A rear extension in Blackheath begins with the existing rear building line and the depth of garden behind it. The area's Victorian and Edwardian family terraces and period semi-detached houses often have generous gardens, which can tempt an ambitious footprint, but the useful question is how far the extension can project before it erodes garden amenity, overshadows a neighbour or reads as an over-development of the plot. We test single-storey depths in section against the daylight reaching neighbouring windows, the position of boundary walls and any mature trees, and set a projection that is both liveable and defensible when it reaches a case officer in Greenwich or Lewisham. Getting that depth right at the outset is what keeps a scheme moving, because a footprint fixed on optimism rather than evidence is the sort of thing an officer asks to be reduced, adding a revision cycle and weeks to the timetable before anything is built.
The choice between one and two storeys changes the assessment entirely. Single-storey rear extensions are the most common here and are judged largely on garden impact and neighbour daylight. A two-storey rear addition, realistic on some of the larger semi-detached houses, brings first-floor outlook, overlooking and the sense of enclosure over a neighbour's garden into play, and is far more sensitive on a semi-detached pair where the two houses share a flank boundary. We advise early which storey height a given house and plot can carry, because committing a two-storey design to a submission that the plot cannot support wastes months. Where a first-floor addition is viable, its rear windows are positioned and, if needed, obscured or set at high level so the overlooking objection that most often sinks two-storey schemes is designed out before the drawings are submitted rather than argued after a neighbour comments.
Garden levels are worth resolving early on any period plot. Where a garden falls away from the house or sits a step or two below the ground floor, a rear extension has to decide whether to hold the internal floor level and step down to the garden, or lower the new floor to meet it. That decision drives the foundation depth, the threshold detail and how the extension relates to the boundary walls on either side. On a terrace it also affects how the new roof lines up with the neighbours' back-additions, which the conservation assessment will look at along the rear building line. A change in level of only a step or two can decide whether the extension needs a shallow ramp or a run of internal stairs to the garden, so we settle it at the survey rather than discovering it once the slab is being set out.
Trees, roots and drainage govern what the foundations have to do. Blackheath's generous gardens often carry mature trees, and where they are near the extension the foundations may need to be deepened or engineered to a specialist design so that seasonal ground movement does not later crack the structure. The existing drainage — the soil and rainwater runs that cross the back of a period house — usually has to be diverted or built over under a build-over agreement with the water authority. We identify the trees, the likely root protection and the drainage runs at survey, because each of them can reshape the foundation design and the cost before a line is drawn on the extension itself. Trees within a conservation area can also carry protection in their own right, so we check their status early — a foundation solution that works around a protected tree is usually cheaper and quicker than a scheme that assumes it can be removed.
Party walls are almost unavoidable on a terrace or a semi-detached house. A rear extension typically bears new structure onto, or excavates alongside, the shared boundary walls, which engages the Party Wall etc. Act 1996 with the neighbours on one or both sides. Notices are served before work starts and are separate from the planning decision, so we identify the notifiable neighbours early and coordinate with a party wall surveyor so the award does not stall a build that already has consent. On a full-width rear extension across a terrace, both flank walls are usually in play, and the neighbour relationship is best opened with a design that visibly respects their light and outlook. The award can also permit access onto a neighbour's land to build the flank wall, which is worth settling before the programme is fixed, since a dispute at that stage can hold up a build for weeks even where planning permission is already in place.
From there the route is a coordinated one. We survey the house, confirm whether Greenwich or Lewisham applies and whether the property is listed, then test the extension against the conservation, daylight and neighbour constraints before developing a design a case officer can support. We prepare the planning drawings and supporting material, and once the principle is settled, the building regulations package that covers structure, foundations near trees, drainage, insulation and the new rear elevation for construction. The aim is a rear extension that adds genuine, usable space and opens the house to its garden without unbalancing the original building or its setting within the conservation area. Sequencing the work this way — authority and listing first, constraints tested next, then planning and only afterwards the technical package — keeps the client from paying for detailed drawings against a footprint that later has to change, and gives the builder a coordinated set of information to price and construct from.
