Golders Green grew rapidly after the Northern line arrived in 1907, and the housing that followed is the reason an extension here behaves differently from one in a dense Victorian terrace. The stock is predominantly 1920s-30s semi-detached and detached houses, larger double-fronted villas and Edwardian bay-fronted houses, generously built, with good ceiling heights and mature gardens. That gives most houses something the inner-London terrace does not have: a flank. The space beside the house — a side gap between a semi-detached pair, a driveway, a garage, or on a detached house a genuine margin on both sides — is usually the cheapest square metres on the plot, because it can often be built on at ground level without eating the garden at all. The first design conversation we have in NW11 is therefore about the side of the house before it is about the back of it.
A flank extension is not a side-return infill, and treating it as one is the most common design error we are asked to correct. On a terrace, a side return is a narrow alley beside a rear closet wing, hemmed by party boundaries. On a Golders Green semi, the flank is a full-height side elevation that faces open ground and is visible from the street, and the gap it sits in is part of what gives the street its rhythm. That visibility is the whole planning argument. A single-storey flank extension that keeps its roof below the eaves, holds a set-back from the front building line and does not read as widening the house to its boundary is a very different proposition from one that fills the gap flush with the front elevation. The same footprint, drawn two ways, produces two different answers.
The two-storey side addition is the ambitious version of that move, and it is realistic on a good number of detached and semi-detached houses here. It is also where a design either respects the pair or ruins it. On a semi-detached house the two halves were drawn as one composition, and a first-floor side extension that comes forward to the main front wall and continues the ridge at full height turns a pair into a terrace and reads as a second house bolted on. Setting the side extension back from the front elevation, setting the ridge down below the main ridge, and continuing the original roof pitch and hip rather than inventing a new one is what keeps the addition subordinate. We test that in elevation with the attached neighbour drawn alongside, because on a semi the neighbour is part of your design whether you like it or not.
Garages and driveways are the quiet opportunity in this stock. Where an interwar house here has a side garage or a hardstanding that is now too narrow for a modern car, it is usually doing very little for the house. Absorbing it into the plan can widen the ground floor across its full depth and connect the front of the house to the rear, and it often does so without a single square metre lost from the garden. The technical work is unglamorous and decisive: the garage is rarely built to habitable standard, so it typically means new foundations or underpinning to match, a properly insulated and damp-proofed floor build-up, a rebuilt or lined flank wall and a roof that resolves into the existing. Whether it stays as a garage door opening or becomes a window changes the street elevation, which is where a conservation-area address will be tested.
Rear projections still matter, but on these plots depth is a judgement about the garden rather than a race to the boundary. The mature gardens are one of the reasons people buy in Golders Green, and an extension that swallows the useful part of one to gain a room that is dark at its centre is a poor trade. The constraints that actually decide the depth are the daylight and sunlight reaching neighbouring windows, assessed using the established BRE tests; the height of the extension close to a shared boundary, which a stepped or lowered roof near the party line often resolves; and the amount of original garden the national permitted development regime allows to be covered, where that route is live. Right to light is a separate civil matter that a planning consent does not resolve, and where a rear projection approaches a neighbour's window we flag it early rather than late.
Underneath the planning question sits the construction one, and on an extension it is mostly structure, drainage and fire. Opening a flank wall or removing the rear wall of a semi transfers load, so beams and their bearings have to be designed and their padstones detailed before the wall is touched. Building along or near a boundary brings the Party Wall etc. Act 1996 into play — building on the line of junction, or excavating for foundations within three or six metres of a neighbour's structure, requires notice, and it is separate from the planning decision. Where the rainwater or soil drainage runs down the side of the house — a layout the survey has to establish for the address rather than assume — it sits exactly where a flank extension wants to go, so runs are diverted or built over under agreement with the water authority. And a full-width rear extension can turn an existing room into an inner room, which the building regulations treat as an escape problem, alongside structure, insulation, ventilation and waterproofing.
Our route through it is sequenced to answer the expensive questions first. We survey the house and plot, establish with Barnet whether the address carries a conservation-area or Suburb constraint and what permitted-development allowance, if any, has already been spent, and only then decide whether the project is a lawful development certificate, a prior-approval notification or a full householder application. From there we develop the extension against the neighbour relationship, the roof and the street elevation, prepare the planning drawings, and once the principle is settled produce the building regulations package for construction, coordinating the structural engineer and party wall surveyor. We do not promise approval — no architect honestly can — but we can make sure the scheme submitted is the one the house and its plot can actually carry.
