House Extensions & Loft Conversions in Islington

LCCL Construction is a design and build company based in Finchley N3, working in Islington for over 20 years. One team, one contract: architects, structural engineers, project managers and builders coordinated by LCCL take your project from first sketch to handover.

Islington is Georgian and Victorian terraces — Barnsbury, Canonbury, Highbury — usually in flats or narrow houses. Rear extensions, mansard roofs where policy allows, basements and full renovations are the projects; every one is a party wall job.

What it costs in Islington

The final figure depends on postcode, access and site conditions — the instant estimate applies your area. Guide ranges for 2026, design and build inclusive (architecture, structural engineering, planning or LDC, construction, project management and building control). Every project is surveyed and priced individually.

• Velux loft: £32,400 – £50,400 inc. VAT (£27,000 – £42,000 + VAT)
• Rear dormer loft: £56,400 – £80,400 inc. VAT (£47,000 – £67,000 + VAT)
• L-shaped dormer: £58,800 – £98,400 inc. VAT (£49,000 – £82,000 + VAT)
• Hip to gable: £60,000 – £114,000 inc. VAT (£50,000 – £95,000 + VAT)
• Mansard: £76,800 – £148,800 inc. VAT (£64,000 – £124,000 + VAT)
• 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)

Kitchen on top of the structure, supplied and fitted: +£9,000 – £87,360 inc. VAT (£7,500 – £72,800 + VAT) depending on size and specification. Basements: cellar refit £54,000 – £114,000 inc. VAT (£45,000 – £95,000 + VAT), lowering £114,000 – £216,000 inc. VAT (£95,000 – £180,000 + VAT), new dig £216,000 – £360,000 inc. VAT (£180,000 – £300,000 + VAT)+. New build: £2,200 – £4,500 per sqm (zero-rated for VAT).

Recent LCCL projects near Islington

Grosvenor Avenue, Highbury N5 — rear extension through Islington planning

An Edwardian terrace in Highbury with a single-storey rear extension: a new kitchen and dining space under a roof lantern with underfloor heating and doors to a landscaped garden, taken through Islington planning with the drainage changes the planners asked for and a party wall agreement on one side.

See the project

Also nearby: Uplands Road, Crouch End N8 (double-storey extension, 2023) · Princess Road, Primrose Hill NW1 (renovation, 2025).

Planning in Islington

Islington is one of the stricter boroughs: conservation areas cover most of it, mansards are only accepted where the terrace already has them, and pre-application advice is less forthcoming than in outer boroughs. A precedent-led application works best.

Permitted development in Islington: what goes ahead without a planning application

Mostly a planning application. Islington has Article 4 directions in 40 of its 42 conservation areas and guidelines that rule out most visible roof extensions, so most Islington projects go through a householder application, which we handle. On the streets outside the conservation areas, a rear dormer or a 3 m rear extension still goes ahead without one. Flats and maisonettes have no permitted development rights, whatever the street, and inside any conservation area a dormer or roof enlargement needs a planning application even where a single-storey rear extension within the limits does not.

On a house outside those streets, a rear dormer loft (40 m³ on a terrace, 50 m³ on a semi or detached house), a hip-to-gable, a single-storey rear extension of 3 m (4 m on a detached house) and a side-return infill are permitted development, and we apply for a Lawful Development Certificate on every one so the position is confirmed in writing. See our fixed-price permitted development projects — from £32,400 inc. VAT (£27,000 + VAT) for a Velux loft and £42,000 inc. VAT (£35,000 + VAT) for a 3 m rear extension, design and build inclusive, postcode dependent. Not sure whether your project needs a planning application? Planning check

Conservation areas and Article 4 directions in Islington

Islington has 42 conservation areas and Article 4 directions in 40 of them, controlling replacement windows and doors, the painting of brickwork and other front-facing changes. The ones we work in most are Barnsbury (late-Georgian and early-Victorian squares), Canonbury (semi-detached mid-Victorian villas with large gardens), Highbury Fields, Highbury New Park (1850s detached and semi-detached houses), Tufnell Park and Whitehall Park on the Archway side (large three-storey late-Victorian red-brick terraces). The council’s conservation area design guidelines (2002) are specific: full-width rear extensions above one storey, or half-width extensions above two storeys, are not normally permitted; Barnsbury allows no roof extension visible from the street except on scheduled properties, accepts mansards only on scheduled buildings and refuses front and side dormers; Canonbury refuses front and side dormers and rooflights and limits side extensions to 3 m high set back 3 m; Whitehall Park has a presumption against roof extensions altogether. Front basement areas must not be infilled, and the council’s own FAQ confirms that a roof extension in a conservation area always needs planning permission.

Basements

Local Plan policy DH4 (adopted 28 September 2023) and the Basement Development SPD (January 2016) allow a single storey below the lowest original habitable floor, no more than 3 m floor to ceiling, covering less than half the original garden and no more than the original footprint, with at least 1 m of soil plus a 200 mm drainage layer over any part of the basement beyond 3 m of the rear wall. A Structural Method Statement by a qualified engineer accompanies every application.

Fees and timescales

A householder application costs £548 (from April 2026, plus the Planning Portal charge) and Islington has eight weeks to decide it. Formal pre-application advice (from 2 January 2025) is £480 written, £700.80 with a site visit or £1,440 for a listed building, with a 30-working-day response — which is why a precedent-led application is often the better route. Islington sets no numerical daylight rule; we design to the 45-degree line as standard. Party wall notices run alongside planning: two months’ notice for works to a shared wall, one month for excavations within 3 m or 6 m of a neighbour’s foundations.

Building control

Islington runs its own building control service and is an LABC member. We use the council inspector on every project. Typical inspection points are commencement, foundation trenches, oversite and damp-proof course, drainage before backfill, structural steels and joists before they are covered, insulation and fire-stopping before plastering, then completion. We book each one and hand you the completion certificate at the end of the job.

Anderson's advice: use pre-application advice where the council engages

Wandsworth planning is much more helpful on pre-application than Islington in our experience. Where a council engages, a pre-app saves weeks; where it does not, a well-argued application with precedent cases works better.

What our clients say

“The Lccl construction team built my extension with a quick and clean service, they worked non stop through the winter weather.. I would highly recommend this company!”

— Chris Dunn, Google Reviews

As LABC Building Excellence Award winners in 2024 (Best Residential Extension in London) and 2026 (Best Conversion or Alteration to an Existing Home, Weech Road NW6), every project is delivered by one team of architects, structural engineers, project managers and builders. Workmanship is guaranteed for 12 months from practical completion, with a 10-year LABC structural warranty.

Nearby areas

Islington is part of our Central London guide. Nearby areas: Camden, Kensington & Chelsea, Notting Hill.

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

One team, one contract, one point of contact — from first sketch to handover.