House Extension in Finchley

Finchley Church End sits at the junction of Regents Park Road and Hendon Lane, and it is the oldest of the three Finchley centres. East Finchley and North Finchley both grew later, along the same road running north out of London. The housing at Church End changes character over a very short distance, which is the single most useful thing to know before planning any work here. Along Gravel Hill, College Terrace and the side streets off Hendon Lane stand modest two-storey Victorian cottages in brick or render, roofed in Welsh slate at a shallow pitch, with single-storey canted bays, recessed doorways and white-painted timber sashes. Behind the Edwardian shopping parades on Hendon Lane and Regents Park Road, with their prominent chimneys and elaborate array of gables, sit flats and maisonettes on tight plots. Further east on East End Road, the Avenue House Estate holds a group of Italianate villas built in the 1850s in stucco and slate, three and four storeys high. Beyond the conservation boundary the stock changes again, to the wide-fronted inter-war semis that most people picture when they think of Finchley.

That range decides what can be built and what it costs. Take a Victorian cottage on one of the terraces off Hendon Lane. It has a narrow plot, a shallow-pitched slate roof, and solid brick walls with no cavity. A side return is usually the only route outwards. An inter-war semi three streets away is a different house. Cavity wall, hipped roof, wide side plot. That opens up wraparound and double-storey options the cottage cannot take. Underneath all of it is heavy, poorly drained London clay. Foundation depth and trench fill quantities are usually the first thing that moves a price in this postcode.

Then there is the conservation area, which most Church End owners misunderstand in both directions at once. Designation on its own removes more than people expect. Side extensions, anything above a single storey, roof alterations and exterior cladding all fall outside permitted development the moment a house sits inside the boundary. What survives is the single-storey rear extension, which happens to be what most owners here actually want. Finchley Church End was designated in July 1979 and is one of sixteen conservation areas in Barnet, ten of which are covered by or subject to an Article 4 Direction. The council’s own character appraisal sets out what the direction adds on top of that, and it lands on the front of the house rather than the back.

These are the small terraced and semi-detached cottages the character appraisal identifies as the characteristic housing type of the area. They are two storeys, brick or rendered over brick, with slate roofs of shallow pitch and neat canted bays at ground floor. Walls are solid brick rather than cavity, usually a single brick or brick-and-a-half thick. Insulation therefore has to be added internally or externally rather than injected. Any new opening needs a properly sized lintel and padstone. Damp proof courses in houses of this age are often slate, or absent altogether. A new floor slab at the rear has to be tanked and tied into whatever is there. Plots are narrow. Rear gardens are shorter than owners expect once the existing outrigger is measured.

The large mid-nineteenth-century villas around the Avenue House Estate are stucco over brick, with slate roofs and tall chimneys. Several are statutorily listed. That puts any alteration into listed building consent territory rather than ordinary planning. The modern flatted developments off Regents Park Road and Hendon Lane are a separate case again. Immediately outside the conservation boundary, and across the wider N3 area toward North Finchley and Whetstone, the stock is predominantly inter-war semi-detached with cavity walls and hipped roofs. Those are the houses where the widest range of extension types is genuinely available.

The typical Victorian cottage plan puts a narrow kitchen in a rear outrigger. A separate reception sits in front of it, with a side passage alongside. Opening that up means removing at least one load-bearing wall, and usually the rear wall of the main house as well. The result is a single room running the full depth of the plot. That is what most people are buying when they ask for a kitchen extension. The constraint is width rather than depth. On a plot of this shape the gain comes from filling the side return, not from pushing further into the garden. Garden depth here is limited, and rear projection quickly darkens the middle of the house.

Church End cottages generally have an external soil stack and a shallow drainage run along the rear elevation. Both sit exactly where a new extension wants to go. Moving a stack internally is straightforward in principle and disruptive in practice, because it affects the bathroom above. Building over or near a public sewer needs agreement with the water authority before work starts, not after. Where a manhole falls inside the new footprint, it is rebuilt with a double-sealed cover and kept accessible. These details decide whether a build runs to programme.

