Basement impact assessments in Southwark

Terraces, flats and heritage in the borough

Southwark's published record lists 53 conservation areas, 919 listed entries and 480 Article 4 directions. A basement under a listed house, or inside a conservation area, carries the heritage case in the same submission, so the lightwell, the front elevation and any railings are drawn and justified together with the engineer's findings.

Only 21.8 per cent of households live in a house, so most of the borough is flats and maisonettes. Where a basement is realistic it is usually a lower-ground conversion beneath a terrace, and an average terraced home sells for £838,160. That price is why owners weigh a dig against moving.

Domestic gardens cover just 17.6 per cent of the borough's land in the national land-use database. Rear plots are short, so neighbours' foundations are never far from the excavation, and the party wall and underpinning questions arrive early.

What Southwark's decision figures tell a basement client

In its latest year the council decided 558 householder applications, granted 94.8 per cent and decided 95.3 per cent inside the statutory period or an agreed extension. Minor applications, which take in small residential schemes, were granted at 90.2 per cent across 560 decisions.

These are borough-wide rates, not a forecast for your street. They do show a council that decides quickly and checks detail, so a pack in which the report, sections and flood evidence agree with each other is worth more than a thick one. If the basement is part of a larger job, our planning drawings in Southwark are produced to the same pack.

Neighbours, drainage and the dig itself

A party wall notice is needed for excavation within 3 metres of a neighbouring building that goes below its foundations, and within 6 metres where the dig meets a diagonal plane drawn down from those foundations. Serve it at least 1 month before work starts, with plans and sections.

Building Regulations then govern the floor and walls. Where groundwater can rise within 0.25 metres of the lowest floor, it must be drained or otherwise controlled. Our structural calculations in Southwark page explains how the engineer's design and our drawings are issued together.

Lightwells, railings and the street frontage

Front elevations are where a Southwark basement is seen. Terraces in a conservation area usually have shallow front gardens, so a lightwell has to be drawn against the street with its railings, grille and any change to the bay window. Officers compare it with the houses either side, and a design that echoes an existing lightwell is easier to explain than a new type. We draw the front elevation in context, with the neighbours shown, so the precedent is visible without a search.

Rear lightwells and a glazed link to the garden are judged on amenity: the daylight they send into a neighbour's room, and the noise from any plant room. That is the amenity limb of the design policy, and it belongs in the same pack as the water evidence.

Cost, timing and where to begin

There is no list price, because depth, soil and flood layers change the work. After the free check you receive a fixed quote, and if the council is unlikely to ask for a full report on your project we say that plainly.

For the wider picture, read our overview of architectural drawings in Southwark. Neighbouring boroughs apply the rule differently: see Lambeth and Lewisham, or the national guide at basement impact assessments.