House Extensions Islington N1 2026: Complete Guide to Costs, Planning and Design

Islington is one of London's most prestigious and sought-after inner London boroughs for house extensions. The London Borough of Islington has exceptionally high property values, a high concentration of Georgian and Victorian terraced houses and extensive conservation area coverage — making house extensions both technically demanding and financially outstanding. On our projects and local sold prices, a well-planned project of this kind usually adds more to the value of the home than it costs to build — see our guide on how much value an extension adds. LCCL Construction delivers house extensions across Islington as part of our complete design and build service.

LCCL Construction — specialist house extension builders in Islington N1 and inner North London

House Extensions Islington N1: Best Types for Local Properties

Islington's Georgian and Victorian terraced houses are ideally suited to side return extensions, rear extensions and wraparound extensions. Many Islington terraces have a back addition alongside the rear — making the wraparound extension the outstanding choice for creating a large open plan ground floor. Double storey rear extensions are also popular in Islington for families who need space on both floors. Given the exceptional property values in N1, even a modest side return extension generates an outstanding return on investment.

How Much Do House Extensions Cost in Islington in 2026?

House extension costs in Islington are at the upper end of the London range.

Rear extension: £42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT).

Side return: £42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT).

Wraparound: £72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT).

Double storey: £90,000 – £198,000 inc. VAT (£75,000 – £165,000 + VAT).

All include architectural design, planning permission, building regulations, structural calculations, party wall agreements, construction and finishing.

See our full house extension cost guide.

Planning Permission for House Extensions in Islington

Planning permission in Islington is complex. The London Borough of Islington has one of the highest proportions of conservation area coverage in London — the Barnsbury, Canonbury, Highbury Fields, Mildmay and Thornhill Square conservation areas cover vast areas of N1. Within conservation areas planning permission is required for most extensions. LCCL Construction checks all planning requirements. See our guide to house extension planning permission in London.

How Much Value Does a House Extension Add in Islington?

Islington has some of the highest property values in inner London, with terraced houses regularly achieving £900,000 to £2,500,000. A wraparound extension costing £72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT) can add £180,000 to £350,000 to the value — a return of 180 to 350 per cent. See our guide on how much value a house extension adds in London.

Areas of Islington We Cover

LCCL Construction covers all areas of Islington including Angel N1, Barnsbury N1, Canonbury N1, Highbury N5, Holloway N7, Tufnell Park N7, Finsbury Park N4, Archway N19, Caledonian Road N1, Pentonville N1, Clerkenwell EC1, De Beauvoir Town N1 and all surrounding postcodes.

Frequently Asked Questions About House Extensions in Islington

How much does a house extension cost in Islington?

Costs range from £50,400 inc. VAT (£42,000 + VAT) for a small rear extension to £158,000 for a large double storey. A typical wraparound costs £72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT) in Islington.

Do I need planning permission for a house extension in Islington?

Most extensions in Islington N1 require planning permission due to conservation area coverage. LCCL Construction checks all planning requirements as part of the free consultation.

To get a free consultation call LCCL Construction on 020 8037 7332 or get an instant quote online.