How much does it cost to insulate a terraced house?
The short answer
- £500 to £650 for loft insulation and £1,100 for cavity walls in a mid-terrace
- About £94 a year saved by cavity wall insulation in a 3 bed terrace on gas, a 12 year payback at full price
- £12,000 to £15,000 for solid walls, common in older terraces, which pays best with a grant
Updated 25 September 2026. Every figure on this page comes from our published model; see where our data comes from.
Insulating a terraced house costs from about £500 to top up the loft to £12,000 or more for solid walls. Cavity wall insulation costs about £1,100, the Energy Saving Trust's figure for a mid-terrace house, and homes that had it fitted used a median 12.0% less gas afterwards.
What each measure costs
Loft first, then the walls. For a 3 bed terraced house on gas, cavity wall insulation saves about £94 a year and pays back in 12 years; solid walls save more but cost far more.
| Measure | Typical cost | Saving a year | Payback |
|---|---|---|---|
| Loft insulation, bare loft to 270mm | £650 | More than £25 | Under 26 years |
| Loft insulation, top-up from 120mm | £500 | £25 | 20 years |
| Cavity wall insulation | £1,100 | £94 | 12 years |
| Solid wall insulation, internal | £12,000 | £135 | Over 50 years |
| Solid wall insulation, external | £15,000 | £135 | Over 50 years |
| Suspended timber floor | £1,400 to £2,500 | About £40 (Trust estimate) | 35 to 62 years |
The data behind this table
Costs: Energy Saving Trust, typical professional installation before any grant: loft and cavity figures for a mid-terrace house (updated 8 May 2026), solid wall figures for a typical home (18 June 2026), suspended floors £1,400 to £2,500 depending on the house (19 May 2026). An end-terrace, which the Trust does not price, is closer to a semi-detached house: see our semi page. Savings: the median fall in gas use measured in real homes after each measure (DESNZ NEED Impact of Measures 2026, Table 1: loft 3.2%, cavity wall 12.0%, solid wall 17.3%), applied to a 3 bed terraced house with average insulation at the October 2026 cap price of 7.97p per kWh. The loft figure is the median across all loft jobs, most of them top-ups, so insulating a bare loft saves more. Floor savings are the Trust's own estimates. Payback is cost divided by the yearly saving, at full price. Homes heated by oil, LPG or electricity save more in pounds.
Cavity or solid walls?
Check before you price anything. Homes built from the 1930s usually have cavity walls, which are far cheaper to insulate; brickwork showing the short ends of some bricks means solid walls. Your EPC records the wall type.
Solid wall insulation costs about £12,000 fitted inside or £15,000 outside, and saves about £135 a year here, so at full price it only pays with a grant. Read is cavity wall insulation worth it and solid wall insulation cost.
Loft and cavity together
About £1,750 for both. Homes that had loft and cavity wall insulation fitted together used a median 8.4% less gas, about £65 a year here; that is a different group of homes from the single-measure figures, so the two cannot be compared directly.
In our EPC model the loft adds about 7 points and cavity walls about 8, often enough to lift a home a band. Insulating first also shrinks the heat pump a 3 bed terraced house needs, from 8 kW at average insulation to 7 kW well insulated. Plan the whole job with the retrofit plan, or check your own home in the insulation calculator.
Savings by size of terraced house
Bigger homes save more. These are the measured savings a year for homes heated by gas, with average insulation to start with.
| Home, heated by gas | Loft | Cavity walls | Solid walls |
|---|---|---|---|
| 2 bed terraced house | £18 | £67 | £96 |
| 3 bed terraced house | £25 | £94 | £135 |
Compare other types of home: semi-detached house, detached house, bungalow or flat, or see them side by side in insulation cost by house type.
Grants that can pay for it
ECO4 until 31 December 2026, then council grants. ECO4 funds insulation for households on qualifying benefits, in homes rated D to G if owned or E to G if privately rented, and the work must be finished by then.
In England a Warm Homes: Local Grant through your council can help households on lower incomes, and insulation carries 0% VAT until 31 March 2027. Landlords can check the 2030 band C rules with the landlord EPC calculator.
Frequently asked questions
How much does it cost to insulate a terraced house?
From about £500 to top up the loft to £12,000 for internal solid wall insulation, at Energy Saving Trust prices before any grant. Cavity wall insulation costs about £1,100 for a mid-terrace house.
Is cavity wall insulation worth it for a terraced house?
Homes that had it fitted used a median 12.0% less gas, about £94 a year for a 3 bed terraced house on gas, so at about £1,100 it takes 12 years to pay back at full price. It can be free through ECO4 for households on qualifying benefits, and it adds about 8 EPC points in our model.
Can I get insulation for my terraced house free?
Possibly. ECO4 funds insulation for households on qualifying benefits until 31 December 2026, in homes rated D to G if owned or E to G if privately rented, and in England a Warm Homes: Local Grant through the council can help households on lower incomes. Insulation carries 0% VAT until 31 March 2027.
Data sources
- Energy Saving Trust, cavity wall, loft, solid wall and floor insulation advice, May and June 2026.
- DESNZ, NEED Impact of Measures 2026, 11 June 2026.
- Ofgem, energy price cap, October to December 2026.