Flat Conversions Hayes

Converting a house into self-contained flats in Hayes always needs planning permission, and Hillingdon's Policy DMH 4 sets hard tests before design starts. The original building needs at least 120 sqm of internal floor area, conversions are limited to one unit per floor, and no more than 10% of properties on the street may become flats. With much of the housing here post-war family homes and 1930s semis, a two storey Hayes house may fall below the size test, so measuring it comes first.

In Hayes, 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 Hayes: 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 Hayes houses pass the conversion policy tests

The floor area test is the first filter, and it can rule a Hayes house out before any drawing is made. Hillingdon Policy DMH 4 requires the original building to have an internal floor area of at least 120 sqm. A two storey 1930s semi below that size cannot be split into flats under the policy, however the rooms are arranged. The policy measures the original building, so a later extension may not count towards the figure.

The street matters as well as the house. DMH 4 only permits conversions where no more than 10% of properties on the residential street would be redeveloped into flats. However large the house, a Hayes road that already has several conversions may be closed to more. Your designer counts the existing conversions on the road first, then commissions a measured survey of the house. We price and programme the build only once both checks show the scheme can proceed.

Housing in Hayes

Roughly 16,650 dwellings sit on the valuation list for Hayes. 58% are houses and 42% flats, and by age 4% predate 1919, 44% are interwar and 52% post-war. The side of a semi in Hayes is where a separate entrance for the upper flat is most often placed, and 30% of homes here are semi-detached.

Self-contained flats and space standards in a Hayes conversion

Every flat formed in a Hayes conversion has to be fully self-contained. Hillingdon Policy DMH 1 only permits subdivision where every unit has its own sanitary and kitchen facilities and its own entrance. Under DMH 4, conversions are limited to one unit per floor, so a two storey house gives two flats at most. A shared kitchen, a bathroom across the landing or a flat reached through another flat's hallway will not pass.

Policy DMHB 16 then requires conversions to meet or exceed the most up to date internal space standards, and London Plan Policy D6 sets the figures. A single bedroom needs at least 7.5 square metres and 2.15m of width, and a double at least 11.5 square metres. Each flat needs a floor to ceiling height of 2.5m over at least 75 per cent of its floor area. In a Hayes semi with modest ceilings, the height rule can decide the layout, so it is checked during the measured survey.

Sound and fire separation between flats in Hayes

The floors between flats in a Hayes conversion carry the heaviest building work. Approved Document E sets sound insulation for flats formed by material change of use at 43 dB airborne for walls, floors and stairs, and a 64 dB maximum for impact on floors and stairs. Pre-completion sound testing shows the result. On the timber floors of an interwar house that typically means a new ceiling below, insulation between the joists and a resilient layer above.

Fire separation goes in alongside the acoustic work. Part B asks for a fire-resisting floor between the flats, a protected escape stair and a fire door to each flat, with smoke detection in each dwelling. The services are split at the same stage: separate gas and electricity meters, a separate water supply where the supplier requires it, and new addresses through street naming and numbering. We build it all to the approved drawings so building control can sign off the conversion.

Turning converted flats in Hayes back into one family house

Returning flats to a single family house is also worth considering in Hayes. Hillingdon says its current housing need evidence points to a substantial requirement for larger units, particularly three bedroom properties. A converted interwar semi put back together can give exactly that. Because the change loses a home, your designer confirms whether planning permission is needed before any work is priced. Losing a dwelling is a planning matter in its own right, so allow time for an application in the programme.

De-conversion is a refurbishment in its own right. The second kitchen comes out, the staircase is reopened to the whole house and the separate services are joined, with the utility suppliers removing the extra meters. The fire doors and extra separation can often be simplified once only one household lives there, though your building control route should confirm it. The spare doorbells and letter boxes go last, and we plan the whole sequence as one programme.

• Bin stores, cycle stores and external works to the planning conditions
• Heating and hot water for each flat, gas by a Gas Safe registered engineer
• Common hallway, stair and entrance finishes

VOA Council Tax stock of properties, March 2025, for Hayes End, Hayes Town North, Hayes Town & Lake Farm and Hayes South. Counts rounded by the VOA.

If this is your first project in Hayes, these are worth a look: structural alterations in Hayes, flat conversions across Hillingdon, builders in London who take on conversions, renovations across London, how we handle flat conversions across London and Central Heating Installation Cost.

The GS Renovation Difference in Hayes

A conversion only works if the consented layout, the fire separation and the acoustic floors are built exactly as drawn, because the separating floors are sound tested and building control inspects the result. We work from your designer's approved drawings, sequence the separating floors and walls before the fit-out of each flat, and coordinate the registered electrician and gas engineer for the separate supplies. You get a written quotation after a site visit and one point of contact to completion.

• Free, no-obligation quotations
• Each flat's new electrics signed off by a registered electrician for Part P
• Separating floors built to the acoustic detail the sound test checks

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.