A successful rear extension on a larger Dulwich house starts with the existing rear building line and the depth of garden behind it. The period semi-detached family houses and the villas around Dulwich Park often have generous plots, which can tempt an ambitious footprint, but the useful question is how far the addition can project before it erodes garden amenity, overshadows the attached 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, then set a projection that is both liveable and defensible to a Southwark case officer. On a corner or wider plot the building line may also step, so the extension has to resolve where the original back wall changes plane rather than simply running straight across, and we draw that junction before committing to a footprint that a neighbour could reasonably contest.
The choice between single 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 detached and semi-detached villas — brings first-floor windows, outlook and a 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 boundary. We advise early which storey height a given house and plot can carry, because committing a two-storey scheme to a submission that the plot cannot support wastes a planning cycle. A common middle route is a full-width single storey with the first floor left untouched, or a two-storey element held well in from the flank so the upper part reads as a modest addition rather than a second full elevation over the boundary.
Keeping the extension subordinate to the host is what usually secures support in a conservation setting. On a Victorian or Edwardian villa the rear elevation has its own rhythm of openings, eaves and materials, and an addition that sits below the eaves, steps in from the flanks and picks up the brick or render of the original reads as part of the house rather than a bolt-on. Where the house sits within the Dulwich Estate's scheme of management, that subordination matters twice over, because the Estate's consent weighs the effect on the property and its setting alongside Southwark's own assessment. Subordination is not only a matter of height — it is also how the new parapet or eaves meets the original, how the return walls are set back, and whether the roof of the extension is legibly a later, lesser addition. We resolve those junctions in detail so the addition never competes with the elevation it grows from.
Mature trees and garden boundaries are frequently the deciding constraint on the larger Dulwich plots, and they are a house-extension issue as much as a landscaping one. A substantial tree in or near the garden can carry a protection order or sit within a conservation area, and its root protection area can dictate where foundations may go and how they are formed — often a piled or otherwise engineered solution rather than a standard strip footing. We establish the trees, boundary walls and any rights running along them at survey, because they can move the achievable rear building line as decisively as any planning policy. Boundary walls themselves matter too: an old garden wall may be a party structure, may be founded shallowly, and may not tolerate a new extension built hard against it, so the relationship between the addition and the existing boundary is designed rather than assumed.
Daylight and right to light deserve early attention because even the generously spaced Dulwich houses sit close enough for a rear extension to affect a neighbour. Southwark assesses daylight and sunlight to neighbouring windows using the established BRE tests, and a well-judged section — controlling height near the boundary and stepping the roof down — often keeps a scheme within them. Right to light is a separate civil matter that a planning consent does not resolve, so where an extension approaches a neighbour's window we flag it early so it can be addressed rather than discovered once the design is committed. The 45-degree relationship to a neighbour's nearest window is a useful early check on a rear projection, and where a scheme approaches it we test the section formally rather than trusting a rule of thumb, because a projection that reads generously on plan can fail on daylight once the height and boundary distance are drawn together.
From there the route is a coordinated one. We survey the house, test the extension against the planning, tree and daylight constraints, and develop a design a Southwark case officer can support, then produce the planning drawings and, once the principle is settled, the building-regulations package for construction. Where the property sits within the Dulwich Estate we run the scheme-of-management consent in parallel, and on the closely built semi-detached plots the Party Wall etc. Act 1996 usually applies, so we identify the notifiable neighbours early. The building-regulations stage then carries the real detail — the foundation type agreed with the structural engineer and any arboricultural constraint, the thermal upgrade to the new envelope, drainage runs and how they connect to the existing system, and the structural openings knocked through the original rear wall. The result is a rear extension that adds real space without unbalancing the house or its garden setting.
