16 Jan 2009
The multifoil products need to be used with care. If you install them wrongly (i.e. without a non-ventilated air gap, preferably on both sides) they have very little effect - the same amount you might expect from any other insulant that's only a few mm thick. Some of the companies that make the stuff have been rather optimistic in their marketing claims too, so watch out for that. At least one company had a telling off from the advertising standards folk and there have been tales of them still managing to flout the rules by changing the name of their product regularly, whilst maintaining the original false claim. There are no such issues with the thick and fluffy stuff, so if you've got room for it, that's a safe bet.
20 Jan 2009
This is a really useful and informative piece. It answers a lot of the questions I have about loft insulation.
However, have you done any comparative calculations on the likely return on investment for each option?
i.e. how long does each option take before the money saved equals the money spent?
23 Jan 2009
Payback depends mainly on how bad your heat loss is to start with. If you're losing £250 worth of heat per year through your roof, that's the most you can save by insulating. But if it's losing less in the first place because it already has some insulation or just a different construction technique, you might only be losing £100/yr. In the former case adding 200mm of fluffy insulation it will save you much more money than in the latter, so the rate of return on your investment will be totally different.
A related factor is that of diminishing returns. Starting with an uninsulated loft and adding 50mm of insulation will save a lot. Adding another 50mm (to make a total of 100) will save about half as much again as the first 50mm did (but will cost just as much to buy). A third 50mm will save half as much agai and so on. At some point the expense paid to add more will not be paid back within your expected length of occupancy, or some other reasonable length of time so it doesn't make sense to add more. For most people this limit is reached at about 300mm of mineral wool if you have gas heating and perhaps 400mm if you a more expensive heating fuel like LPG or electric heating.
30 Jan 2009
Just thougt I would add to the discussion on sheep wool insulation having recently built the first dedicated factory to manufacture sheep wool insulation - www.BlackMountainInsulation.com . Sheep are not bred for their wool any more, Sheep are only bred and kept for livestock farming.
We source wool that is not required by others namely balck or grey wools, this is definitely a by product and is a category 3 waste product and hence cannot be thrown away to landfill. Methane is certainly not produced due to sheep wool insulation. In fact sheep wool insulation requires 85% less energy to produce than glass fibre, it is a "carbon sink" it locks up carbon dioxide as it grows - 6 kgs per m2 of insulation. It is a better insulator (10%) than glass fibre.
Yes it is more expensive, however Black Mountain Insulation has reduced the price of sheep wool insulation by 25% due to it's new factory.