The concept of insulating our dwellings against the cold is hardly a new one – the nomads of the Central Asian steppes have been wrapping their yurts in fleeces and felt for millennia – but unfortunately the era of cheap North Sea oil has meant that here in the UK we are still lagging behind our European neighbours in all things thermal (pun intended).
Thermal insulation is important in order to achieve thermal comfort and energy efficiency. Insulation reduces both unwanted heat loss on cold days/nights, and heat gain on hot days and nights, and thus decreases the requirements of heating and cooling. In the UK of course, the former is most important.
The thermal resistance of a material is referred to as its r-value. It is expressed as the thickness of the material divided by its thermal conductivity, or k-value. The u-value of a wall equates to the rate of transfer of heat through all the elements that make up the wall, and is expressed in Watts per metres squared Kelvin, or W/m²K.
In essence, insulation is all about pockets of air, which has a very low thermal conductivity (k-value), separated by material with a high resistivity (r-value). Theoretically a vacuum would be the best insulator, but since this is not practical the next best thing is to have lots of fluffy stuff – air pockets separated by thin strands of material with high r-value.
Oil-based insulation materials contain lots of little air bubbles separated by plastic and have good k-values, meaning a relatively thin board (50mm) will have a good r-value and enable good u-values for a reasonably thin wall make-up. There are more modern ‘space-age’ materials which have the best k-values, such as Aerogels, but they are prohibitively expensive to use in any thickness and so do not necessarily give good u-values overall. Oil-based materials aren’t necessarily best though – see our Materials section.
How much insulation your house should have is really a moot point – it is unlikely that you’ll be able to insulate enough for zero heat loss, due to practicalities and cost, and so the general rule of thumb is to try and have as much as you can. Building regulations now require good insulation levels for new buildings, however going beyond this is recommended if possible.
See Materials for the pros and cons of all insulation materials.