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: 45 in Wandsworth
What does a Wandsworth loft conversion cost, and which form wins?
Wandsworth is a mansard borough: 2,310 mansard applications at 87% approved, against 986 rear dormers at 81%. That matters to the budget, because a mansard rebuilds the roof rather than adding to it. The council approved 91.3% of householder applications overall.
| Measure | Wandsworth | Outcome |
|---|---|---|
| Mansard roof applications in the Datahub | 2,310 | 87% approved |
| Rear dormer applications in the Datahub | 986 | 81% approved |
| Householder decisions | 3,107 | 91.3% approved |
| Decided inside eight weeks | 85.8% | 5.9% beyond thirteen weeks |
| Conservation areas | 46 | 1,061 hectares |
| Mansard drawing package | from £1,575 | our fixed fee |
Sources: rows one and two from the Planning London Datahub, retrieved 15 August 2026 — phrase-matched descriptions, comparable within Wandsworth only. Rows three and four from MHCLG PS1 and PS2, twelve quarters to March 2026. Row five from planning.data.gov.uk, retrieved 1 September 2026. Row six is our own published fixed fee. Build costs elsewhere on this page are our 2026 London range, not a published statistic.
What does a Wandsworth loft cost by roof type?
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Loft type drives the build cost far more than the address does. Wandsworth sits mid-table for London loft pricing, well above the cheapest outer boroughs and nowhere near the top, so the comparison worth making is dormer against mansard rather than borough against borough.
Loft conversion build costs in Wandsworth
Build cost is not the whole bill. Council charges sit outside it, and so do professional fees: the drawings, the structural engineer, and a surveyor under the Party Wall Act should an adjoining owner dissent. Within the build, four variables move the number more than any others — how many square metres the loft yields, how expensive the fit-out is, what the roof structure demands in steel, and how close to the front door a lorry can actually park.
The Victorian terraces between the commons are consistently well proportioned, so a dormer reliably delivers the 20-30 square metres it promises - the figure holds up here better than in most of inner London - and the form is settled enough that neighbouring examples are usually visible from your own garden. Southfields' semis need a hip-to-gable before those numbers apply.
Which loft type suits Wandsworth properties?
The established form on the Victorian terraces is a rear dormer, held down from the ridge line and kept in from both flank walls. The Edwardian villas around Wandsworth and Clapham Commons have more depth and more scrutiny, sitting within the borough's 45 conservation areas. Southfields' interwar semis need the hip taking off before the ridge is usable.
Dormer loft conversions
Long terraced streets are the borough's dominant form and the rear dormer is what they take. On a Victorian or Edwardian mid-terrace a flat-roofed rear dormer usually returns 20 to 30 square metres of floor. It holds its permitted-development status while it stays under the ridge line and keeps its setback from the eaves, which is why most lofts here never meet a planning officer at all. Inside a conservation area a dormer visible from the highway needs full permission instead.
Mansard loft conversions
Mansards take the existing slope away and put a near-vertical face with a shallow top in its place, adding a full storey with standing height right across it. Because the roof form itself changes, this always requires planning permission. Wandsworth judges each on design quality, effect on the streetscene, and conservation area status. The trade is plain enough: more money and more usable floor, in exchange for a decision you have to win rather than a certificate you can simply claim.
Hip-to-gable and dormer combinations
Semi-detached and detached houses across the borough often carry a hipped roof, which wastes the loft at one end. A hip-to-gable squares that end into a full gable; put a rear dormer with it and 25 to 35 additional square metres is the usual outcome. Semi-detached houses can take that route as permitted development, provided the new gable stops short of the front wall plane the house already has.
Velux (rooflight) conversions
A Velux conversion is the cheapest and least disruptive route, though everything hinges on the loft already standing tall enough to inhabit. Rooflights bed into the slope that is there; the profile of the roof, seen from the pavement, does not move at all. That is precisely why the option suits the 45 conservation areas Wandsworth has designated, where altering a visible roofline is the hardest thing to argue for. You give up floor area against a dormer or a mansard, and get back a scheme almost nobody objects to.
Does a Wandsworth loft need planning permission?
Wandsworth is the classic London terrace borough, and its Victorian streets between the commons have produced enough loft conversions that the form is well settled. The council approves 91.3% of householder applications but decides only 85.8% inside eight weeks, with 5.9% running past thirteen (MHCLG planning statistics, retrieved 1 September 2026). Expect a yes, and expect to wait longer for it than the statutory target suggests.
