Garage Conversion in Lewisham | RCB Design & Build
Garage conversions are the most cost-effective way to add a habitable room in Lewisham — typically gaining a 15–20 m² home office, gym or guest bedroom. RCB Design & Build delivers garage conversion projects right across Lewisham (SE13) from our Dartford base — typically on site within 48 hours of enquiry, with a fixed written quotation in 5 working days. Our typical garage conversion project in Lewisham costs between £17,000 and £44,000 in 2026, with most Edwardian villas and inter-war semis landing around £30,500. We are FMB, TrustMark, Checkatrade and TrustATrader accredited and operate as a Principal Contractor under CDM 2015.
Strong volume of side-return extensions, mansard lofts and full refurbs across SE13, SE23 and SE4. Working out of London Borough of Lewisham'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 Lewisham project is on Edwardian villas within easy reach of Forest Hill or Telegraph Hill, and we work with a small panel of trusted London-area subcontractors we have used for years.
What's included in our garage conversion price
Up-rated foundations and floor build-up to current insulation standards, masonry infill of the garage opening, new window/door, full insulation to Part L, plasterboard and skim, electrics, heating, flooring sub-base. 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 £2,440–£4,575 in trade markup. We exclude planning fees, party-wall surveyor fees and structural engineer drawings, which we coordinate at cost.
Lewisham planning, party walls and Building Regs
Blackheath and Telegraph Hill conservation areas — match brick course, fenestration and ridge line. Garage floors are usually 100–150 mm below the house floor — plan the new floor build-up early or you will lose ceiling height to the screed. Note that Lewisham 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 Lewisham projects
Garage conversions run 4–6 weeks on site. The biggest constraint is typically getting the new floor level to align with the rest of the house. 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 SE13 postcodes we can have someone on site within 48 hours of a phone call.
Guarantees and after-care
Every project we deliver in Lewisham 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 Lewisham schemes — worth considering for any project above £50,000.
Garage Conversion cost in Lewisham — 2026 price guide
Project size
From
To
Integral single garage
£17,000
£22,000
Attached single garage
£19,000
£24,000
Double garage
£24,000
£31,000
Double + ensuite
£27,000
£37,000
Indicative Lewisham (SE13) ranges for 2026. A site visit firms the figure to +/-5%.
Frequently asked questions
How much does a garage conversion cost in Lewisham in 2026?
Typical Lewisham pricing ranges from £17,000 to £44,000 depending on size, finish and site complexity. Lewisham sits in the mid-band of our delivery area. A free site visit firms the number up to ±5%.
How long will a garage conversion take in Lewisham?
Allow 6–12 weeks of design, planning and procurement before work starts, then a project-dependent build phase. Garage conversions run 4–6 weeks on site. The biggest constraint is typically getting the new floor level to align with the rest of the house. We share a Gantt-style schedule with every quotation.
Does a garage conversion in Lewisham need planning permission?
Most integral garage conversions sit inside Permitted Development as long as the building footprint doesn't change. Detached garages and conservation areas typically need full planning.
Which areas of Lewisham do you cover?
We cover all of SE13 and the surrounding London postcodes from our Dartford base. Recent projects sit close to Forest Hill and Telegraph Hill. 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.