It was a wave of large Chelsea excavations that prompted the Royal Borough's basement clampdown — so on SW3 and SW10 plots the planning case matters as much as the dig. TrustBuilt Projects designs and builds basement conversions across Chelsea, from sequential underpinning and lightwells to twin BS 8102 waterproofing, all within RBKC's Policy CL7 and the 2016 Basements SPD.
Chelsea's Georgian and Victorian terraces — from the streets off the King's Road to the artisan cottages of World's End and the riverside houses near Cheyne Walk — sit on small, valuable plots where extending outward is rarely an option, so a single excavated storey adds the cinema, gym, wine room or extra bedrooms owners want. It was the run of oversized 'iceberg' basements in Chelsea that pushed the Royal Borough to adopt one of the country's strictest basement regimes, so getting the planning right is the heart of the job.
Policy CL7 and the 2016 Basements SPD limit a basement here to a single storey (double basements are refused in almost all cases), to no more than 50% of the garden, and require at least a metre of permeable soil above any garden basement for planting and drainage. A Subterranean Construction Method Statement, Construction Traffic Management Plan and the Code of Construction Practice are all required — and on Chelsea's narrow streets off the King's Road, where there is nowhere to stand a lorry, the construction logistics are scrutinised especially closely.
The riverside streets near Cheyne Walk and the Embankment add a further factor: proximity to the Thames means groundwater and flood-risk have to be designed for, not assumed. A large share of SW3 and SW10 is also listed or in a conservation area, so we lead with the structural engineer's design, the ground-water and basement impact assessment and the party-wall awards, then underpin in sequence and tank to BS 8102 with a cavity-drain backup so the finished space stays dry for good.
Basement work is the most specialised we do, and prime Chelsea costs reflect depth, riverside ground conditions, listed status, lightwells and waterproofing. As a guide:
| Project type | Typical cost | Timeline |
|---|---|---|
| Single-room basement (under existing footprint) | £170,000 – £340,000 | 20–32 weeks |
| Full-footprint basement + lightwell | £340,000 – £620,000 | 32–52 weeks |
| Basement under house & garden | £580,000 – £950,000+ | 12–18 months |
| Listed / complex deep basement | POA | 12–24 months |
Every project is quoted in writing after a free site visit — these ranges are a guide only.
Usually yes, within RBKC's strict limits. Policy CL7 generally permits a single storey below ground, caps a garden basement at 50% of the garden, and requires a metre of permeable soil kept above it. We check your specific SW3 or SW10 site against the policy before designing.
Because the wave of very large excavations that prompted the Royal Borough to adopt its strict basement policy was concentrated here. The rules now protect neighbours, gardens, drainage and the conservation character, so the planning and construction-management documents carry real weight — which is exactly where we lead.
Yes. On the riverside streets close to the Thames, groundwater is higher and flood-risk has to be assessed, so the ground-water and basement impact assessment drives the waterproofing and drainage strategy. We design twin protection to BS 8102 — Type A tanking plus a Type C cavity drain to a sump with dual pumps and battery backup — so there are two independent lines of defence.
It's planned in detail, because there is often nowhere to stand a lorry off the King's Road or in World's End. Excavation muck-away, deliveries and the underpinning sequence all go into the Construction Traffic Management Plan and the programme, so the dig runs without blocking neighbours or the street.
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