down my energy bills and my carbon footprint. It puts low-energy lightbulbs in the shade. However it's a bit more costly and time consuming than simply buying a different type of bulb whenever one goes "ping". Topping up your loft insulation costs around £200 if you do-it-yourself (maybe £500 if you GALMI - Get A Little Man In). But you'll save the DIY cost in under 2 years of reduced heating bills (less than 5 years for the GALMI version). There may also be grants available. I'll be looking into that over the next few days - if anyone knows anything about loft insulation grants, please drop me an email.
It takes about half a day to insulate your loft, but perhaps more if your loft is full of junk which will have to be removed first. I don't know what the insulating value is of boxes full of old clothes, books and unused sporting goods. I wouldn't rely on it myself.
Do you know how much loft insulation you have? Go and have a look, and then you can click "I've done one thing on the list!" in the poll in the right-hand-sidebar. If you need to add more insulation and you do so, you can click it again.