Building cost in Islington: 2026 rates.
Islington's Georgian and Victorian terrace stock drives a clear cost band, rear extensions £3,000–£4,200/m², loft conversions £70k–£135k, full refurbs £2,500–£3,700/m² on 2026 rates. Restricted street parking, narrow side returns and party wall density mean preliminaries and access costs run 12–18% of the contract sum, ahead of outer-London norms.
| Project type | Typical 2026 cost |
|---|---|
| Rear extension | £3,000–£4,200/m² |
| Loft conversion (total) | £70,000–£135,000 |
| Full refurbishment | £2,500–£3,700/m² |
| Basement (per m²) | £5,000–£7,800/m² |
All figures exclude VAT (20% on most refurb/extension work), professional fees (8–14% typical), party wall awards and statutory costs.
- Islington's Basement Development SPD limits depth and forbids basements under listed terraces
- Barnsbury, Canonbury, Highbury and Clerkenwell conservation areas remove most PD rights
- Side-return extensions are the dominant kitchen typology, pricing varies 20–30% on the same brief
- Party Wall Act 1996 awards typically cost £1,000–£2,800 per adjoining owner
- Skip permits, suspension of bays and crane lifts in N1 add £8k–£20k of preliminaries on a major refurb
Islington quote markets are competitive, line-by-line quote review usually finds 10–18% of saveable cost.
Frequently asked, Islington
How much does a side return extension cost in Islington?
A 12–18m² side return on an Islington Victorian terrace costs £65,000–£105,000 on 2026 rates, plus VAT, design fees, party wall awards and statutory costs. Cost variation is driven by glazing spec, structural opening size and the choice between in-situ and pre-cast steel.
How long does a loft conversion take in Islington?
An Islington loft conversion typically takes 10–14 weeks on site from strip-out to handover, plus 2–4 weeks of pre-start mobilisation and party wall notice. Mansard conversions add 3–6 weeks for planning and roof reconstruction.
Is planning permission needed for an Islington rear extension?
A single-storey rear extension up to 4m deep on a detached house or 3m on a terrace can often go under permitted development, but most Islington conservation areas (Article 4) remove that right. Check the borough's Article 4 schedule before assuming PD.
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