Loft Insulation Cost Calculator

How this calculator works

This calculator works in ranges rather than single figures, because real quotes, yields and tariffs genuinely vary that much. It starts from typical UK price, output and savings ranges drawn from published 2026 industry guides and official scheme documentation, then scales them by the quantities you enter and adjusts them for each choice you make below. The result is a low-to-high band that a realistic outcome is likely to fall within, not a promise of the figure you will achieve.

Professional loft insulation costs roughly to per square metre installed in 2026, putting a typical terraced house around , a semi to and a detached house up to , while confident DIYers can do the job in mineral wool rolls for or so in materials. An uninsulated roof loses around a quarter of a home’s heat, and upgrading saves in the region of to a year for a typical semi at 2026 prices, one of the quickest paybacks anywhere in home energy.

Area to insulate (square metres)

Measure the loft floor area, which matches the footprint of the rooms below it. A terraced house is typically 30 to 40 square metres, a semi 40 to 55 and a detached 60 to 100. If you can only estimate, the floor area of your top storey is the same number.

Job type

Building Regulations guidance targets around 270 mm of mineral wool at joist level, laid in two layers with the top layer crossing the joists. Topping up an existing 100 mm layer needs less material and time, while going beyond 270 mm adds modest material cost for diminishing but real returns. If your loft has 100 mm or less, an upgrade is one of the best-value jobs in home improvement.

Loft condition

A clear loft with a decent hatch is a half-day job. Stored belongings that need moving, existing boarding that must be lifted or raised, downlighters needing covers, and pipes or tanks needing separate lagging all add time. If you want to keep storage, raised loft legs and new boarding over the full insulation depth typically add to for a storage area rather than the whole loft.

Where you live

Installation labour is not priced uniformly across the UK, with published guides putting London and South East insulation quotes roughly 15 to 25 percent above the national average. Materials are broadly national in price, so the difference sits mostly in labour, access and parking.

What else affects the figures

Mineral wool quilt remains the default for good reason, cheap, non-combustible and proven, while rigid PIR boards at to per square metre suit lofts where headroom or storage matters and blown fibre suits awkward or low spaces. Ventilation is the detail that separates good jobs from bad: insulation must not block eaves airflow, and bathroom extract ducts should discharge outside rather than into the newly cosy loft, or condensation follows. The loft hatch deserves insulating and draught-stripping too, and water tanks and pipes above the insulation need lagging since the loft itself will now be colder. Eligible households can have loft insulation fully funded under ECO4 or the Great British Insulation Scheme.

Certification, planning and grid connection

Adding insulation to an existing element generally needs no planning permission, but Building Regulations Approved Document L applies whenever a thermal element is renovated or replaced, setting U-value targets the work should meet, and some measures are notifiable through building control or a competent person scheme, which reputable installers handle as standard. Ventilation is the companion rule: a better-insulated, more airtight home needs deliberate air movement, so eaves gaps, airbricks, trickle vents and extractor fans must be preserved or improved alongside the insulation. Grant support is substantial, with ECO4 running to 31 December 2026 and the Great British Insulation Scheme funding measures for eligible households, both requiring TrustMark-registered or suitably certified installers, and domestic insulation carries 0 percent VAT until 31 March 2027.