Loft, cavity wall, solid wall and floor, each with two measurements side by side and what it saves a year. Sources opened by me on 20 September 2026; no installer behind this page and no lead selling.
How much does insulation cost in the UK?
On a semi-detached house in Great Britain the Energy Saving Trust puts loft insulation at £750, cavity wall insulation at £2,200, a suspended timber floor at £1,400 to £2,500, and solid wall insulation at around £12,000 from the inside or £15,000 from the outside. Checkatrade, a price guide with its own estimators, lands at £825 for the loft and £2,700 for the cavity wall, and anywhere from £8,000 to £20,000 for a solid wall. Installed insulation carries 0% VAT until 31 March 2027. On the Trust's July 2026 energy prices the loft saves about £190 a year, the cavity wall £200, the solid wall £280 and the floor £55.
A semi-detached house, measure by measure
Measure
Energy Saving Trust
Checkatrade
Saves per year
Loft, from nothing to 270mm
£750
£825
£190
Loft top-up, from 120mm to 270mm
£600
not priced separately
£17
Cavity wall
£2,200
£2,700
£200
Solid wall, insulated from inside
£12,000
£8,000 to £10,000
£280
Solid wall, insulated from outside
£15,000
£10,000 to £20,000
£280
Suspended timber floor
£1,400 to £2,500
£1,500 to £3,000
£55
Professional installation, unsubsidised, Great Britain. Savings: Energy Saving Trust, gas-heated home, fuel prices as of July 2026. Checkatrade prices exclude VAT where it says so; installed insulation is zero-rated until 31 March 2027.
The semi-detached house is the one type both sources price for every measure, which is why it carries this table. The two columns measure different things: the Trust publishes a typical installation cost, Checkatrade an average collated by its own estimators. Expect your quotes to land somewhere between them.
By house type
House
Loft, 0 to 270mm
saves a year
Cavity wall
saves a year
Solid wall saves
Detached house
£1,100
£360
£3,900
£380
£500
Semi-detached house
£750
£190
£2,200
£200
£280
Mid-terrace house
£650
£140
£1,100
£110
£150
Detached bungalow
£1,200
£350
£1,700
£160
£220
Source: Energy Saving Trust, typical installation cost and energy bill savings per year, fuel prices as of July 2026.
A mid-floor flat has no loft of its own. Its cavity wall costs £950 and saves £110 a year; solid wall insulation saves it £140 a year. The Trust gives no cost per house type for solid walls or floors, only the semi-detached figures above, so I do not invent the missing cells.
Where the guides disagree
One publisher, two prices for the same wallCheckatrade prices external wall insulation on a semi-detached house at £10,000 to £12,500 in its retrofit guide and at £14,000 to £20,000 in its external wall guide, both dated summer 2026. The table above shows the full span. For floors its dedicated guide says £95 to £115 per square metre and approximately £6,000 for the average home, while its retrofit guide says £1,500 to £3,000 for a semi-detached house. Treat any single number for a solid wall or a floor as a starting point for quotes, not as a budget.
For cavity walls the three sources sit close together: £2,200 (Energy Saving Trust), £2,700 (Checkatrade) and £2,000 to £3,000 (MyJobQuote). Once quotes arrive, the quote check reads them line by line, and why quotes differ explains the gaps you will see.
Grants and VAT: what is still open
The Great British Insulation Scheme closed on 31 March 2026 (Ofgem). GOV.UK says the eligibility checker has closed and tells you to check with your supplier.
ECO4, the Energy Company Obligation, runs until 31 December 2026 (Ofgem). It is for people on certain benefits or in social housing. If you own your house it must have an energy efficiency rating of D, E, F or G; if you rent privately, E, F or G (GOV.UK).
The Warm Homes: Local Grant is only available in England, through your council. Your home needs an EPC of D, E, F or G and your household income must usually be £36,000 a year or less (GOV.UK). The council organises and pays for the work it agrees with you.
0% VAT applies to the installation of insulation until 31 March 2027; from the day after, it reverts to 5% (VAT Notice 708/6).
Amounts, deadlines and the Boiler Upgrade Scheme are on the grants page. One warning that belongs here: GOV.UK says there are quality issues with some solid wall insulation fitted through the Energy Company Obligation, and the Energy Saving Trust writes that 98% of homes fitted with external wall insulation under ECO4 and the Great British Insulation Scheme have problems that need fixing. If that is your house, the GOV.UK page in the sources below tells you what to do.
Permission, doing it yourself, and how long it lasts
Planning permission is not normally required for fitting insulation where the outside does not change (Planning Portal). Listed building or conservation area: consult your local planning authority first. The planning permission check covers the rest of your project.
A loft you can do yourself if it is easy to access, free of damp problems and not a flat roof. The recommended depth for mineral wool is 270mm.
A cavity wall is not a do-it-yourself job. A registered installer usually needs about two hours on an average home, and the work should carry a 25 year guarantee.
Correctly installed loft insulation lasts around 40 years. If the loft is damp, fix what causes the damp before adding insulation.
Insulating as part of a bigger job? The cost calculator prices the renovation around it, and the heat pump check shows what better insulation does for the heating you can choose.
Frequently asked questions
How much does insulation cost for an attic?
Going from no insulation to 270mm costs £650 on a mid-terrace house, £750 on a semi-detached house and £1,100 on a detached house, professionally fitted (Energy Saving Trust). Checkatrade's estimators put the semi-detached house at £825. Topping up from 120mm to 270mm costs about £600 and saves only £17 a year, so the big win is the loft that has nothing in it yet.
How much is insulation for walls?
