Chelsea's tightly packed period houses leave one direction to grow — down. TrustBuilt Projects designs and builds basement conversions across SW3 and SW10, from underpinning and lightwells to BS 8102 waterproofing, all within the Royal Borough's strict basement policy.
Chelsea's Georgian and Victorian terraces — from the streets off the King's Road to the riverside and World's End end of SW10 — sit on small, valuable plots where extending outward is rarely an option. A basement adds a whole new storey for a cinema, gym, wine room or extra bedrooms, but because almost all of Chelsea falls within the Royal Borough of Kensington and Chelsea, the same demanding rules apply as the rest of the borough.
Under Policy CL7 and the 2016 Basements SPD, a basement here is generally limited to a single storey (double basements are refused in most cases), can cover no more than 50% of the garden, and must keep at least one 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 terraced streets the construction logistics are scrutinised closely.
A large share of SW3 and SW10 is listed or in a conservation area, so basements affecting a listed building face heavy restriction and need listed building consent. We start with the structural engineer's design, ground-water and basement impact assessment and 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, 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 garden basements at 50% of the garden, and requires at least a metre of permeable soil above any garden basement. We check your specific SW3 or SW10 site against the policy before designing.
Chelsea sits within the Royal Borough of Kensington and Chelsea, which adopted one of the country's strictest basement policies after a wave of large excavations. The rules protect neighbours, gardens, drainage and the conservation character — so getting the planning and construction-management documents right is essential, which is exactly where we lead.
It's much more restricted. Basements under or affecting listed buildings need listed building consent and are often refused, so we give an honest view early. Where a scheme is feasible we prepare the heritage and structural case to give it the best chance.
A single-room basement under the existing footprint is typically 20–32 weeks; a full-footprint basement with a lightwell runs closer to a year, and a basement under house and garden longer still. The party wall and excavation sequence drive the programme, which we set out in the written quote.
Free site visit, no obligation, written quote.
Book Your Free Visit →