TL;DR — Key Facts
- Build cost per sqm: £2,500 – £3,800 (inner London borough)
- Council planning fee: £548 (householder application, 2026)
- Typical projects: rear extension, side-return, two-storey, wraparound
- Conservation areas: 64 designated areas in Lambeth
- Permitted Development: Restricted by Article 4 in some areas
Extension costs in Lambeth
Costs here are build costs. For the drawing package itself — scope, fee and timeline — see house extensions in Lambeth.
House extension build costs in Lambeth typically range from £2,500 to £3,800 per square metre, reflecting Lambeth's position as an inner London borough. These figures cover the construction cost only and do not include professional fees, planning fees, or VAT.
With 64 conservation areas, most Lambeth extensions are being detailed to a conservation officer's expectations rather than to a builder's default. Matched stock brick and a properly resolved junction with the original rear elevation are the items that move a quote upward. On the Streatham estates the driver is different again - existing construction that a rear addition has to tie into cleanly.
Typical extension costs in Lambeth (build only)
On top of the build cost, you will need architectural drawings. These fees are 30% below typical London architect rates.
What affects extension costs in Lambeth
Lambeth has 64 conservation areas, second only to Richmond, so most addresses are inside one and the design is being assessed rather than merely checked. Its Victorian terraces are the classic side-return extension stock, and side-return work has a particular characteristic: the extension occupies the only route to the rear, so access and workspace are the same ground and the sequence has to be planned around that.
Conservation areas
Lambeth has 64 designated conservation areas, including Clapham Common, Herne Hill, Brixton Road, Kennington, Brockwell Park, Streatham Hill. If your property is in a conservation area, Permitted Development rights are restricted, meaning you may need a full planning application (£548 council fee). Conservation area applications also tend to require higher-quality materials and more sympathetic design, which can increase build costs by 10-20%.
Article 4 Directions
Lambeth has Article 4 Directions in place. Borough-wide Article 4 for HMO conversions; plus office-to-residential restrictions. Where Article 4 applies, works that would normally be Permitted Development require a full planning application. This adds £548 to the council fee and typically 2-3 months to the project timeline, which can affect overall costs if you are renting alternative accommodation during the build.
Property type
The housing stock in Lambeth is predominantly victorian terraces in clapham, brixton, herne hill; edwardian villas; 1930s and post-war estates in parts of streatham; georgian in kennington. Victorian and Edwardian terraces typically suit side-return and rear extensions, while 1930s semi-detached properties are well suited to two-storey rear extensions. Detached houses offer the most flexibility but often have larger footprints, meaning higher absolute costs even if the per-sqm rate is similar.
Access and logistics
On a Clapham, Brixton or Herne Hill terrace the side return is both the site and the access, so materials and spoil travel via the hallway right up to the point the structural opening is cut. That is a well-understood sequence and local builders price it routinely, but it is not comparable to a suburban semi with a side gate. The Streatham estates have better vehicle access and different constraints entirely.
Our drawing fees for Lambeth extensions
At Architectural Drawings London. No hourly billing, no surprises. Our fees cover everything needed for a valid planning submission to Lambeth Council and for building regulations approval.
Drawing fees for extensions in Lambeth
Every package includes a measured survey of your existing property, existing floor plans and elevations, proposed floor plans and elevations, a site plan, and a design and access statement where required. Our MCIAT chartered architectural technologists handle the full process from survey to submission, and we liaise with Lambeth Council on your behalf.
We cover all Lambeth postcodes: SE1, SE11, SE24, SE27, SW2, SW4, SW8, SW9, SW16.
Planning vs Permitted Development in Lambeth
Many house extensions in Lambeth can be built under Permitted Development (PD) rights without needing a planning application. Under PD, single-storey rear extensions can extend up to 6 metres from the original rear wall for terraced and semi-detached houses, or 8 metres for detached houses (under the Prior Approval process). However, Lambeth has Article 4 Directions that may remove some PD rights. Borough-wide Article 4 for HMO conversions; plus office-to-residential restrictions.
With 64 conservation areas, second only to Richmond, most Lambeth addresses are designated. The side-extension prohibition has little to act on across the Clapham, Brixton and Herne Hill terraces; the restrictions that operate are on rear depth and on materials. Lambeth also runs an Article 4 Direction covering conversions to houses in multiple occupation.
Two-storey extensions require full permission. With 64 conservation areas - second only to Richmond in London - the odds are that the designation covering your street, and the appraisal document behind it, will decide what the rear elevation may do. On the Clapham and Herne Hill terraces the practical form is a first floor above the existing back addition rather than across the full rear wall.
Lambeth issued 1,138 certificates of lawful development across three years (MHCLG planning statistics, retrieved 1 September 2026). With 64 designated areas the certificate route is unavailable on many addresses, so where your property does sit outside a conservation area boundary, confirming that in writing is worth doing while the survey is fresh rather than years later at sale.
Frequently asked questions
How much does a house extension cost in Lambeth?
Build costs for a house extension in Lambeth typically range from £2,500 to £3,800 per square metre, as Lambeth is an inner London borough. A typical single-storey rear extension of 15-20 sqm would cost between £37,500 and £76,000 for the build alone. On top of build costs.
Can I extend under Permitted Development in Lambeth?
With 64 conservation areas, second only to Richmond, most Lambeth addresses are inside one and the practical restriction is on the rear elevation and roofline rather than on side extensions, because the protected stock is overwhelmingly terraced and the fronts are already uniform. Lambeth also operates an Article 4 Direction covering conversions to houses in multiple occupation.
How long does a house extension take in Lambeth?
A typical house extension project in Lambeth takes 5-8 months from initial instruction to completion. This breaks down as: 2-3 weeks for measured survey and drawing preparation, 8 weeks for planning determination by Lambeth Council (if required), 2-4 weeks for building regulations approval, and 8-16 weeks for construction depending on the size and complexity of the extension.
Do I need a Party Wall Agreement for an extension in Lambeth?
A side-return extension typically builds up to or off the boundary wall on one side while excavating close to the neighbour on the other, so the statute is triggered on two counts and by two separate neighbours. Serve early - a month for excavation, two for line-of-junction and wall work - because the periods run independently of the planning timetable.
What experience do you have with extensions in Lambeth?
We prepare extension drawings for properties across all Lambeth postcodes (SE1, SE11, SE24, SE27, SW2, SW4, SW8, SW9, SW16). Our MCIAT chartered architectural technologists understand Lambeth Council's policies, design guides, and local precedents. We have a council-ready drawing review across all 33 London boroughs.
