Flat Conversions Harrow

Flat conversions in Harrow start from the borough's houses, which make up 62% of its homes. Splitting a house into self-contained flats always needs planning permission, and Local Plan Policy HO2 only allows it where the original internal floor area exceeds 130 square metres, or the house can acceptably be extended to that size. We build the approved scheme: new stairs and partitions, separate services for each flat, and the fire and sound separation between homes that the regulations require.

In Harrow, 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 Harrow: 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 Harrow houses Policy HO2 allows to become flats

Policy HO2 limits which Harrow houses can be split into self-contained flats, and floor area is the first test. The original internal floor area must exceed 130 square metres, or the house must be capable of being acceptably extended to that size. The site must also be in an area of PTAL 3 to 6, so a large house far from a station or bus corridor may not qualify at all.

The policy also shapes the finished building. A conversion must include at least one family home of at least 74 square metres, capable of being a 3 bedroom 4 person dwelling with a dedicated rear garden, which usually means the ground floor keeps the garden. Wherever possible a single front door is retained on the front elevation, so the new flats share an entrance hall. The new stair, meters and bin store are then arranged around that one door.

Housing in Harrow

The valuation list shows roughly 96,870 homes in Harrow, of which 10% are pre-1919, 52% interwar and 38% post-1945, split 38% flats to 62% houses. Semi-detached houses make up 31% of homes here, and the side of a semi in Harrow is where a separate entrance for the upper flat is most often placed.

London Plan space standards for each new Harrow flat

Each new flat in a Harrow conversion must meet the London Plan minimum internal space standards, because Policy HO2 requires it and the London Plan counts conversions as new dwellings. A one-bedspace single bedroom must be at least 7.5 square metres and 2.15m wide, a double at least 11.5 square metres, and at least 75 per cent of each flat needs a floor to ceiling height of 2.5m. Those figures decide how many flats a house can hold.

Ceiling height is where interwar Harrow houses can lose a unit on paper. The first floor may pass while a room in the roof does not reach 2.5m over enough of its area, so the top flat shrinks or becomes part of the flat below. Dual aspect layouts are preferred under the London Plan, and single aspect flats are normally avoided, which favours front to back flats over a split down the middle. The owner's designer resolves this before the application, and we check it against the survey.

Fire and sound separation between flats in a Harrow house

A house becoming flats is a material change of use, so the building regulations apply to the whole building, not only the new parts. Under Part E, Approved Document E sets sound insulation for flats formed by change of use at 43 dB airborne for walls and for floors and stairs, and 64 dB maximum impact for floors and stairs. In a Harrow house with a timber first floor, that means new ceilings on resilient bars, mineral wool in the void and sealed edges before any flooring goes down.

Fire separation between flats, a protected stair to the front door and self-closing fire doors to each flat come under Part B. We arrange pre-completion sound testing once the separating walls and floors are complete, before decoration, so any failure is fixed while it is still cheap to reach. Harrow Building Control individually determines its charges for converting over 10 homes, or for dwellings over three storeys or over 300m2, so larger schemes get a bespoke quote from the council.

Services, basements and the reverse conversion in Harrow

Each Harrow flat needs its own electricity supply and meter, its own heating, and usually its own gas or an all-electric system, plus a postal address from the council's street naming and numbering service. Meter positions are agreed with the suppliers early, because a new supply can take longer than the building work. Where walls shared with the neighbouring house are cut into or built on, the building owner serves notice under the Party Wall Act, and those works start only on the neighbour's written consent or under an award.

Harrow Local Plan Policy GR4A says basement proposals for self-contained homes will not be supported, so a basement flat is not a route to an extra unit. Going the other way, combining flats back into one Harrow house is physically the reverse of a conversion: extra kitchens come out, meters are merged and the shared hall is opened back up. Because the number of homes falls, settle with the council first whether planning permission is needed before the strip-out begins.

• New soil stacks, wastes and bathrooms stacked floor over floor
• Pre-completion sound testing arranged before sign-off
• Flats converted back into a single family house

VOA Council Tax stock of properties, March 2025, for all 30 statistical areas in Harrow. Counts rounded by the VOA.

When comparing flat conversions in Harrow with other work, it helps to read structural alterations in Harrow, our Harrow area guide, builders in London who take on conversions, renovations across London, how we handle flat conversions across London and Structural Engineer Report Cost.

Why Harrow Homeowners Choose GS Renovation

A conversion runs on its approvals, so we start by reading the planning consent and the building control drawings side by side with the owner's designer. We then programme strip-out, structure, new stair and partitions, fire and sound separation, services for each flat, testing and finishes. We fit any steel to the structural engineer's design, a registered electrician certifies the wiring in each flat, and you get the sound test results and certificates at handover.

• Fire strategy for the stair and each flat entrance settled before strip-out
• Mains-wired, interlinked smoke and heat alarms to the approved fire strategy
• Neighbours given notice before the noisy stages

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.