House Extensions & Loft Conversions in Watford

LCCL Construction is a design and build company based in Finchley N3, working in Watford 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.

Watford, Bushey and Oxhey have 1930s semis and post-war houses with hipped roofs and reasonable plots — hip-to-gable lofts, rear dormers and rear or wraparound extensions.

What it costs in Watford

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).

A recent LCCL project near Watford

Lancaster Avenue, Hadley Wood EN4 — 3,033 sq ft luxury new build

A 3,033 sq ft detached house designed and built by our team from planning through to handover.

See the project

Planning in Watford

Watford Borough and Hertsmere (Bushey) are generally permissive under permitted development; Nascot, Oxhey and Bushey village conservation areas need planning permission for roof and front changes.

Conservation areas and Article 4 directions in Watford

Watford has ten conservation areas: Grove Mill Lane (1973), St Mary’s (1975), Nascot (2001, the Victorian and Edwardian suburb north of the town centre), The Square (2001), Estcourt (2001, extended 2010), Watford Heath (2001, extended 2008), Civic Core (2001), High Street/King Street (2006), Macdonnell Gardens (2011) and Oxhey (2013). Article 4 directions are street-specific within the residential areas — Nascot, Nascot Road, Civic Core and Watford Heath among them — and typically remove permitted development for extensions and alterations (Class A), roof changes facing the street (Class C), porches (Class D), fences and external painting. In any conservation area, roof extensions and dormers, rear extensions of more than one storey and side extensions need planning permission. The inter-war and post-war streets of WD18, WD19, WD24 and WD25 outside the conservation areas take lofts and rear extensions on a Lawful Development Certificate; Bushey and Oxhey Hall across the border fall under Hertsmere.

Extension size rules Watford applies

The Watford Local Plan 2021–2038 was adopted on 17 October 2022, and the Residential Design Guide SPD (2014, amended 2016) remains in force with clear numbers. Single-storey rear extensions are limited to 3 m on a terrace and 3.5 m on a semi-detached or detached house (paras 8.4.6, 8.5.1); two-storey rear extensions are unlikely to be accepted beyond 3 m (8.8.1–8.8.2). Side extensions are set back at least 1 m from the front building line, no wider than one third of the extended width, with the first floor at least 1 m from the side boundary (8.7c, 8.8.2). Dormers take up no more than half the roof height and width and sit at least 0.5 m below the ridge and above the eaves (8.12.3); front dormers are generally inappropriate in conservation areas. The guide also asks for 27.5 m back-to-back between houses, 11 m from upper habitable windows to the boundary, 10 m flank to flank, and gardens of 50, 65, 80 or 95 m² for one/two-, three-, four- and five-bedroom houses (7.3.15, 7.3.21, 8.4.7). Watford has no householder basement policy.

Light to neighbours

Watford writes the daylight test into its guide: an extension should not cross a 45-degree line from the centre of any neighbouring rear ground-floor habitable window, on plan and on elevation (7.3.11, 8.4.3), with a 25-degree test for buildings facing each other (7.3.12). We design to the lines from the first sketch.

Fees and timescales

A householder application costs £548 (from April 2026, plus the Planning Portal charge) with an eight-week decision period; Watford offers a written householder pre-application service with a four-week response. 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

Watford and St Albans run a shared building control service. We use the council inspector on every project and book each inspection from foundations to completion, handing you the completion certificate at the end of the job.

Anderson's advice: talk to your neighbours before the notices go out

Semi-detached hip-to-gable plus rear dormer combinations almost always fall under permitted development, but neighbours often object informally. A conversation over the fence before the party wall notice lands avoids most of it.

What our clients say

“LCCL Construction were professional from start to finish. The team were trustworthy, reliable and delivered work to the highest standard.”

— KashImaging, Trustpilot

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

Watford is part of our Hertfordshire guide. Nearby areas: St Albans, Potters Bar, Borehamwood.

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.