Hampstead's hillside houses and high water table make basements a specialist job. TrustBuilt Projects designs and builds basement conversions across NW3 — underpinning, lightwells and twin BS 8102 waterproofing — working within Camden's Policy A5 and its basement impact assessment from the outset.
Hampstead's Victorian and Georgian houses sit on a steep, tightly protected hill where extending outward is rarely possible, so a basement is how owners win a gym, cinema, utility or extra bedrooms. But NW3 is in the London Borough of Camden, whose Policy A5 is strict — and the area's geology, with springs and underground streams running off the Hampstead hill, makes the ground-water question more serious here than almost anywhere in London.
Camden's Policy A5 limits a basement to a single storey, allows it under no more than 50% of the garden and to extend no more than 50% of the garden's depth, and requires the unaffected garden to remain a single continuous area. Crucially, every application must include a Basement Impact Assessment prepared by a chartered engineer — with the hydrology and flood-risk elements signed off by a hydrologist or flood-risk specialist — to prove the dig won't alter groundwater flow or harm neighbours.
Much of Hampstead Village is listed and within a strict conservation area, and the narrow, steep lanes make access and muck-away a genuine planning factor. We lead with the structural engineer's design, the Basement Impact Assessment and party wall awards, protect trees and root systems as the policy requires, then underpin sequentially and tank to BS 8102 with a cavity-drain backup so the basement stays permanently dry.
Basements are the most specialised work we do, and in Hampstead the ground-water conditions, access and assessments all feed the cost. As a guide:
| Project type | Typical cost | Timeline |
|---|---|---|
| Single-room basement (under existing footprint) | £160,000 – £320,000 | 20–32 weeks |
| Full-footprint basement + lightwell | £320,000 – £580,000 | 32–52 weeks |
| Basement under house & garden | £520,000 – £900,000+ | 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.
Yes. Camden's Policy A5 requires a Basement Impact Assessment by a chartered engineer for basement applications, with the hydrology and flood-risk parts signed off by a suitable specialist. Given Hampstead's springs and underground streams this is taken very seriously, and we coordinate it as a first step.
Policy A5 generally limits a basement to a single storey, under no more than 50% of the garden and extending no more than 50% of the garden's depth, with the remaining garden kept as one continuous area. We design within those limits so the scheme is supportable.
It can be — the hill has springs and underground watercourses, which is exactly why Camden demands the hydrological assessment. We design twin waterproofing to BS 8102, Type A tanking plus a Type C cavity drain to a sump with dual pumps and battery backup, so groundwater is managed and the space stays dry.
Yes — it's a key part of the plan here. Excavation muck-away, deliveries and the construction sequence all need careful management on the Village's steep, narrow streets, and we set the logistics out in the programme and the quote so the build runs without conflict.
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