In 40 seconds
Insulating a loft with mineral wool to the recommended 270mm depth typically costs roughly £300–£1,800 depending on the property — commonly around £300–£700 for a small terrace and up to about £900–£1,800 for a detached house, with a top-up over existing insulation at the lower end. The Energy Saving Trust puts annual savings at roughly £135–£590, so payback is often two to four years and the insulation can last around 40 years. Many households qualify for help through schemes such as the Warm Homes: Local Grant, so it is worth checking funding before paying. One firm caution: avoid spray foam in the loft, which can block a mortgage and conceal the roof timbers. The honest answer is always a range, because it depends on your loft size, access and existing insulation.
Most loft-insulation guidance is published by firms selling the work or chasing grant leads, so the numbers tend to be optimistic and the catches glossed over. The pages below give honest cost ranges, explain the grants worth checking, set out how thick it should be and whether it pays back, and flag the spray-foam trap — before you take a single quote.