House
extensions
in St John's Wood, NW8

The audit says side extensions have been especially harmful where open gaps between buildings have been blocked and glimpses of the gardens behind lost.

We therefore start with the back and the basement level, where space can usually be found without closing the gap, and treat a side extension as the exception.

Source: Westminster City Council: St John's Wood Conservation Area Audit SPD

The audit notes the earlier Italianate villas were usually fully stucco rendered with simple classical detail, and that yellow stock brick and stucco give most of the conservation area its coherence.

A rear extension in stock brick or painted render, with timber or slim metal glazing, usually sits more quietly beside these houses than a contrasting material.

Source: Westminster City Council: St John's Wood Conservation Area Audit SPD

The commonest brief for a St John's Wood extension is a kitchen that opens to the garden, with a table and a sitting area in the same room. Others want a garden-facing study, or a ground-floor bedroom and shower room for a relative who finds the stairs difficult.

We plan the room around how it will be used through the day: where the morning sun falls, where the table goes, and which doors stand open in summer. That decides the depth, the roof form and the glazing more than any rule of thumb.

Underfloor heating, a ventilated larder and storage built along the party wall are designed with the structure, so none of them has to be squeezed in later.

The 2004 mini guide counts some 470 listed buildings in the St John's Wood Conservation Area.

City Plan Policy 44 says works to listed buildings should preserve their special interest, protecting and, where appropriate, restoring original or significant fabric.

Westminster has 56 conservation areas covering 78% of the city, so most extension proposals here are judged as heritage proposals.

Sources: Westminster City Council: St John's Wood conservation area mini guide, Westminster City Plan 2019-2040 (2026, adopted January 2026)

Most extensions need building regulations approval, the Planning Portal says.

Where the extension opens into the house, the wall above the new opening needs supporting, usually on one or two beams.

Some clay soils swell and shrink with moisture, so foundations may need to be deeper, especially near trees.

Approved Document H's building-over-sewers rules apply to work over or within 3 metres of a drain or sewer.

In these large gardens we also check the root protection areas of mature trees before fixing the footprint.

Sources: Planning Portal: Is building regulations approval needed for an extension?, Planning Portal: Extensions, Building Regulations: Structural Opening, Planning Portal: Extensions, Building Regulations: Foundations, GOV.UK: Approved Document H, Drainage and waste disposal (2015 edition)

We begin with a measured survey of the house and garden, then sketch two or three ways of extending, with the planning risk of each set out plainly. Once you choose one, our architects prepare the application and our engineer designs the foundations and steelwork.

Party wall notices, the building control application and the Code of Construction Practice paperwork follow the planning decision. On site one project manager runs the work from the first excavation to the snagging list, and keeps the neighbours told what is coming.

The 12-month aftercare/defects period starts at handover.

Work covered by the Party Wall etc Act 1996 needs notice to the adjoining owners in the form the Act sets down.

Where owners cannot agree, one or more surveyors set down in writing what work is done and how, under the Act.

For a semi-detached villa, the party wall is usually the main structural question for a rear extension, so we serve notices once the engineer's design is ready.

Sources: GOV.UK: Party Wall etc. Act 1996 guidance, GOV.UK: Party walls and building work