The most common type of loft insulation is mineral wool in a roll, rock wool or glass wool. This is inert, inorganic, non-toxic, rot-proof and fire resistant, and should be free of CFCs and HCFCs. Manufactured to BS3533:1981, it has zero ODP (ozone depleting potential) and zero GWP (global warming potential). Another alternative is loose mineral wool, which is blown into the loft and is useful when access to roll out a loft insulation quilt is difficult. However this is a specialist rather than a DIY job. You can also buy mineral fibre encapsulated in a space blanket, which avoids irritation to the skin when laying.
Because of the irritant effects of mineral wool, and the relatively large amount of energy needed to produce it (embodied energy), some people may prefer to use natural “eco-friendly” products. They can be used on top of your existing mineral wool insulation. Options are listed below. More details and suppliers here.
Natural sheep's wool insulation
Natural woollen insulation is made using wool from British sheep and takes very little energy to manufacture. It is naturally breathable, non-irritant, clean and easy to use. Moreover, wool is inherently fire retardant, and produces no toxic gases if it burns. Products include Thermafleece and Black Mountain, both available in rolls of varying thickness. In some cases the wool is treated with inorganic salts to make it unpalatable to rodents.
Natural hemp insulation
There are several products that use hemp fibres from UK-grown hemp plants. Hemp insulation is breatheable and a good insulator, and its manufacture uses relatively small amounts of energy. And of course the hemp plants absorb carbon dioxide during growth. Bagged Loose Hemp is available from Black Mountain. This is useful for insulating gaps in awkward areas, such as around window and door frames.
Hemp fibres are also made into semi-rigid slabs, or batts, by adding a polyester binder. For example, Isonat Plus Insulation contains 30% hemp, 55% wood fibre, and 15% polyester. Hemp is treated with a fire retardant to ensure it complies with safety standards.
Dry cellulose insulation
Cellulose fibres derived from recycled newspapers are the basis for several insulation products. These exploit a sustainable resource and require much less energy to manufacture compared with mineral wool products. They are blown into loft spaces as loose fibres, which have been treated with mineral salts to act as a fire retardant and to inhibit growth of fungi and repel vermin. Some can also be bought in bags for DIY installation.
Now well established in the market are the Warmcel range of products, manufactured in South Wales. Warmcel 100 is available in 8 kg bags, each of which when distributed at a depth of 100mm covers about 2 square metres. It is easy to handle and requires no special equipment or clothing. Other Warmcel products can be damp-sprayed onto vertical surfaces, such as wall panels, but this needs a specialist contractor.
Not exactly natural, but involving recycling, this is made from 85% recycled plastic bottles. The remaining 15% is polyester to bind the fibres. Unlike the mineral wool products, this contains no loose fibres, so is claimed to be 'non-itch'. It is suitable for lofts, timber frame walls and roofs.
Using your loft for storage can be a problem if it is fully insulated. One solution is to install rigid polystyrene insulation space boards over part of the area to provide an insulated storage deck.