Everyone should have their loft insulated as this is a relatively easy way to save money. Although you may have the initial outlay this is usually recouped within a couple of years through reduced heating bills and a properly insulated loft can save you up to 20%. Lawsons are the place to come to for all your insulation needs!
The product is generally supplied in roll form, although loose fill is available, and is made from mineral wool (glass or rock wool) which being a soft, pliable material, makes it easy to unroll between joists. This acts as a blanket helping to prevent heat-loss into the loft space which eventually would escape through the roof.
The recommended thickness, dependant on material, is 270-250mm and this can be made up of more than one layer, especially if you already have a thinner layer of say 100-75mm. There is no need to remove the old layer as the insulant value will still be retained no matter how old it is.
To insulate your loft is a relatively easy job but remember to wear appropriate PPE such as gloves, face mask and even goggles, if you feel this is better done by an expert check the EST (Energy Saving Trust) Register for your local installer; there may even be a grant available towards the cost.