Cost My Extension

Cost index

London extension and loft cost index, October 2026

Typical all-in totals for a good-quality finish on a typical house: one row for each of London's 32 boroughs and one column for each kind of job. Every figure comes from the same cost engine that prices our report, includes VAT, and is shown as a range with the build cost per m² beneath it. Pick a figure to see that borough's full breakdown.

Rates checked 20 October 2026. Statutory fees from 1 April 2026. All figures include VAT.

Download the index as a CSV fileHow the numbers are worked out
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Totals and build cost per m² by borough

32 boroughs

Each cell is the total to have available for the main job in that family, on a typical two-storey house, before extras such as a new kitchen, bathroom or bifold doors. Build cost per m² is the build cost alone (before fees and contingency) divided by the area priced.

BoroughHouse extensionSide-return extensionLoft conversion
Barking and Dagenham£57,000 to £107,000£2,600 to £4,350 build cost per m²£42,000 to £82,000£3,050 to £5,200 build cost per m²£58,000 to £109,000£1,650 to £2,800 build cost per m²
Barnet£61,000 to £114,000£2,800 to £4,700 build cost per m²£45,000 to £87,000£3,300 to £5,600 build cost per m²£63,000 to £116,000£1,800 to £3,000 build cost per m²
Bexley£57,000 to £107,000£2,600 to £4,350 build cost per m²£42,000 to £82,000£3,050 to £5,200 build cost per m²£58,000 to £109,000£1,650 to £2,800 build cost per m²
Brent£61,000 to £114,000£2,800 to £4,700 build cost per m²£45,000 to £87,000£3,300 to £5,600 build cost per m²£63,000 to £116,000£1,800 to £3,000 build cost per m²
Bromley£60,000 to £111,000£2,750 to £4,550 build cost per m²£44,000 to £85,000£3,200 to £5,450 build cost per m²£61,000 to £113,000£1,750 to £2,900 build cost per m²
Camden£67,000 to £124,000£3,100 to £5,150 build cost per m²£49,000 to £95,000£3,650 to £6,150 build cost per m²£69,000 to £127,000£1,950 to £3,300 build cost per m²
Croydon£58,000 to £109,000£2,650 to £4,450 build cost per m²£43,000 to £84,000£3,150 to £5,300 build cost per m²£60,000 to £111,000£1,700 to £2,850 build cost per m²
Ealing£61,000 to £114,000£2,800 to £4,700 build cost per m²£45,000 to £87,000£3,300 to £5,600 build cost per m²£63,000 to £116,000£1,800 to £3,000 build cost per m²
Enfield£60,000 to £111,000£2,750 to £4,550 build cost per m²£44,000 to £85,000£3,200 to £5,450 build cost per m²£61,000 to £113,000£1,750 to £2,900 build cost per m²
Greenwich£61,000 to £114,000£2,800 to £4,700 build cost per m²£45,000 to £87,000£3,300 to £5,600 build cost per m²£63,000 to £116,000£1,800 to £3,000 build cost per m²
Hackney£64,000 to £119,000£2,950 to £4,900 build cost per m²£47,000 to £91,000£3,450 to £5,900 build cost per m²£66,000 to £121,000£1,900 to £3,150 build cost per m²
Hammersmith and Fulham£67,000 to £124,000£3,100 to £5,150 build cost per m²£49,000 to £95,000£3,650 to £6,150 build cost per m²£69,000 to £127,000£1,950 to £3,300 build cost per m²
Haringey£63,000 to £117,000£2,900 to £4,800 build cost per m²£46,000 to £90,000£3,400 to £5,750 build cost per m²£65,000 to £119,000£1,850 to £3,100 build cost per m²
Harrow£60,000 to £111,000£2,750 to £4,550 build cost per m²£44,000 to £85,000£3,200 to £5,450 build cost per m²£61,000 to £113,000£1,750 to £2,900 build cost per m²
Havering£57,000 to £107,000£2,600 to £4,350 build cost per m²£42,000 to £82,000£3,050 to £5,200 build cost per m²£58,000 to £109,000£1,650 to £2,800 build cost per m²
