Full architectural technology service for basement digs and cellar conversions in Lewisham — structural underpinning design, waterproofing strategy, Party Wall coordination, planning where required, and building regulations through to completion certificate.
Full architectural technology service for basement digs and cellar conversions in Lewisham — structural underpinning design, waterproofing strategy, Party Wall coordination, planning where required, and building regulations through to completion certificate.
Housing stock in Lewisham: Victorian and Edwardian terraces across Brockley, Honor Oak, Forest Hill; 1930s semi-detached in Catford and Hither Green; post-war mixed in Deptford.
Character: Generally permissive planning compared to central boroughs; loft conversions and side-return extensions routinely approved under PD.
Desktop study plus measured survey assessing existing foundations, ground conditions, water table level and underpinning viability for your Lewisham property.
New-build basements and lightwell extensions need planning permission. Cellar conversions of existing space are usually Permitted Development. We confirm the route and submit where needed.
Underpinning sequence drawings, reinforced concrete design, temporary works strategy — all to Eurocode with chartered engineer sign-off.
BS 8102:2022 compliant — cavity drain, cementitious tanking or membrane system specified for Lewisham's ground conditions and water table.
Full Plans application to Lewisham Council Building Control or an approved inspector covering structure (Part A), fire safety (Part B), damp-proofing (Part C), ventilation (Part F) and thermal performance (Part L).
Almost every Lewisham basement triggers Party Wall notices. We also manage Thames Water Build Over Agreements where within 3m of a public sewer.
Single planning or regs submission.
Planning + building regs + structural.
Listed, conservation, complex sites.
Direct answers to the questions Lewisham homeowners ask every week about basement conversion drawings.
Start a free quote →Converting an existing cellar to habitable space in Lewisham usually does not require planning permission — it is an internal alteration. However, excavating a new basement, adding lightwells, or lowering floor levels to create a new storey typically does require planning. Lewisham does not have a borough-specific basement policy beyond the national framework — basement conversions are generally permissible subject to structural, drainage and flood-risk considerations. Thames Water Build Over Agreements apply where you're within 3m of a public sewer.
Our fixed-fee architectural package for a Lewisham basement starts at £1,950 (planning + building regs + structural + waterproofing specification). Build costs in Lewisham range from £3,000–£5,000 per square metre — a typical 40m² basement is £120,000–£200,000 to construct. Costs are higher than extensions due to underpinning, waterproofing and temporary works.
Most properties in Lewisham can support a basement conversion, provided foundations are deep enough or can be underpinned, the water table is manageable, and there are no significant tree root or drainage constraints. Victorian and Edwardian houses in Lewisham often have existing cellars that can be deepened. We assess suitability at the initial survey.
BS 8102:2022 requires a waterproofing strategy appropriate to the site's water table and ground conditions. In Lewisham, this typically means a Type C cavity drain membrane system (most reliable), sometimes combined with Type A barrier protection. The strategy must be specified by a qualified waterproofing designer — included in our package.
A typical Lewisham basement conversion takes 6–12 months to build once drawings are approved. Our architectural package takes 5–8 weeks from instruction to Building Control submission. The longer build time reflects the sequential underpinning process, which must proceed in careful stages.
We cover every London borough with the same fixed-fee approach. If your property sits on a boundary, here are the neighbouring options.
We cover every architectural technology service in Lewisham with one chartered team.
From £840. A fixed-fee, end-to-end service — measured survey, scaled drawings, Design & Access Statement where required, Planning P...
From £840. A construction-ready drawing package compliant with every Approved Document — Part A structure, Part B fire, Part L ther...
From £1,225. Every loft type across every {location} roof line — dormer, mansard, hip-to-gable, L-shape, Velux. LDC or full planning ...
From £1,225. The whole spectrum — rear extensions, side returns, wraparounds, double-storey, basement digs. Planning-led design with ...
From £1,575. {location}'s most space-efficient loft solution when PD-route dormers are blocked. Our chartered team designs mansards t...
From £995. Turn your unused {location} garage into a bedroom, home office or open-plan kitchen-diner. Planning route assessment, fu...
From £350. Chartered structural engineer calculations for every residential intervention in {location} — steel beams, lintels, pad ...
From £450. End-to-end Party Wall Act 1996 service for {location} — Section 1, 3 and 6 notices, schedule of condition surveys, party...
From £1,225. London's most popular loft type — the full-width rear dormer. Planning or Permitted Development route assessed for your ...
Free quote in 60 seconds. Fixed fee from £1,950. MCIAT chartered.
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