Building cost in Kensington & Chelsea: 2026 rates.
Building work in Kensington & Chelsea costs more than the London average because of heritage constraints, restricted site access and the borough's basement policy. A typical rear extension is £3,800–£5,200/m² on 2026 rates; a single-storey loft is £95k–£180k; basement excavation runs £6,000–£9,500/m². Costed runs an independent cost expert brief, pre-build budget, builder quote review, monthly monitoring.
| Project type | Typical 2026 cost |
|---|---|
| Rear extension | £3,800–£5,200/m² |
| Loft conversion (total) | £95,000–£180,000 |
| Full refurbishment | £3,200–£4,800/m² |
| Basement (per m²) | £6,000–£9,500/m² |
All figures exclude VAT (20% on most refurb/extension work), professional fees (8–14% typical), party wall awards and statutory costs.
- Stucco terraces and Grade II listings drive specification cost, heritage windows and lime mortar are non-negotiable
- RBKC's Basement Planning Policy CL7 limits single-storey basements under listed buildings and restricts excavation under gardens
- Most streets in SW3, SW7 and W8 sit inside a conservation area, material like brick, lead and slate must match
- Party Wall Act 1996 surveyor fees in K&C typically run £1,200–£3,500 per adjoining owner
- Builder quotes for K&C properties vary by 18–35% on the same scope, comparison saves more than the cost expert fee
Heritage scrutiny, Article 4 directions and basement policy CL7 are the cost-and-programme drivers. Independent cost monitoring catches preliminaries inflation early.
Frequently asked, Kensington & Chelsea
How much does a side return extension cost in Kensington & Chelsea?
A side return extension on a typical 4–5m wide K&C terrace costs £85,000–£140,000 on 2026 rates, plus VAT, fees and statutory costs. Cost per m² is higher than London average because of restricted site access, conservation-grade glazing and party wall complexity on stucco terraces.
Do I need planning permission for a loft conversion in Kensington & Chelsea?
Most K&C loft conversions need full planning permission. Permitted development rights are restricted across the borough's 38 conservation areas, Article 4 directions remove PD for many roof alterations. Mansard conversions usually require both planning and listed building consent on protected streets.
How long does a typical refurbishment take in Kensington & Chelsea?
A full strip-out and reinstatement of a 200m² K&C townhouse runs 9–14 months on programme. Heritage approvals, restricted delivery hours under RBKC's Code of Construction Practice and basement engineering all extend programme versus outer London.
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