Flat Conversions Hounslow

Converting a house into self-contained flats in Hounslow starts with one number. Local Plan Policy SC6 expects a house to have a minimum 130sqm net original internal floor area before it is considered suitable for conversion, and at least one family-sized unit of two bedrooms and four persons or more at ground floor. Planning permission is needed every time. After that the work is about separating homes: fire and sound between floors, separate services and meters, and rooms that meet the London space standards.

In Hounslow, 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 Hounslow: 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.

Is your Hounslow house big enough to convert into flats?

The test is the original house, not the house as it stands today. Policy SC6 sets a minimum 130sqm net original internal floor area for a house to be considered suitable for conversion or subdivision. Hounslow will not support converting a house that only reaches 130sqm because it was previously extended or had outbuildings added. A rear extension or garden room built last year does not count towards the threshold.

That can rule out the smaller houses. Terraced houses make up 26% of Hounslow's homes and semi-detached or detached houses 23%, and a small two storey terrace or interwar semi may fall short of 130sqm of original floor. The candidates are the larger houses, such as a big Victorian house near the river among the 16% built before 1919. Measure the original floor area from old plans or a survey before paying for a design, and have your designer or agent make the planning application.

Housing in Hounslow

Around 111,270 homes make up Hounslow on the valuation list; 50% are flats and 50% houses, and 16% date from before 1919, 28% from between the wars and 55% from after 1945. Terraced houses make up 26% of homes here, and a converted terrace in Hounslow has two party walls to consider for sound.

Space standards for each new Hounslow flat

Each flat created in Hounslow must meet the London space standards, because the London Plan table says a new dwelling includes conversions and change of use. Hounslow's Local Plan asks that new housing complies with the Nationally Described Space Standard. Under Policy D6 a single bedroom must be at least 7.5 square metres and at least 2.15m wide. A double or twin bedroom must be at least 11.5 square metres. The standard sits in the planning system rather than building regulations, so it is settled at the design stage.

Height and aspect catch older houses out. Policy D6 sets a minimum floor to ceiling height of 2.5m for at least 75 per cent of the Gross Internal Area of each dwelling, and new acoustic ceilings take height out of every room. Policy D6 also asks to maximise dual aspect homes and normally avoid single aspect ones, which is hard for a rear flat in a narrow terrace. We measure the existing heights on site so your designer can check the layout before it is submitted.

Fire and sound separation between the Hounslow flats

Separating one home from another is the core of the building work in a Hounslow conversion. Under Part B the floors between flats, the walls to the common stair and each flat's entrance door must resist fire for the period on the approved plans, with fire stopping at every pipe and cable that passes through. The common stair becomes a protected escape route, with linked alarms and emergency lighting. Hounslow's building control says a full plans application is usually used for a change of building use.

Sound is the other half. Approved Document E sets lower sound insulation performance for flats formed by material change of use: 43 dB airborne for walls and for floors and stairs, and 64 dB maximum impact for floors and stairs. In an old timber floor that usually means an independent ceiling, acoustic quilt between the joists and a resilient floating floor above. A pre-completion sound test proves the result, so we build the separating floors to the specified detail before the test.

Services, addresses, neighbours and turning Hounslow flats back

Every flat in a Hounslow conversion needs its own supplies and address. That means separate electricity meters and consumer units, a separate water supply or sub-meter, separate heating, and new addresses through the council's street naming and numbering service before the utilities will connect. Where the conversion cuts into a party wall or builds on it, the building owner serves notice on the neighbour under the Party Wall Act. Hounslow charges building control on a house into two flats with an added charge for each further flat.

The reverse also happens. Joining flats back into one house removes homes, so it can need planning permission, and many London boroughs resist the loss of homes. Your designer checks before anything is stripped. A house into flats is never permitted development. On 4 March 2025 Hounslow also confirmed an Article 4 direction removing certain permitted development rights that would result in new dwellings, so check it before relying on any permitted route to new homes. We build to the approved plans and conditions.

• Full plans building control applications coordinated for you
• Separating walls built and lined for sound between flats
• Splitting a large flat in two, or joining two flats into one

VOA Council Tax stock of properties, March 2025, for all 29 statistical areas in Hounslow. Counts rounded by the VOA.

When comparing flat conversions in Hounslow with other work, it helps to read structural alterations in Hounslow, our Hounslow area guide, a building contractor for the whole conversion, the Party Wall Act when a conversion cuts a shared wall, how we handle flat conversions across London and How to Choose a Builder.

The GS Renovation Difference in Hounslow

A conversion has many stages and inspections, and the order matters. We take the build from strip out through structural work, fire and sound separation, new services and meters, to finished flats ready for the completion certificate. A structural engineer designs any steel for new openings or stairs, and we build to that design. You get a written programme showing each inspection, the sound test and each certificate, so the sale or letting of the flats can be planned against real dates.

• Full plans application to building control, never a building notice
• Site left safe and secure at the end of every day
• Wet rooms stacked floor over floor to keep the drainage simple

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.