What 'new build' actually means in London — and the three viable routes
Building a new house in London is a long, complex undertaking, and most prospective clients aren't fully clear on which of the three viable routes they're on until we have an initial conversation. Route one: infill plot. An empty piece of land in an existing residential area — typically the side garden of an existing house, a corner plot, a former garage site. Planning is the main risk: a refused infill is dead money. Route two: knock-down rebuild. Demolish an existing building (sometimes for sound reasons — failed structure, total energy non-compliance, total layout obsolescence) and build new on the same footprint. Easier planning than infill (the building line is established), expensive demolition and groundworks. Route three: large extension that effectively becomes a new house (re-cladding, re-roofing, total internal reconfiguration). Often cheaper, easier planning, but constrained by the existing geometry. We assess all three for any prospective new-build client.
Planning new builds: the make-or-break phase
Planning permission for a new build in London is the single biggest commercial risk in the whole project. Typical pre-app to decision: 18–32 weeks. Refusal rate on London infill plots: 35–45% first time, often improving on appeal but adding 6–12 months. Knock-down rebuilds are easier but conservation areas, Article 4 zones, the London View Management Framework and the London Plan all impose constraints that catch unwary architects. We don't take on new-build clients without first running a free planning desktop assessment of the site — three days, free, includes a heritage check, conservation context, local plan policy review and a preliminary comment from the planning authority where useful. Where we do progress, our planning consultant works site-by-site with the local case officer, and we maintain a 78% first-submission approval rate (industry average 55–65%) by not submitting marginal applications.
Groundworks: 12 weeks of foundations before anything visible happens
Most homeowners under-estimate the groundworks phase of a new build. Demolition (week 1–3), site setup and welfare facilities, asbestos survey and removal if required, ground investigation (boreholes and trial pits to determine bearing capacity), foundation design, foundation dig and pour. London geology is variable: most of central and east London is on London Clay (cohesive, foundations need to be 1.5–2.5m deep depending on proximity to trees), west and south-west London has more granular deposits, the Thames terrace gravels are excellent (shallow foundations possible), made ground and old fill creates difficulty everywhere. Foundation specification varies wildly: traditional strip on solid clay £15,000–£30,000 for a typical 4-bed plot; piled raft on poor ground £45,000–£90,000; underpinning of adjacent properties (for tight infill plots) £25,000–£60,000. Groundworks are 8–12 weeks of programme and 12–18% of total project cost.
Superstructure: timber frame, SIP panel, masonry — which to choose
Three structural systems for London new builds. Traditional masonry (block-and-block cavity walls with brick or render outer skin) — proven, easy to source, every trade knows it, slowest to weatherproof (12–16 weeks shell). Timber frame (pre-fabricated panels craned on site) — faster to weatherproof (4–8 weeks), better thermal performance, slightly higher cost than masonry. SIP (structural insulated panels — OSB skins around foam core, factory-built) — fastest to weatherproof (3–5 weeks), best thermal performance and airtightness, premium-spec choice for Passive House builds, highest material cost but fastest programme. We've built all three and recommend based on planning constraints (planners sometimes prefer one system for heritage compatibility), site logistics (timber frame and SIP need crane access), client priorities (programme versus capital cost), and energy targets. Our standard mid-spec new build is timber frame; high-spec Passive House is SIP.
MEP: services design that determines running cost for 30 years
Mechanical, electrical and plumbing services design is what separates a generic 2024 new build from a forward-looking one. Heating: heat pumps (air source or ground source) are the current default for any new build under current building regs; we specify Daikin, Mitsubishi or Vaillant Arotherm depending on demand and plot. Cooling: increasingly specified for London new builds, either as air-to-air heat pump dual-function or as small VRV split system in bedrooms. Hot water: unvented megaflow at 200–300L with heat pump or direct electric immersion. Ventilation: MVHR is now mandatory for any airtight new build (under 5 m³/h.m²) and we install with full ductwork co-ordination during structural phase. Electrics: full 18th Edition consumer unit with RCBO, smart metering, EV charging point (one to two per dwelling), solar PV ready (battery storage commonly retrofitted), Cat6 to every room, structured cabling cabinet, full lighting design with dimmable scene control. The combined MEP package on a £1.5M new build typically £180,000–£250,000.
Building control, warranty, NHBC: the certification chain that delivers a saleable house
A new build is not finished until it has full certification. Building regulations sign-off (via local authority or approved inspector) — 8–12 inspections through the build, final certificate at completion. Structural warranty: 10-year NHBC, LABC or Premier Guarantee — we use NHBC as standard, premium for properties intended for sale within 10 years; LABC for owner-occupier where premium matters. Energy Performance Certificate — required for sale or rent, we design to Band A or B (90+ SAP rating) as standard, with Passive House standard available as upgrade. Sound testing — required at completion for any property in a planning constraint area or above ground floor flat. Air-pressure testing — required to demonstrate compliance with the 5 m³/h.m² limit under current Part L; we routinely test at 1.0–2.5 m³/h.m² on our standard new builds, demonstrating significantly above-compliance airtightness. Full certification pack supplied to client at handover.
Programme, cost and the reality of a 12-month build
A typical 200m² family home in London on an infill or rebuild plot, mid-spec, runs 40–48 weeks from site mobilisation to handover (after planning, which is the prior 18–32 weeks). Cost on the same property typically £700,000–£1,200,000 building cost (3,500–6,000 per m²) plus £80,000–£200,000 in fees, plus VAT (new builds are usually zero-rated, recoverable if client is registered or qualifies under DIY Builder scheme). The largest cost component is fit-out — kitchens, bathrooms, joinery, flooring — typically 25–35% of total. Structure and shell typically 30–40%. MEP 18–25%. Fees and management 8–12%. Client decisions during fit-out phase (typically months 7–11) determine 80% of the cost variance between a £700k and £1.2M home of the same size. We model this transparently at design phase so the client makes informed trade-offs rather than discovering them at variation-order stage. Full Gantt, full cost model, full decision schedule — published at contract sign and updated weekly.
