Does an extension pay for itself? What 112,630 extended homes show
Sale prices of houses in England and Wales before and after they were extended, matched to their Energy Performance Certificates, set against what an extension costs to build, and how energy upgrades change the picture.
Sale-price uplift from extending
+17.8%
£1,907 per m² added, England and Wales
Build cost recovered, London
118%
Adds £3,325 per m² against £2,820 to build
Build cost recovered, North East
51%
Adds £1,023 per m² against £2,000 to build
Extended and energy rating improved
+24.3%
Against +8.2% where the rating stayed the same
Key findings
- Extending adds a similar share of the price across the country, so the money follows local house prices: £3,325 per m² in London, £1,023 in the North East.
- Against the all-in build cost, the typical extension comes out ahead only in London. Everywhere else it adds less to the sale price than it cost, down to 51% in the North East.
- Detached houses gain the most and terraces the least. Terraces in the Midlands and the North recover the smallest share of their cost.
- Energy performance goes with value. Extensions where the EPC energy score also rose gained +24.3%, against +8.2% where it did not. Improving the rating without extending was linked to +5.4%.
- Moving to get the same space has its own costs that never come back (agent, Stamp Duty or Land Transaction Tax, conveyancing, removals), which is the fairer comparison for most owners.
What an extension adds per m², against what it costs to build
Median sale-price uplift per m² added, second sales 2016 to 2026. Build cost: buildwiz.uk all-in estimate per m², ex kitchen, by region.
Right-hand column: share of the build cost added to the sale price.
Show data
| Region | Value added per m² | Build cost per m² | Recovered |
|---|---|---|---|
| London | £3,325 | £2,820 | 118% |
| South East | £2,414 | £2,470 | 98% |
| South West | £2,027 | £2,470 | 82% |
| East of England | £2,015 | £2,470 | 82% |
| West Midlands | £1,607 | £2,350 | 68% |
| East Midlands | £1,557 | £2,350 | 66% |
| Yorkshire and The Humber | £1,356 | £2,000 | 68% |
| North West | £1,352 | £2,000 | 68% |
| Wales | £1,181 | £2,120 | 56% |
| North East | £1,023 | £2,000 | 51% |
| Region | Houses | Value added per m² | Middle half | Build cost per m² | Recovered |
|---|---|---|---|---|---|
| London | 12,362 | £3,325 | £1,146 to £5,846 | £2,820 | 118% |
| South East | 23,160 | £2,414 | £701 to £4,141 | £2,470 | 98% |
| South West | 14,968 | £2,027 | £465 to £3,705 | £2,470 | 82% |
| East of England | 13,058 | £2,015 | £358 to £3,601 | £2,470 | 82% |
| West Midlands | 9,201 | £1,607 | £170 to £3,047 | £2,350 | 68% |
| East Midlands | 8,819 | £1,557 | £248 to £2,877 | £2,350 | 66% |
| Yorkshire and The Humber | 11,497 | £1,356 | £97 to £2,787 | £2,000 | 68% |
| North West | 11,831 | £1,352 | £22 to £2,883 | £2,000 | 68% |
| Wales | 4,111 | £1,181 | £31 to £2,725 | £2,120 | 56% |
| North East | 3,623 | £1,023 | £29 to £2,450 | £2,000 | 51% |
By house type
Detached houses are extended more, in pricier streets, and gain the most per m². A terrace on a street of similar terraces can only rise so far above its neighbours.
| House type | Houses | Typical m² added | Sale-price uplift | Value added per m² |
|---|---|---|---|---|
| Detached | 43,777 | 38 m² | +22.5% | £2,250 |
| Semi-detached | 37,708 | 28 m² | +18% | £1,825 |
| Terraced | 31,145 | 26 m² | +12.1% | £1,412 |
| All houses | 112,630 | 30 m² | +17.8% | £1,907 |
Share of the build cost recovered, region by house type
| Region | Detached | Semi-detached | Terraced |
|---|---|---|---|
| London | 113% | 107% | 125% |
| South East | 115% | 93% | 63% |
| South West | 97% | 75% | 58% |
| East of England | 92% | 81% | 55% |
| West Midlands | 88% | 64% | 32% |
| East Midlands | 80% | 59% | 23% |
| Yorkshire and The Humber | 96% | 74% | 29% |
| North West | 98% | 73% | 26% |
| Wales | 74% | 53% | 34% |
| North East | 76% | 55% | 27% |
Energy performance and sale prices
Each certificate records an energy efficiency score as well as a floor area, so the same comparison shows how energy upgrades and sale prices move together. "Energy score up" means the EPC score rose by 5 points or more between the two sales.
| Region | Extended, energy score up | Extended, score unchanged | Energy score up, not extended | Homes sold rated A to C |
|---|---|---|---|---|
| London | +20.5% | +10.7% | +2.4% | 48% |
| South East | +25.0% | +8.8% | +4.2% | 53% |
| South West | +26.1% | +8.7% | +5.8% | 51% |
| East of England | +24.7% | +8.3% | +4.2% | 53% |
| West Midlands | +24.0% | +7.6% | +5.8% | 47% |
| East Midlands | +26.2% | +7.3% | +6.4% | 52% |
| Yorkshire and The Humber | +25.0% | +8.7% | +6.5% | 46% |
| North West | +24.8% | +7.0% | +5.9% | 48% |
| Wales | +23.5% | +6.5% | +7.5% | 43% |
| North East | +25.1% | +7.3% | +8.0% | 54% |
| England and Wales | +24.3% | +8.2% | +5.4% |
Median sale-price uplift against similar houses whose floor area and energy score barely changed. Last column: share of homes sold in the last three years whose certificate at sale was rated A to C.