It depends on which wall you have. A cavity wall is filled from outside for £2,200 on a semi-detached house (Energy Saving Trust), £2,700 according to Checkatrade and £2,000 to £3,000 according to MyJobQuote. A solid wall has no gap to fill, so it gets a new layer inside or outside: around £12,000 inside and £15,000 outside on a three-bedroom semi-detached house (Energy Saving Trust).
Do I need planning permission for external wall insulation?
The Planning Portal says planning permission is not normally required for fitting insulation where there is no change in external appearance, and that you should consult your local planning authority if the building is listed or in a conservation area. External wall insulation does change how a house looks, so I would ask the local planning authority before ordering it. Loft, cavity and floor insulation leave the outside as it was.
Can I install insulation myself?
A loft: yes, says the Energy Saving Trust, but only if it is easy to access, free of damp problems and not a flat roof. A suspended timber floor may be possible if you are confident in your skills. A cavity wall is not a job you can do yourself: it needs a registered installer. One thing to know before you buy the rolls yourself: the 0% VAT covers insulation that a business installs, and VAT Notice 708/6 says the sale of energy-saving materials by a retailer is always standard-rated.
How long does insulation last?
Loft insulation that is installed correctly has a lifespan of around 40 years, according to the Energy Saving Trust. Cavity wall work should come with a 25 year guarantee from the Cavity Insulation Guarantee Agency or an independent insurance-backed guarantee.
How long does insulation take to install?
For cavity walls on an average home with easy access the Energy Saving Trust says about two hours; MyJobQuote says most jobs take 2 to 6 hours. For the other measures I found no duration in a source I trust, so I leave it out.
Sources, each one opened by me
Energy Saving Trust, Roof and loft insulation (independent advice; dated 8 May 2026; opened 20 September 2026). Professional installation, unsubsidised, in a gas-heated home. "Figures are based on fuel prices as of July 2026." The source does not mention VAT.
Energy Saving Trust, Cavity wall insulation (independent advice; dated 8 May 2026; opened 20 September 2026). Professional installation, unsubsidised, in a gas-heated home. "Figures are based on fuel prices as of July 2026." The source does not mention VAT.
Energy Saving Trust, Solid wall insulation (independent advice; dated 18 June 2026; opened 20 September 2026). Paying a company to insulate the whole house in one go. "Costs may vary significantly depending on level of work required." Fuel prices as of July 2026. The source does not mention VAT.
Energy Saving Trust, Floor insulation (independent advice; dated 19 May 2026; opened 20 September 2026). Professional installation in a gas-heated home, fuel prices as of July 2026. The chart caption on the same page says "around £2200" for a typical suspended floor. The source does not mention VAT.
Checkatrade, How much does loft insulation cost in 2026? (price guide; dated July 2026; opened 20 September 2026). Materials and labour, before VAT ("+VAT"). Installed insulation is zero-rated until 31 March 2027, so nothing is added today. Checkatrade sells leads to tradespeople for a monthly cost, in its own words on join.checkatrade.com (opened 20 September 2026). It serves here as a measurement, not as a recommendation. The guide calls its own figures "ballpark averages", verified by estimators who are CIOB and RICS members.
Checkatrade, How much does cavity wall insulation cost in 2026? (price guide; dated July 2026; opened 20 September 2026). An installed job; the page does not say whether VAT is included. Checkatrade sells leads to tradespeople for a monthly cost, in its own words on join.checkatrade.com (opened 20 September 2026). It serves here as a measurement, not as a recommendation.
Checkatrade, How much does retrofit insulation cost in 2026? (price guide; dated July 2026; opened 20 September 2026). An installed job on a semi-detached house; the page does not say whether VAT is included. Checkatrade sells leads to tradespeople for a monthly cost, in its own words on join.checkatrade.com (opened 20 September 2026). It serves here as a measurement, not as a recommendation. Same publisher as the other Checkatrade guides, so together they count as one measurement.
Checkatrade, External wall insulation cost: 2026 UK guide (price guide; dated July 2026; opened 20 September 2026). Insulation board, fixings, render or cladding, and labour, before VAT ("Cost+VAT"). Checkatrade sells leads to tradespeople for a monthly cost, in its own words on join.checkatrade.com (opened 20 September 2026). It serves here as a measurement, not as a recommendation. It contradicts the retrofit guide of the same publisher, which puts external wall insulation on a semi-detached house at £10,000-£12,500.
Checkatrade, Floor insulation: Cost breakdown 2026 (price guide; dated May 2026; opened 20 September 2026). Insulation and materials, before VAT ("Cost + VAT"); "replacement boards would be an additional cost". Checkatrade sells leads to tradespeople for a monthly cost, in its own words on join.checkatrade.com (opened 20 September 2026). It serves here as a measurement, not as a recommendation. Its £6,000 average sits far above the £1,500-£3,000 the retrofit guide of the same publisher gives for a semi-detached house.
MyJobQuote, Cavity Wall Insulation Cost (price guide; dated 27 May 2026; opened 20 September 2026). A straightforward installation with mineral wool or entry-level EPS beads, no old insulation to remove; the page does not say whether VAT is included. MyJobQuote sells job leads to tradespeople, in its own words on myjobquote.co.uk/tradespeople (opened 20 September 2026). It serves here as a measurement, not as a recommendation.
GOV.UK, Energy-saving materials and heating equipment (VAT Notice 708/6) (official; dated 31 January 2024; opened 20 September 2026). Applies to materials installed in residential accommodation, insulation included (section 2.10 of the notice). Rolls you buy from a retailer and fit yourself are standard-rated.