When it comes to insulating your house for the coming winter, don’t ignore sheep’s wool.

If we know anything about sheep, it is that they don’t freeze to death in fields during the winter, so suppliers who recommend such materials for keeping houses warm, might be on to a good thing.

Sheep wool is now being used extensively to make rolls of loft insulation material. And experts reckon it is up to 20% more efficient, meaning that you only need a depth of 225mm of sheep’s wool insulation, as opposed to 270mm of normal (fibreglass) insulation.

Now this depth figure is important, because it is the government’s minimum recommended thickness needed to keep the heat inside the house and not heating the street outside. And this figure is not arrived at in an arbitrary fashion. It’s derived at by estimating the amount of fibreglass (depth) needed to arrive at the standard of current loft insulation of 0.16W/m2K. This might sound like a tricky mathematical formula, but it refers to watts per square metre per degree Kelvin. This is referred to as the U-value and the lower the U-value, the better the insulating effect.

The trouble is of course, and this is a fact that many DIY insulators find to their cost, is that most attic roof joists are 100mm deep, which means that the insulation is way thicker than the joists. And if you want your attic boarded over to create a usable floor, then you cannot just compress the fibreglass as it’s insulating properties will be cancelled out. So, people who want to board over are usually faced with the decision of having to add to the current joists with new pieces of timber up to the required depth.

Adding new timbers in even a comparatively small loft space can be an expensive and time consuming job, which will dramatically increase the cost of insulation.

The base cost of laying down fibreglass is around £5 per square metre. If you choose say mineral wool fibre, which is said to not irritate the skin so much as fibreglass when laying, you still need a depth of 270mm, but it will set you back nearer £8 per square metre. You can get various types of non irritant fibreglass and lesser thicknesses, all achieving the desired U-value of 0.16, but some of these will cost between £10 and £25 per square metre.

And sheep’s wool? That will cost you £20 per square and say the salesmen, this will last the lifetime of the house and will not degrade like synthetic and mineral fibres, which will eventually collapse and lose their insulation properties.

Guest Article by Neil Camp

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