- Read these as associations, not as the value of insulation alone. A house whose rating jumps has usually had new windows, heating or a wider refurbishment at the same time.
- Owners who are extending anyway are opening walls and roofs, which is the cheapest moment to insulate. The gap between the first two columns is what buyers paid for an extended home that was also upgraded.
Other patterns
- Loft conversions: houses whose certificate recorded a new room in the roof gained about 23%, close to a ground-floor extension per m².
- The market matters: extended houses with a second sale between 2016 and 2021 gained 19-20%; those sold from 2023 gained 14-16%, falling as house prices flattened.
- Neighbourhood: value added per m² rises steadily from the most to the least deprived areas.
- Ground conditions: clay soil, radon and flood zones barely change the value added. They change the build cost instead, through deeper foundations, membranes and drainage.
Method
We matched HM Land Registry Price Paid sales to MHCLG Energy Performance Certificates, using Ordnance Survey's unique property reference numbers, so each sale has the floor area and energy score on the certificate in force at the time. Checked against HM Land Registry's own sale-to-property lookup, our matching agrees on 99.8% of the sales both cover.
We took standard sales of houses (detached, semi-detached and terraced) that sold twice at least two years apart. A house counts as extended when a certificate issued between the sales records at least 15 m² and a tenth more floor area. The comparison group is houses whose floor area changed by 3 m² or less and whose energy score moved by 4 points or less.
For each extended house we take its price growth between the two sales, less the median growth of comparison houses in the same council, of the same type and sold in the same pair of years. That difference, in pounds at the second sale and divided by the floor area added, is the value added per m². Every figure is a median for a group of at least 100 houses. The comparison group itself centres on zero, as it should.
Build cost is the all-in estimate per m² used by our extension cost calculator: builder, specialist trades, glazing, floors and professional fees, before the kitchen, with a regional adjustment. It agrees with the cost per m² of the documented extension behind this site.
Limitations
- These are medians from past sales, not a valuation of any one home. The middle-half ranges show how wide the spread is.
- Only houses that sold twice are counted. Owners who extended and stayed are not.
- The uplift includes refurbishment done at the same time. Houses that got a new certificate but whose recorded floor area fell gained about 3%, which sets the size of that effect.
- EPC floor areas are assessor estimates, so small changes are noise. That is why an extension must add at least 15 m².
- Build costs are a model with regional adjustments, not quotes. Your own quote will differ.
Cite and reuse
The tables, chart and CSV are free to reuse under the Open Government Licence v3.0. Please cite:
buildwiz.uk, Extension value and energy performance, England and Wales (analysis of HM Land Registry Price Paid and MHCLG EPC data, 2026-10). https://buildwiz.uk/research/extension-value
Download the data (CSV): every region and house type, with the energy split. Only aggregates are published, never addresses or individual sales. Journalists with questions can email cmo@buildwiz.uk or contact us.
Questions
How much value does an extension add to a house?
Across England and Wales, houses extended between two sales gained a median +17.8% over similar unextended houses in the same council, of the same type and sold in the same years. That is £1,907 per m² of floor area added, from 112,630 extended houses with a second sale from 2016.
Does an extension pay for itself?
Only in some places. Set against the all-in build cost per m² (ex kitchen), the typical extension recovered 118% of its cost in London and 51% in the North East. London is the only region where the median comes out ahead. Detached houses do best and terraces worst.
Does improving a home's energy rating add value?
Houses whose EPC energy efficiency score rose by 5 points or more, with no extension, sold for +5.4% more than similar unchanged houses. Extended houses whose score also rose gained +24.3%, against +8.2% where the score stayed put. These are associations: an upgraded home usually has other work done too.
Can I use this data?
Yes. The tables, chart and CSV are free to reuse under the Open Government Licence v3.0, the same terms as the source data. Credit buildwiz.uk and the sources below, and please link to this page.
Will your extension pay for itself?
Put in your region, house type, size and quote, and compare extending with the cost of moving.
Sources
Contains HM Land Registry data © Crown copyright and database right 2026, licensed under the Open Government Licence v3.0. Energy Performance Certificate data from MHCLG, Open Government Licence v3.0. Contains OS data © Crown copyright and database right 2026.
Data generated 2026-10-06. Full method: property prices and energy performance.
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