Side extensions transform layouts on the typical Greenwich semi-detached property — gaining a wider kitchen and a useful utility/WC off the back. RCB Design & Build delivers side extension projects right across Greenwich (SE10) from our Dartford base — typically on site within 48 hours of enquiry, with a fixed written quotation in 5 working days. Our typical side extension project in Greenwich costs between £33,000 and £88,000 in 2026, with most riverside apartments and Georgian and Victorian terraces landing around £60,500. We are FMB, TrustMark, Checkatrade and TrustATrader accredited and operate as a Principal Contractor under CDM 2015.
High-value heritage refurbs around Greenwich Park. Loft conversions and side returns popular in Charlton and Eltham. Working out of Royal Borough of Greenwich's area, we know the planners, the local building inspectors, and the named conservation officers — that personal relationship cuts weeks off the consenting timeline. Our typical Greenwich project is on riverside apartments within easy reach of Royal Observatory or Greenwich Park, and we work with a small panel of trusted London-area subcontractors we have used for years.
What's included in our side extension price
Foundations, single-storey side build-up to match existing brickwork and roof pitch, steel beam to remove load-bearing wall, glazing, first-fix M&E, plaster, screed. We coordinate party wall surveyor and structural calcs. Our written quotation covers labour, first-fix materials, project management, scaffolding, skips, Building Control fees and statutory inspections. Second-fix materials (kitchens, bathrooms, flooring, tiles, paint, sanitaryware) are supplied by the client as a deliberate cost-control measure — this typically saves homeowners £4,840–£9,075 in trade markup. We exclude planning fees, party-wall surveyor fees and structural engineer drawings, which we coordinate at cost.
Greenwich planning, party walls and Building Regs
Greenwich World Heritage Site buffer requires LBC for many alterations — schedule planning at the start. Side extensions in conservation areas must match prevailing roof slope, ridge height and bay-window pattern. Local material match is non-negotiable. Note that Greenwich has multiple conservation areas — design must match prevailing materials, roof shape and fenestration. Party Wall Awards are typically needed for any excavation within 3 metres of a shared wall — we coordinate the surveyor and serve notices. Building Control is lodged at the start, with inspections at foundation, damp-course, pre-plaster and completion stages.
Timeline and process for Greenwich projects
Side extensions run 6–10 weeks on site. Matching brick and roof pitch is the design challenge — we'll spend time sourcing the right brick before mobilisation. We hold a weekly call with the client throughout, send a written progress report with photos every Friday, and the lead PM is always reachable on WhatsApp. From SE10 postcodes we can have someone on site within 48 hours of a phone call.
Guarantees and after-care
Every project we deliver in Greenwich is backed by a 12-month workmanship guarantee. Where we install manufacturer-warranted systems (roofing membranes, windows, MVHR), the manufacturer warranty (typically 10–25 years) runs alongside. As an FMB member we can also arrange an FMB-backed 2-year insurance warranty on qualifying Greenwich schemes — worth considering for any project above £50,000.
Side Extension cost in Greenwich — 2026 price guide
Project size
From
To
Narrow side (≤10 m²)
£33,000
£43,000
Standard side (10–20 m²)
£40,000
£53,000
Wide side (20–30 m²)
£46,000
£63,000
Full side (30 m²+)
£53,000
£73,000
Indicative Greenwich (SE10) ranges for 2026. A site visit firms the figure to +/-5%.
Frequently asked questions
How much does a side extension cost in Greenwich in 2026?
Typical Greenwich pricing ranges from £33,000 to £88,000 depending on size, finish and site complexity. Greenwich sits in the mid-band of our delivery area. A free site visit firms the number up to ±5%.
How long will a side extension take in Greenwich?
Allow 6–12 weeks of design, planning and procurement before work starts, then a project-dependent build phase. Side extensions run 6–10 weeks on site. Matching brick and roof pitch is the design challenge — we'll spend time sourcing the right brick before mobilisation. We share a Gantt-style schedule with every quotation.
Will a side extension in Greenwich need a party wall award?
Almost always — excavating within 3 m of a shared wall triggers the Party Wall Act. We coordinate the surveyor and serve notices on the neighbours as part of the package.
Which areas of Greenwich do you cover?
We cover all of SE10 and the surrounding London postcodes from our Dartford base. Recent projects sit close to Royal Observatory and Greenwich Park. Anywhere within 45 minutes of Dartford is comfortably inside our core delivery zone.
Is RCB insured?
Yes — we hold £5 million Public Liability, £10 million Employer's Liability, full Contract Works insurance and Professional Indemnity. Certificates are provided with every quotation.
How do I get a quote?
Use the free instant calculator at /quote for a 60-second ballpark, configure your project in detail at /configure, or call +44 7359 872594. We respond to every enquiry within 4 working hours.