Basement conversion in Mill Hill

Investigate the structure and ground before design.

Start with the basement conversion brief

Distinguish an existing cellar conversion from excavation for a new basement. Record levels, drainage, access and the adjoining structures, and obtain project-specific ground and structural investigations before relying on a design or budget.

Plan temporary works, waterproofing, ventilation, escape and spoil removal as part of the same brief. Ask Hampstead Chartered Surveyors to assess party-wall matters and Hampstead Architecture & Planning to coordinate the design requirements. An area name alone does not establish ground conditions.

The local building context

Barnet’s Mill Hill Conservation Area Character Appraisal Statement, adopted in April 2008, places the conservation area towards the north-west corner of the borough: about 152 hectares, with institutional buildings and houses strung out for a mile along the high ground of The Ridgeway, looking over Green Belt countryside from Burtonhole Lane to the south-east and Marsh Lane to the north. It counts approximately 260 houses, brick and weatherboard cottages typical of rural Middlesex among a large number of rambling institutional buildings, with three clusters of smaller houses and cottages along The Ridgeway.

The appraisal’s principal building types include timber-framed buildings from the late sixteenth century onwards, largely remodelled in brick or white or black weatherboard, with clay-tiled roofs, timber casements or sashes and low picket fences; Rosebank and Rosebank Cottage on The Ridgeway, a seventeenth-century timber-framed building, is listed at grade II. Small weatherboard and brick cottages of the mid-eighteenth to nineteenth century are another, such as the late eighteenth-century weatherboarded cottages on Hammers Lane, also grade II. Early timber-framed roofs are pitched at about 45 degrees in handmade clay tiles; most buildings after the mid-nineteenth century have Welsh slate.

Mill Hill Village, a cluster of small vernacular dwellings at the top of Milespit Hill, is mainly two-storey late Victorian development in brick under slate or tile, or render under tile, behind white-painted picket fences. Wills Grove and Winterstoke Gardens have early twentieth-century Arts and Crafts houses in red brick and tile, with roughcast or brick walls, steep roofs, timber casements, prominent chimneys and hedged boundaries. By 2008 some former Mill Hill School boarding and staff houses on Wills Grove were private houses and apartments, and the appraisal records John Laing’s 1933 Sunnyfields Estate where Lawrence Street meets Highwood Hill.

Local design and consent context

Planning data records the Mill Hill Conservation Area, reference CA13, as a London Borough of Barnet designation dating from December 1968, and Barnet’s Character Appraisal Statement is marked adopted in April 2008. The appraisal divides the area into six character areas: Nan Clarks Lane and Highwood Hill; The Forge and Lawrence Street; The Ridgeway; the Three Hammers T-junction; Mill Hill Village; and Wills Grove and Winterstoke Gardens, with the planned development of Hammers Lane.

On its open data portal, Barnet presents its conservation area appraisals and boundary maps as the authoritative source. The published Mill Hill boundary map, dated November 2023, gives a last amended date of 26 September 1988. The appraisal describes the area as it was in 2008, when Barnet consulted a Mill Hill Conservation Area Advisory Committee on applications affecting it.

A separate Article 4(2) direction, whose map outlines the Retail Trust Cottages on both sides of Hammers Lane, controls specified householder works that would front a highway, waterway or open space, and the erection, alteration or removal of chimneys. The order is marked approved on 24 April 2008, but planning data starts it on 15 January 2007, so confirm the details with Barnet. Mill Hill Cemetery has a direction of its own covering gates, fences, walls and other means of enclosure.

Access and site planning

At a Barnet address, the council publishes construction working hours for noisy work: Monday to Friday, 8am to 6pm; Saturday, 8am to 1pm; and none on a Sunday or bank holiday. Stricter terms on noise, deliveries and common parts may come from a lease, a managing agent or the building’s own rules. Living at home through the work means agreeing which rooms stay in use and when water or power will be off, and neighbours, including anyone who shares a drive, stair or private road, should hear in advance what is planned.

Continue planning

The Mill Hill area guide · Basement conversion across London · Hampstead Architecture & Planning · Hampstead Chartered Surveyors

Discuss your project

Tell us what you are planning in Mill Hill

Share the property location, the work you have in mind and any drawings or permissions you already have.

£5M public liability, £10M employers’ liability and contractors’ all risks cover.

Design support: Hampstead Architecture & Planning.
Surveying support: Hampstead Chartered Surveyors.