TL;DR — Key Facts
- Dormer loft conversion: £45,000 – £65,000 (inner London borough)
- Mansard conversion: £70,000 – £110,000
- Velux conversion: £25,000 – £38,000
- Planning permission: Restricted by Article 4 in some areas
- Conservation areas: 64 in Lambeth
What does a Lambeth loft conversion cost, and which form?
Dormer and mansard both, in volume. Lambeth’s Datahub set records 2,406 rear dormer applications at 77% approved and 1,404 mansards at 70%. A mansard rebuilds the roof rather than adding to it, which is where the budgets separate. The borough also holds 223 Article 4 areas in the register.
| Measure | Lambeth | Outcome |
|---|---|---|
| Rear dormer applications in the Datahub | 2,406 | 77% approved |
| Mansard applications in the Datahub | 1,404 | 70% approved |
| Loft conversion applications in the Datahub | 554 | 83% approved |
| Conservation areas | 65 | 863 hectares |
| Article 4 areas in the register | 223 | third most of the 16 boroughs in the Article 4 register |
| Mansard drawing package | from £1,575 | our fixed fee |
Sources: Datahub rows from the Planning London Datahub, retrieved 15 August 2026 — phrase-matched descriptions, comparable within Lambeth only; registers from the MHCLG Planning Data Platform, retrieved 1 September 2026; the package fee is our own published fixed fee. Build costs on this page are our own 2026 London range and are an estimate, not a published statistic.
What does a Lambeth loft cost by roof type?
Ready to move from budgeting to drawings?
Loft conversion build costs in Lambeth depend primarily on the type of conversion. As an inner London borough, Lambeth sits in the mid-range of London loft conversion pricing.
Loft conversion build costs in Lambeth
These figures are build costs only and do not include professional fees (architect, structural engineer, Party Wall surveyor) or council fees. The actual cost will depend on the size of your loft, the specification of the fit-out, the structural complexity, and access constraints.
The Victorian terraces of Clapham, Brixton and Herne Hill take a dormer comfortably, at the 20-30 square metres that form usually returns. Kennington's Georgian houses are mansard stock. With 64 conservation areas, though, the achievable figure on any given address is set by the designation before it is set by the roof.
Which loft type suits Lambeth properties?
On a Clapham or Herne Hill terrace a rear dormer is the standard form, detailed to sit below the ridge and set in from the party walls. Kennington's Georgian houses have parapets and want a mansard, with all the consent that implies. On the Streatham estates the roof form usually rules the project out before any planning question arises.
Dormer loft conversions
Lambeth has extensive streets of terraced housing, making rear dormer loft conversions the most popular option. A flat-roof rear dormer on a Victorian or Edwardian mid-terrace can add 20-30 square metres of living space. Rear dormers on terraced houses generally fall under Permitted Development, provided they do not exceed the highest part of the existing roof and are set back from the eaves. Properties in conservation areas may need full planning permission for dormers visible from the highway.
Mansard loft conversions
Mansard conversions replace the existing roof slope with a near-vertical front and a shallow-sloped top, creating a full additional storey. Mansard conversions always require planning permission as they alter the roofline. In Lambeth, mansard conversions are assessed on a case-by-case basis, with design quality, streetscene impact, and conservation area status being key considerations. Mansard conversions are more expensive than dormers but create significantly more usable floor area with full standing head height throughout.
Velux (rooflight) conversions
A Velux or rooflight conversion is the simplest and most affordable option, suitable where there is already sufficient head height in the existing loft space. Rooflights are installed into the existing roof slope without changing its shape. This type of conversion almost always falls under Permitted Development and is particularly suitable for properties in Lambeth's 64 conservation areas where changes to the roofline may not be acceptable. The trade-off is less usable floor area compared to a dormer or mansard.
Does a Lambeth loft need planning permission?
Lambeth has 64 conservation areas, second only to Richmond upon Thames, so the odds are that your address is inside one and the loft is a permission question rather than a permitted development one. The stock is largely Victorian terrace through Clapham, Brixton and Herne Hill, with Georgian in Kennington and post-war estates in parts of Streatham. Only the first two of those are realistic conversion candidates.
