Insulation is priced by the square metre of the thing being insulated, and the measures are a long way apart: the loft is the cheapest surface in the house to treat and a solid wall is among the dearest. The awkward part is that most installers publish no price at all, so a homeowner comparing measures is usually comparing one firm's guess with another firm's silence. This hub reads what is actually published and keeps it as a dated index.
What each measure is published at, from this hub's own index
The Roofing Quotes UK Insulation Measure Price Index reads published figures off installers' own pages and keeps each one as a verbatim quote with its date. Read on 26 September 2026, the median published figure across it was £47.50 per square metre, with a range of £15 to £110. By measure, the published medians were £25 per square metre for cavity wall, £25 for spray foam, £60 for an underfloor measure from below, £100 for internal solid wall and £100 for external wall insulation. Those are rates per square metre of the surface treated, not a price for a house, which is why a cavity wall job on a whole semi still lands in the hundreds rather than the thousands while external wall insulation on the same house does not.
Most installers publish nothing, which is the most useful finding in it
Of the 51 named sources that could be read in full, 6 published a usable figure and 45 published none. That is not an accident of who we happened to read: a measure whose price depends on the wall build up, the access and the grant status is genuinely hard to advertise, and a firm that advertises one is usually advertising the cheapest case. Treat any single published rate as the bottom of a range, and treat a quote that matches it exactly as a quote that has not yet seen the house.
What a home insulation survey looks at before anybody quotes
A proper survey establishes what the walls are built of and whether there is a cavity to fill, how deep the existing loft insulation is and whether it is still doing anything, where the ventilation paths run, and whether there is damp that insulating would trap rather than cure. On a grant funded job an assessment against the retrofit standards comes first and produces a plan for the whole house rather than one measure, which is the point of it: insulating one element of a leaky house moves the moisture problem somewhere else. Be clear which you are being offered, because a free survey from an installer is a sales visit with a tape measure, and that is not the same document.
Why the same measure is quoted at two very different rates
Access is the commonest reason. A loft with a small hatch, no boarding and a low pitch is slower to work in than an open one, and an underfloor measure is a different job with a crawl space than without. A cavity that has been filled once already may need extracting before anything else happens, which is its own line. External wall insulation needs scaffolding, and the render finish on top of it is a trade in its own right. And where the property is in a conservation area or is listed, the external option may not be available at all, which pushes the answer inside and changes the room.
Where a grant changes the number rather than the work
The funded schemes move who pays rather than what gets installed, and eligibility usually turns on the household's benefits, the property's energy rating or the area rather than on the measure. Two things follow. A grant funded installation runs to the retrofit standards and through a registered installer, which is a protection rather than a hoop. And a firm that tells you a grant covers everything, without asking a single question about the household, is not quoting a grant. Check the scheme yourself before signing anything.
Questions people ask about insulation costs
Which insulation measure is the best value?
The loft, almost always, and by a wide margin: it is the cheapest surface to treat and the one losing the most heat in a typical British house. Walls come next and cost several times as much per square metre. Floors are usually last unless the floor is suspended timber over a ventilated void.
Why is my quote so much higher than the published rate?
A published rate is a rate for the surface, and a quote is for a job: access, extraction of a previous fill, scaffold, making good, and the parts of the house where the measure does not simply repeat. Ask for the rate and the extras as separate lines and the difference usually explains itself.
Does insulation need building regulations approval?
Insulating a roof or a wall as part of a renovation engages the energy efficiency requirements, and the installer signs the work off or building control does. Where the work is grant funded it also runs through the retrofit standards, which is a separate framework with its own paperwork.
Is spray foam a cheap way to insulate a roof?
It reads cheap per square metre and it is the measure most likely to cost money later, because some lenders and surveyors treat sprayed roof timbers as a defect to be investigated. Read the spray foam page before treating the rate as a saving.