Hillingdon£58,000 to £109,000£2,650 to £4,450 build cost per m²£43,000 to £84,000£3,150 to £5,300 build cost per m²£60,000 to £111,000£1,700 to £2,850 build cost per m²
Hounslow£61,000 to £114,000£2,800 to £4,700 build cost per m²£45,000 to £87,000£3,300 to £5,600 build cost per m²£63,000 to £116,000£1,800 to £3,000 build cost per m²
Islington£67,000 to £124,000£3,100 to £5,150 build cost per m²£49,000 to £95,000£3,650 to £6,150 build cost per m²£69,000 to £127,000£1,950 to £3,300 build cost per m²
Kensington and Chelsea£70,000 to £130,000£3,250 to £5,400 build cost per m²£52,000 to £99,000£3,800 to £6,450 build cost per m²£72,000 to £132,000£2,050 to £3,450 build cost per m²
Kingston upon Thames£63,000 to £117,000£2,900 to £4,800 build cost per m²£46,000 to £90,000£3,400 to £5,750 build cost per m²£65,000 to £119,000£1,850 to £3,100 build cost per m²
Lambeth£64,000 to £119,000£2,950 to £4,900 build cost per m²£47,000 to £91,000£3,450 to £5,900 build cost per m²£66,000 to £121,000£1,900 to £3,150 build cost per m²
Lewisham£61,000 to £114,000£2,800 to £4,700 build cost per m²£45,000 to £87,000£3,300 to £5,600 build cost per m²£63,000 to £116,000£1,800 to £3,000 build cost per m²
Merton£61,000 to £114,000£2,800 to £4,700 build cost per m²£45,000 to £87,000£3,300 to £5,600 build cost per m²£63,000 to £116,000£1,800 to £3,000 build cost per m²
Newham£60,000 to £111,000£2,750 to £4,550 build cost per m²£44,000 to £85,000£3,200 to £5,450 build cost per m²£61,000 to £113,000£1,750 to £2,900 build cost per m²
Redbridge£58,000 to £109,000£2,650 to £4,450 build cost per m²£43,000 to £84,000£3,150 to £5,300 build cost per m²£60,000 to £111,000£1,700 to £2,850 build cost per m²
Richmond upon Thames£66,000 to £122,000£3,050 to £5,050 build cost per m²£49,000 to £93,000£3,550 to £6,050 build cost per m²£68,000 to £124,000£1,950 to £3,250 build cost per m²
Southwark£64,000 to £119,000£2,950 to £4,900 build cost per m²£47,000 to £91,000£3,450 to £5,900 build cost per m²£66,000 to £121,000£1,900 to £3,150 build cost per m²
Sutton£58,000 to £109,000£2,650 to £4,450 build cost per m²£43,000 to £84,000£3,150 to £5,300 build cost per m²£60,000 to £111,000£1,700 to £2,850 build cost per m²
Tower Hamlets£64,000 to £119,000£2,950 to £4,900 build cost per m²£47,000 to £91,000£3,450 to £5,900 build cost per m²£66,000 to £121,000£1,900 to £3,150 build cost per m²
Waltham Forest£60,000 to £111,000£2,750 to £4,550 build cost per m²£44,000 to £85,000£3,200 to £5,450 build cost per m²£61,000 to £113,000£1,750 to £2,900 build cost per m²
Wandsworth£66,000 to £122,000£3,050 to £5,050 build cost per m²£49,000 to £93,000£3,550 to £6,050 build cost per m²£68,000 to £124,000£1,950 to £3,250 build cost per m²
Westminster£70,000 to £130,000£3,250 to £5,400 build cost per m²£52,000 to £99,000£3,800 to £6,450 build cost per m²£72,000 to £132,000£2,050 to £3,450 build cost per m²

The job priced in each column: house extension is a single-storey rear extension; side-return extension is a side-return extension; loft conversion is a loft conversion with a rear dormer.

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How to cite this index

Cost My Extension, London extension and loft cost index, 20 October 2026, costmyextension.co.uk/london-extension-cost-index

You are welcome to quote the figures with that credit. The CSV file carries the same attribution on its last line.

This report is an informed estimate built from public data about your property and current London build costs. It is not a survey, a quote, a valuation or planning advice. Always get written quotes and, where noted, professional advice before committing to work.