Loft insulation at ceiling level is the cheapest worthwhile energy measure in most British houses and the one most often half done. The material costs little, the labour is straightforward, and the two things that undo it are laying it too thin and boarding over it so it is squashed flat.
How much to insulate attic space: depth, and the diminishing return
Current guidance points at a considerably deeper layer than most older houses have, and the way it is achieved is a first layer between the ceiling joists and a second laid across them at right angles, which also covers the joists themselves and removes the cold bridge they create. The return diminishes with depth: going from nothing to a moderate depth is the large saving, and going from a moderate depth to the current recommendation is worthwhile and much smaller. If you have an existing layer, measuring it is the first job, because topping up is far cheaper than starting over.
Loft insulation and boarding: how boards waste the money
Laying loft boards straight onto the joists over insulation compresses it, and compressed mineral wool insulates far less than loose wool of the same original depth. That is why a boarded loft is frequently colder than the depth suggests. The correct approach is a raised platform system that lifts the boarding above the full depth of insulation on legs, leaving it uncompressed. It costs more than boards and it is the difference between storage and storage that undoes your insulation.
What it does to the loft itself
Insulating at ceiling level makes the loft space colder, which is the point and has consequences. Water tanks and pipes up there need lagging or they will freeze. The eaves ventilation path has to stay clear, so insulation must not be stuffed into the eaves, and eaves trays keep the gap open while letting it run out to the wall plate. And a colder loft is more prone to condensation if warm moist air is getting up there through the hatch, downlighters and service penetrations, so sealing those is part of doing it properly.
Best loft insulation materials, and the flammability question
Mineral wool and glass wool rolls are the standard and are non combustible or essentially so, which is one reason they dominate; the paper or foil facing on some products is not the insulation itself. Rigid boards are used where depth is limited, such as between rafters in a room in the roof. Blown loose fill suits awkward spaces. For a loft conversion the insulation line moves to the rafters entirely, which is a different and more demanding problem than laying rolls at ceiling level.
Grants and loft insulation installers, honestly
Insulation is one of the measures government backed schemes do fund, unlike glazing, so the answer here is more positive. Eligibility normally runs through the household's benefits, the property's energy rating and sometimes local authority criteria rather than through age alone, so there is no scheme that funds loft insulation simply because someone is a pensioner. Many older households qualify for other reasons. Check the current position on GOV.UK and with your local authority, and expect a scheme to require a registered installer working to a recognised standard.
Questions people ask about loft insulation cost UK
How deep should loft insulation be?
Current guidance points at a considerably deeper layer than most older houses have, laid as one layer between the joists and a second across them. Measure what is there first: topping up is much cheaper than starting again.
Can I board over loft insulation?
Not directly. Boards laid on the joists compress the insulation and waste much of the benefit. Use a raised platform system that keeps the boarding above the full depth.
Is there free loft insulation for pensioners?
Not on age alone. Government backed schemes do fund insulation, with eligibility running through benefits, the property's energy rating and local criteria. Many older households qualify for those reasons rather than because of age.
Does loft insulation need replacing?
Mineral wool does not wear out in normal conditions, though it can be compressed, disturbed, contaminated or wet, all of which reduce it. Topping up over sound existing insulation is usually better than removing it.