Permitted Development for lofts
A rear dormer or a Velux conversion in Wandsworth is normally permitted development, so there is no application and no decision to wait on. That matters more when you see how the borough handles the other permitted-development route: only 143 prior-approval applications for larger rear extensions were determined here between April 2023 and March 2026, and 29 of them were refused, close to one in five. Lofts sidestep that process altogether, so long as they meet these conditions:
- 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
Wandsworth has Article 4 Directions in place. Article 4 for HMO conversions covering the whole borough. 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
Forty-five conservation areas cover parts of Wandsworth, among them Wandsworth Common, Clapham Common West, Tonsley, Magdalen Park and Nightingale Triangle. Designation does not stop a loft; it changes the route. A rear dormer may still be permitted development, anything on a front or side slope in public view will not be, and the conservation officer will have a view on materials and window proportions. Mansards inside a designated area get read against that area's own character appraisal and management plan — both published, and both worth reading before anyone draws a line.
Mansard planning permission
Since a mansard lifts the roof line and alters its profile, an application is unavoidable. Wandsworth's Victorian terraces between the commons carry enough existing examples that a new one argues from an established pattern. The borough approves 91.3% of householder applications (MHCLG planning statistics, retrieved 1 September 2026), so the likely obstacle is not refusal but the programme - only 85.8% are decided inside eight weeks.
Wandsworth publishes its own pre-application charges. Weigh them against what the enquiry buys here: consent is close to assured, so the value is in the calendar rather than the outcome, and pre-application advice lengthens the run-up rather than shortening the determination. On a conservation-area address with 45 designations in the borough, it is still usually worth it.
Our drawing fees for loft conversions in Wandsworth
We do. Chartered technologists here (MCIAT) prepare the full submission set. That means the planning application in the cases that need one, plus a building regulations package in every case, because no loft is exempt from that second approval even when it escapes the first.
Drawing fees for loft conversions
Every package carries a measured survey first. Then floor plans and elevations for existing and proposed, a plan of the roof, sections through it, and the site plan. Two extra documents attach to a mansard: a design and access statement, and an elevation of the whole street showing your roof among its neighbours, because that comparison is the one an officer will make anyway. Our figure for the full list comes in near enough 30% under London architect rates.
We work across all seven Wandsworth districts: SW8, SW11, SW12, SW15, SW17, SW18, SW19.
Frequently asked questions
How much does a loft conversion cost in Wandsworth?
Build costs in Wandsworth fall into a fairly narrow band by loft type. A rear dormer is generally quoted at £45,000 to £65,000, a mansard at £70,000 to £110,000, and a Velux conversion, which leaves the roof shape untouched, at £25,000 to £38,000. Those are contractor build figures from jobs we draw, not published statistics, and they carry no design or council fees. Set them against what the asset is worth: 4,984 Wandsworth homes changed hands in 2025 at a median of £650,000 on the Land Registry's price-paid file, the same median it recorded for 2024.
Do I need planning permission for a loft conversion in Wandsworth?
Check the Article 4 Direction and the 45 conservation areas first, because between them they reach a large share of the terraced streets where lofts are most wanted. Outside their coverage, a rear dormer within the volume allowance and off the principal elevation is normally permitted, and Wandsworth issued 975 lawful development certificates over three years (MHCLG planning statistics, retrieved 1 September 2026). A mansard needs an application anywhere.
What is the minimum head height for a loft conversion in Wandsworth?
The Victorian terraces between the commons are consistently well proportioned in this respect, which is why the rear dormer is such a settled form on these streets. Interwar semis in Southfields hit the number only under the peak, and squaring off the hip is what turns that into a usable room.
Do I need a Party Wall Agreement for a loft conversion in Wandsworth?
Two adjoining owners on a mid-terrace Wandsworth house, one on a Southfields semi. The statutory notice period is two calendar months, and on streets where several conversions have already been done the neighbours will usually know the process — which tends to make agreement quicker rather than slower. Budget for surveyors anyway; dissent is a right, not an objection.
Can I get a mansard loft conversion approved in Wandsworth?
Wandsworth publishes no mansard policy, which cuts both ways — nothing forbids one, nothing guarantees one. Four things end up carrying the decision: what the addition does to the view along the street, whether a designation applies, how convincingly the detail has been resolved, and which roofs on the same terrace already carry consent. That last one is the strongest single item in a Wandsworth file.