Permitted Development for lofts
Most rear dormer and Velux loft conversions fall under Permitted Development and do not require a planning application. The key PD conditions are:
- The dormer must not exceed the highest part of the existing roof
- The dormer must be set back at least 200mm from the eaves
- Materials must be similar in appearance to the existing house
- No verandas, balconies, or raised platforms
- Side-facing windows must be obscure-glazed and non-opening below 1.7m
- Volume limit: 40 cubic metres for terraced houses, 50 cubic metres for others
Article 4 Directions
Lambeth has Article 4 Directions in place. Borough-wide Article 4 for HMO conversions; plus office-to-residential restrictions. While most Article 4 Directions in London target HMO conversions or commercial changes of use rather than loft conversions directly, it is important to check whether any specific restrictions apply to your property. We verify this as part of our initial assessment.
Conservation areas
Lambeth has 64 conservation areas, including Clapham Common, Herne Hill, Brixton Road, Kennington, Brockwell Park, Streatham Hill. In conservation areas, Permitted Development rights for loft conversions are more restricted. Front-facing dormers and side-facing dormers visible from the highway generally require planning permission. Rear dormers may still qualify as PD, but the conservation officer may have views on materials and design. Mansard conversions in conservation areas are assessed against the area's character appraisal and management plan.
Mansard planning permission
A mansard requires permission wherever it is built. In Lambeth the form fits Kennington's Georgian houses, which have parapets and shallow roofs, more than the Victorian terraces of Clapham and Brixton where a rear dormer is generally sufficient. With 64 conservation areas - second only to Richmond - the designation covering your street is usually the deciding factor.
Take the fee from Lambeth's own published pre-application scale. With designation this widespread, the enquiry is most useful for establishing what the relevant conservation area appraisal expects of a roof addition before the design is fixed. Lambeth withdrew 335 applications in three years (MHCLG planning statistics, retrieved 1 September 2026), and a withdrawal costs the fee and the drawings both.
Our drawing fees for loft conversions in Lambeth
At Architectural Drawings London. Our MCIAT chartered architectural technologists prepare everything needed for planning submission (where required) and building regulations approval.
Drawing fees for loft conversions
Every package includes a measured survey, existing and proposed floor plans and elevations, roof plan, sections, and a site plan. For mansard conversions, we also prepare a design and access statement and streetscene elevation. Our fees are 30% below typical London architect rates for the same scope of work.
We cover all Lambeth postcodes: SE1, SE11, SE24, SE27, SW2, SW4, SW8, SW9, SW16.
Frequently asked questions
How much does a loft conversion cost in Lambeth?
Loft conversion costs in Lambeth vary by type. A rear dormer loft conversion typically costs £45,000 to £65,000. A mansard conversion costs £70,000 to £110,000. A Velux (rooflight only) conversion costs £25,000 to £38,000. These are build costs only.
Do I need planning permission for a loft conversion in Lambeth?
Inside the 64 conservation areas, generally not, and Lambeth also operates an Article 4 Direction covering conversions to houses in multiple occupation. Outside a designated area, a rear dormer within the volume allowance away from the highway remains available. The borough issued 1,138 lawful development certificates in three years (MHCLG planning statistics, retrieved 1 September 2026), which is the route for confirming that position in writing.
What is the minimum head height for a loft conversion in Lambeth?
The Victorian terraces of Clapham, Brixton and Herne Hill generally have it. Kennington's Georgian houses have parapets and shallow roofs where the measurement does not apply, and the Streatham estates frequently have a roof structure that rules the job out before height is even considered.
Do I need a Party Wall Agreement for a loft conversion in Lambeth?
Lambeth's terraced stock means most conversions here are notifiable on both flanks. The Party Wall etc. Act 1996 requires a separate notice to each adjoining owner, two months ahead, covering both the beam seatings and any raising of the wall. Where the property is a flat carved out of one of the larger Clapham houses, the freeholder's licence to alter comes first and frequently determines whether the project happens at all.
Can I get a mansard loft conversion approved in Lambeth?
Lambeth assesses mansard applications on a case-by-case basis. Lambeth Council will consider the impact on the streetscene, conservation area status, design quality, and any existing precedents on your street.
