How much does loft insulation cost in the UK?

The headline: £500–£1,500

Loft insulation is the bargain of the energy-efficiency world. Topping up thin existing insulation to the recommended 270mm typically costs £500–£900 for a 3-bed home (estimate, checked October 2026). Insulating a completely bare loft from scratch runs £900–£1,500 (estimate). Either way it's a fraction of what solar panels or a heat pump costs — and per pound spent, it saves more.

The 270mm rule, explained

The UK recommendation is 270mm of mineral wool: usually 100mm laid between the joists with 170mm cross-laid over the top. If your loft has the sad 25–50mm quilt many 1980s–90s homes were left with, you're getting a fraction of the benefit — topping up is the single best-value job on this page.

Go up into the loft with a tape measure. If you can see the tops of the joists poking through the insulation, you need more. This two-minute check beats any online calculator.

What does it save?

An uninsulated loft leaks about a quarter of a home's heat straight through the roof. Taking a 3-bed semi from nothing to 270mm typically saves £200–£300 a year on heating bills (estimate) — payback in roughly 3–5 years. Topping up from 100mm to 270mm saves less, more like £50–£100 a year (estimate), but at £500–£900 installed it still pays back comfortably.

It also makes everything else work better: insulation is what lets a heat pump run efficiently and what keeps solar-heated homes warm after sunset. Do the fabric first, then the fancy kit.

DIY or professional?

Laying mineral wool rolls is genuinely DIY-able — it's one of the few energy jobs that is. But the pitfalls are real: don't block the eaves ventilation (lofts need airflow to avoid condensation), don't squash the insulation (compressed wool insulates far less — use loft legs if you need storage boards above it), keep it clear of recessed downlights (fire risk — use proper covers), and keep it away from flues and extractor terminations.

A professional job costs more but includes the survey, proper ventilation gaps, pipe and tank insulation, and a guarantee. If your loft is a maze of boards, wiring and water tanks, paying someone is money well spent. Either way, wear a mask and gloves — the fibres are miserable.

Grants can cover it

Check grant eligibility before paying: ECO4 funds loft insulation for eligible low-income households until 31 December 2026, and the Great British Insulation Scheme covers it too — including a "general group" for homes in lower council-tax bands regardless of benefits. Run our insulation savings calculator to see your numbers first.

Boarding, lighting and ventilation: the details that matter

Most loft jobs aren't just "roll out the wool". The details that separate a good job from a future headache:

Storage. If you want to keep using the loft for storage, the insulation must not be squashed under boards — compressed insulation barely insulates. The fix is raised loft legs (plastic stilts that lift boards above the 270mm layer), adding roughly £200–£400 to the job (estimate). Leave a proper walkway to the hatch while you're at it.

Lighting. Recessed downlights in the ceiling below get hot: insulation must be kept clear of them with proper fire-rated covers, not just tucked around. Your installer or electrician should handle this — it's not a corner to cut.

Ventilation. Lofts need airflow at the eaves to carry moisture away. Insulation pushed tight into the eaves blocks it and causes condensation on the roof timbers. A good installer fits eaves vent trays or baffles to keep the air path open.

The hatch and services. Insulate the loft hatch itself (an uninsulated hatch is a heat-sized hole in your new blanket), lag any exposed pipes and the cold water tank, and make sure extractor fans still vent properly to the outside.

Flat roofs and rooms-in-roof

None of the above applies cleanly to flat roofs or loft conversions: those need rigid insulation boards fitted between or above rafters — a different, pricier job (often £1,500–£3,000+, estimate) that usually means scaffolding and sometimes re-roofing. If your "loft" is a converted bedroom, get a specialist survey rather than a standard loft quote.

FAQs

How much does loft insulation cost in the UK?

£500–£900 to top up to 270mm, or £900–£1,500 from scratch for a 3-bed home (estimates, October 2026).

What is the 270mm rule?

The recommended minimum depth for mineral wool loft insulation: 100mm between joists plus 170mm across them.

How much does it save on bills?

From nothing to 270mm: roughly £200–£300 a year for a 3-bed semi (estimate). Top-ups save less but still pay back.

Can I install it myself?

Yes, but don't block eaves ventilation, don't compress it, and keep it clear of downlights and flues.

Is there a grant for loft insulation?

ECO4 (to 31 December 2026) and the Great British Insulation Scheme can both fund it for eligible households.