Kitchen Extensions Forest Hill

A kitchen extension in Forest Hill is built onto the housing the area is known for, the Victorian terraces and villas of SE23, joining the kitchen, dining space and garden doors into one room. Where a garden falls away from the house, as some do on the hillier streets around the Horniman Gardens, levels, drainage and the height of the new boundary wall shape the design as much as the floor area does. We build the shell, fit the steel into the house and install the kitchen in one programme.

In Forest Hill, a rear kitchen extension of about 30 square metres typically costs £45,000 to £97,500 excluding VAT, or £60,000 to £100,000 for a side return (indicative London ranges, Resi, MyBuilder and Checkatrade, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Forest Hill: the structural engineer we appoint designs the foundations and steel, we build the room and fit the kitchen, and a registered electrician certifies the electrics.

How deep and how high a Forest Hill rear extension can go

Lewisham's own guidance sets the starting point for a planning application: its Alterations and Extensions SPD, adopted on 24 April 2019, says rear extensions should generally be no more than 3m deep on terraced or semi-detached properties. The same document says extensions up to 3m long should generally be no more than 3m high on the boundary. For you that means the designer works to those two numbers first and argues for more only where the plot and the neighbours' windows allow it. A build under permitted development is measured against the national limits instead.

The SPD adds a limit that bites on shorter plots: an extension should never take up more than half the depth of the original rear garden or yard. Garden depths vary from street to street in Forest Hill, and a yard tucked behind a closet wing can be short, so measure the garden before settling on a layout. We take the drawings the designer produces and set the programme around the footprint the consent allows.

Housing in Forest Hill

Take the 11,040 or so homes the valuation list gives Forest Hill: 58% flats, 42% houses, 54% from before 1919, 13% interwar and 30% post-war. Since most homes here are flats, only a ground floor flat in Forest Hill with its own garden can extend its kitchen.

Side returns on terraces, wider rear rooms on villas

The house type decides the shape. 28% of homes in Forest Hill are terraced houses and 14% are semi-detached or detached. On a terrace the gap beside the closet wing is the obvious space to fill, which turns a narrow galley into a kitchen the full width of the plot. The work then runs along a shared boundary, so the new wall, gutter and roof edge need careful detailing where they meet next door. A new wall on the boundary line, or steel bearing into the party wall, is notifiable under the Party Wall Act, and the building owner serves those notices.

A semi or detached villa has room, where the plot allows, to go straight back or to wrap round the corner of the rear wing. That tends to mean a longer steel over the old back wall and a bigger opening, which the structural engineer we appoint designs before anything is taken down. A flat is a different case: householder permitted development rules for extensions apply to houses only and not to flats and maisonettes, so a ground floor flat needs planning permission for any extension.

Drains under a Forest Hill extension and the build over question

Check the drains before you fix the footprint. Lewisham's building control guidance says you must apply for a build over agreement before doing any works if your home is within 3 metres of a public drain or 1 metre of a public lateral drain. That agreement is made with the sewerage company. Behind a Forest Hill terrace a shared run can cross the ground the kitchen will sit on, so a camera survey of the drains early in the design saves a redesign later.

Where Lewisham is your building control body, it uses a full plans application for any new proposal to build above or within 3 metres of a drain or sewer. The quicker building notice route, where work can commence within 48 hours, is then not available. On a full plans application its building control sends a decision within five weeks unless the applicant has given a three week extension. We plan the dig, the new manholes and the drains test around that approval, and the sink and dishwasher waste go in before the slab is poured.

Roof lights, glazing and the conservation area

Light is what makes a deep kitchen work. Where the new roof is flat or shallow, it takes flat glazing or upstand roof lights, set out so the light falls on the worktop run and the table rather than on the back of the units. Lewisham's SPD has a separate rule for the house itself: rooflights should ideally be flush and never project more than 150mm above the original roof slope, which matters if you also want light through the back addition roof. The glass area also has to satisfy Part L, so it is balanced against insulation in the energy calculations.

If the house sits in the Forest Hill conservation area, originally designated in 1976 and extended in 1994 and in 2010, the rules tighten. Under national permitted development rules, all side extensions on designated land such as a conservation area require householder planning permission, and that catches a side return infill. Lewisham requires a heritage statement for all planning applications affecting buildings in conservation areas, so allow time for that document and the decision before a start date is fixed with us.

• Hob gas supply altered by a Gas Safe registered engineer
• Wet underfloor heating laid in the new screed
• Foundations, drainage and slab with the kitchen services cast in

VOA Council Tax stock of properties, March 2025, for Forest Hill West, Forest Hill East and Honor Oak. Counts rounded by the VOA.

Once you know the scope of the kitchen extensions in Forest Hill, it helps to read kitchen renovation in Forest Hill, kitchen extensions across Lewisham, fitting the kitchen itself, how building control inspects an extension, how we handle kitchen extensions across London and Renovating a 1930s Semi.

Why Choose GS Renovation in Forest Hill

We run the whole job, from setting out and the dig through the steel, roof and glazing to the kitchen itself, with our own trades rather than a subcontractor chain and one named point of contact for you. The steel is designed by the structural engineer we appoint, and we build to the consent and the engineer's details. You get a written quotation after a survey, the programme in advance, and a plan for keeping the house usable while the back wall is open.

• Cooker extract taken outside through the new roof or flank wall, not recirculated
• Screed left to dry before the kitchen floor finish goes down
• 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.