Flat Conversions Hillingdon

Converting a house into flats in Hillingdon is tightly controlled, and planning permission always comes first. Under Policy DMH 4 the original house needs at least 120 sqm of internal floor area, each floor can hold one flat only, and no scheme is supported that would take more than 10% of properties on the street into flats. Houses are 66% of Hillingdon's homes, but each one has to be measured against that size test before anything is drawn. We build approved conversions, with the fire separation and sound insulation between flats built to Parts B and E.

In Hillingdon, converting a house into two or three flats is published at £50,000 to £120,000 including professional and council fees, and an England-wide guide puts a straightforward two-flat split at £40,000 to £80,000 in construction alone, which is the part a builder prices (indicative London ranges, Architectural Drawings and Mayfair Studio, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Hillingdon: we build the conversion to the approved drawings, building control inspects the fire and sound separation, and a registered electrician certifies each flat's electrics.

Which Hillingdon houses can be split into flats

The first test in Hillingdon is size. Policy DMH 4 sets 120 sqm as the smallest original internal floor area it will accept for a conversion, and one flat per floor as the ceiling. It also sets a street cap: a scheme is not supported if it would take more than 10% of properties on that residential street into flats. Count the converted houses on your street before paying for drawings, because a street at that share can stop a scheme however good the layout is.

The stock narrows the field further. The VOA count puts 37% of Hillingdon homes in the interwar years and 36% in the semi-detached or detached group, and a two storey interwar semi can sit close to the size threshold rather than comfortably over it. Measure the original house, leaving out later extensions, before commissioning a designer. Larger detached houses and the few pre-1919 houses are the likelier candidates, and the policy then allows a flat on each floor.

Housing in Hillingdon

The valuation list shows roughly 118,240 homes in Hillingdon, of which 4% are pre-1919, 37% interwar and 59% post-1945, split 34% flats to 66% houses. 27% of homes here are semi-detached; the side of a semi in Hillingdon is where a separate entrance for the upper flat is most often placed.

Self-contained flats and family homes under Hillingdon policy

Policy DMH 1 adds that each unit has to be self contained, with its own kitchen, bathroom and entrance. On a Hillingdon house large enough to pass the size test, the clearest layout keeps the ground floor flat on the original front door. The upper flat gets a second door and an enclosed stair, which takes space from the hall. Draw that entrance arrangement first, because it fixes where the upper kitchen and bathroom can sit over the rooms below.

Hillingdon's housing evidence points to a substantial requirement for larger units, particularly three bedroom homes, so a scheme that keeps a family-sized flat on the ground floor answers that need better than two small units. The London Plan counts residential conversions as incremental intensification where they add net housing. The reverse, turning flats back into one house, loses a home, so the owner and designer check the planning position before any de-conversion is priced.

Space standards for Hillingdon flat conversions

Hillingdon Policy DMHB 16 holds every conversion to the current internal space standards as a minimum, and the London Plan treats a conversion as a new dwelling. London Plan Policy D6 puts a single bedroom at 7.5 sq m and 2.15m wide or more, and a double at 11.5 sq m or more. At least 75 per cent of each flat's floor area needs 2.5m from floor to ceiling. On a house with low upper ceilings, that height rule can decide which floor takes the living space.

These standards sit solely within the planning system, not in the building regulations, so they are settled on the drawings before planning is sought. Policy D6 also asks for private outdoor space of at least 5 sq m for a one or two person flat where the borough sets no higher figure, and it favours dual aspect homes. In a Hillingdon semi, the upper flat's outdoor space is the hard part, which is why the garden split is drawn early.

Fire, sound, services and party walls in a Hillingdon conversion

Between the flats, the separating floor and any separating wall have to meet Building Regulations Parts B and E. For flats made by a change of use, Approved Document E asks walls and floors to reach 43 dB of airborne sound insulation, and floors to let through no more than 64 dB of impact sound. In a Hillingdon semi with timber joists, that normally means a new ceiling on resilient bars, acoustic insulation between the joists and a floating floor above, plus fire-resisting construction and a protected stair.

Each flat needs its own services: a separate electricity meter and consumer unit, its own gas supply or electric heating, and a water supply that can be isolated. The owner applies to the council for street naming and numbering so each flat has an address for the utilities. Where the work cuts into a party wall, the building owner serves notice, and where the neighbouring house is council owned, the Hillingdon notice goes to the Mayor and Burgesses of the borough.

• Steel beams and new openings built to the engineer's design
• House to flat conversions into two or more self-contained units
• Separating walls built and lined for sound between flats

VOA Council Tax stock of properties, March 2025, for all 32 statistical areas in Hillingdon. Counts rounded by the VOA.

Work in Hillingdon rarely sits on its own, so you may also want structural alterations in Hillingdon, our Hillingdon area guide, builders in London who take on conversions, refurbishing a flat that has already been converted, flat conversions across London and How to Choose a Builder.

Why Choose GS Renovation in Hillingdon

Owners and developers in Hillingdon use GS Renovation for a flat conversion when they want the builder to follow the approved scheme closely. We read the planning consent and the building regulations drawings before we price, then give you a written quote after a site visit and a written programme. Your structural engineer designs any new openings or steel, and we build to that design. The founder, Abdelaaziz Saaid, oversees the separating floors and walls where acoustic and fire failures show up, and we arrange the pre-completion sound testing.

• Structural engineer instructed and coordinated on your behalf
• Mains-wired, interlinked smoke and heat alarms to the approved fire strategy
• Each flat's new electrics signed off by a registered electrician for Part P

Checked by Abdelaaziz Saaid, founder and director of GS Renovation Ltd (Companies House no. 14611254). Structural design is by the consulting engineer appointed to your project.