Indicative range: a single-storey kitchen extension on a Church End terrace typically falls between £45,000 and £85,000 depending on plot width, glazing specification and how much structural work the existing house needs.

For an attached house, a single-storey rear extension is permitted development up to three metres of projection. For a detached house the figure is four metres, subject to height and boundary conditions. Larger projections can be pursued under the prior approval route. The council notifies the adjoining owners and determines the application on the basis of any objection received. Inside a conservation area those rights are already restricted, and the larger-home route is not available. On the Church End terraces the practical limit arrives before the planning limit. Garden depth runs out first.

A wraparound combines a rear projection with the side return infill in one structure. It produces the largest single gain available at ground floor. It suits the inter-war semis in the wider N3 area, where the side plot is wide enough to take it. It suits the Church End cottages far less, because the return is narrow and the garden shallow. On a semi, the roof form shapes the whole job. A flat roof with a lantern gives the cleanest junction with the existing house. A shallow mono-pitch reads better from the garden and costs less to make watertight.

Indicative range: side return from £40,000 to £70,000; wraparound from £65,000 to £110,000, depending on structure, glazing and ground conditions.

Most single-storey home extensions in N3 are finished with a warm-deck flat roof in EPDM or GRP. A lantern or rooflights bring light into the middle of the plan. The warm deck puts insulation above the deck rather than between the joists. That avoids the condensation problems older cold-roof construction produced. Brick or render is matched to the host wall where the extension is visible. Where it is not visible from any public vantage point, there is more freedom in the finish. Falls, outlets and the parapet detail determine whether a flat roof lasts.

Converting or replacing an attached garage is the least disruptive way of gaining a room on the inter-war stock. The structure and the foundation already exist. The work is rarely as simple as filling the opening. Garage slabs are usually laid without insulation and often without a damp proof membrane, so the floor is normally taken up and relaid. Existing walls are frequently single skin and need an inner leaf built, insulated and tied. Extending the garage forward, rather than simply converting it, puts the front elevation in play. Inside the conservation area, that is exactly where the Article 4 direction applies.

Indicative range: single storey from £40,000 to £75,000; double storey from £80,000 to £140,000; garage conversion from £18,000 to £32,000.

Nine classes of development are brought under planning control. Enlargement, improvement or other alteration of a dwelling house, including extensions and the replacement of windows and doors. Alterations to the roof slope, including rooflights. Painting the exterior. The erection, alteration or removal of a chimney. The provision of a hard surface. Installation of a satellite dish. The erection, improvement or alteration of a gate, fence, wall or other means of enclosure. The demolition of any of those. The erection of a porch.

The qualification runs through all of it. The direction applies only where that part of the proposed development fronts a highway or open space. In practice the front elevation, the front boundary treatment, the front roof slope and the front garden are controlled. A rear extension on a house not fronting an open space is assessed under the ordinary conservation area rules instead, not under the direction. The direction was also served on a defined set of properties, not on every house in the conservation area. Establishing which category an address falls into is the first step on any Church End project. It can be answered before a survey.

Where a scheme is genuinely permitted development, a lawful development certificate is worth obtaining. It is not compulsory. It settles the position with the council in writing, and it is the document a buyer’s solicitor asks for later. Where a scheme exceeds permitted development but qualifies for the larger home extension route, prior approval applies. The council notifies adjoining owners and determines the application on the basis of any objection received. Neither route survives an Article 4 direction that has removed the underlying right. A full householder application is then the only path.

Architectural drawings, structural calculations, the planning application, building control and the construction all sit with one firm on one contract. That removes the gap which opens when a designer hands drawings to a builder who then prices around them. Our office is in Finchley N3, on The Grove, a few minutes from Church End. A site visit does not involve a trip across London. The full process runs from a free survey and a fixed written price against a defined scope, through to handover.