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: Generally available for rear dormers
- Conservation areas: 30 in Lewisham
What does a Lewisham loft conversion cost, and does it need permission?
Lewisham’s Datahub set records 1,442 rear dormer applications at 80% approved and 198 loft applications at 73%. The council issued 1,221 lawful development certificates in three years, so a large share of Brockley and Catford lofts proceed without any application for permission at all.
| Measure | Lewisham | Outcome |
|---|---|---|
| Rear dormer applications in the Datahub | 1,442 | 80% approved |
| Loft conversion applications in the Datahub | 198 | 73% approved |
| Mansard roof applications in the Datahub | 216 | 63% approved |
| Householder decisions | 2,037 | 86.3% approved |
| Lawful development certificates issued | 1,221 | — |
| Householder appeals decided | 313 | 33.2% allowed, median 69 days |
Sources: rows one to three from the Planning London Datahub, retrieved 15 August 2026 — phrase-matched application descriptions, comparable within Lewisham only. Rows four and five from MHCLG PS1 and PS2, twelve quarters to March 2026. Row six from Planning Inspectorate casework decided 2016–2026. Build costs on this page are our own 2026 London range, not a published statistic.
How do Lewisham loft costs break down?
Those figures buy building work and nothing else. What the drawing package covers, what it costs and how long it takes lives on our loft conversions in Lewisham page.
Start with a filing question rather than a price. Lewisham logged 1,221 certificates of lawful development, of all kinds, in the returns it filed with MHCLG for April 2023 to March 2026 — the paperwork householders use to prove a scheme never needed permission. No English district publishes a grant-or-refuse split for those certificates, so read the figure as evidence of how routinely work here proceeds under permitted development, never as a pass rate. Cost is the part that genuinely varies, and it varies by roof form.
Loft conversion build costs in Lewisham
Those are build costs. VAT, professional fees — ours, the structural engineer’s, the party wall surveyor’s — and the council’s fee all sit outside them, and so does the largest local variable, which is what is currently holding your roof up. Lewisham is a strikingly Victorian borough: 27.7% of its 133,880 dwellings predate 1900 against 20.9% across the capital, while only 9.3% date from the 1930s against a London figure of 16.0% (VOA council tax stock at 31 March 2025, published via the London Datastore). That means a purlin-and-rafter roof over a solid-wall house far more often than the trussed roof of an interwar semi. Better to convert, harder to price from the pavement, because until the plasterboard comes down nobody knows what state the timber is in.
Lewisham is one of the better boroughs in London for a dormer and the 20-30 square metres it returns: Brockley, Honor Oak and Forest Hill have well-proportioned Victorian and Edwardian roofs, no borough-wide Article 4 Direction, and a dormer at the upper end of its range is often available under permitted development rather than by application.
Which loft type suits Lewisham properties?
A rear dormer suits the Brockley and Forest Hill terraces and generally needs no structural work beyond the new floor. Catford and Hither Green semis are hipped and want the hip converting to a gable first. Where the property is one of Deptford's post-war blocks, the roof is common parts and the project is a leasehold question rather than a planning one.
Dormer loft conversions
The rear dormer is the default here because the stock is exactly the right shape for it: long uniform Victorian terraces through Brockley, Ladywell, Catford and Hither Green, steep pitches, party walls on both flanks. Kept below the ridge, set back 200mm from the eaves and held inside the 40 cubic metre allowance a terraced house gets, it is normally permitted development, and what you end up holding is a certificate rather than a permission. Two things take it out of that. One is a dormer on the front or on a flank in public view. The other is a conservation area, which in this borough catches many more houses than people expect.
Mansard loft conversions
A mansard replaces the roof rather than adding to it, and since no part of the permitted development order allows a new roof profile, it always needs planning permission. The extra cost buys a full storey with head height across its whole width — 30 to 50 square metres against the 20 to 30 a dormer returns — and a staircase that can land somewhere sensible rather than in a corner. Where Lewisham says yes is usually where someone has already been told yes: on a terrace carrying three mansards in a row, the streetscene argument has been settled by other people and your job is to match them rather than to reopen it.
Hip-to-gable and dormer combinations
A hipped roof wastes the loft. It falls away on the flank and leaves a triangular void with no usable width at exactly the point where a new staircase wants to arrive. Squaring that flank into a full gable and then adding a rear dormer typically returns 25 to 35 square metres. Lewisham has less of this stock than its neighbours, because hipped roofs arrived with the interwar semi and only 9.3% of the borough was built in that decade — so this is a Grove Park, Downham and Bellingham job rather than a Brockley one. On a semi, both halves can be permitted development. The gable must not come forward of the original front wall plane, and because a semi is not a terrace the volume allowance is 50 cubic metres rather than 40.
Velux (rooflight) conversions
Nothing changes outside, which is precisely why this route survives where the others do not. Velux and similar rooflights sit within the existing slope, so the roof keeps its shape and its volume and the work reduces to floor, stair, insulation, fire separation and a means of escape. The constraint is head height and it has to be there already: measure from the ridge board to the top of the ceiling joists and you want roughly 2.4 metres, because the new floor build-up and the insulation each take a slice. Under Class C a rooflight stays permitted development even inside a conservation area, provided it projects no more than 150mm beyond the plane of the slope and sits no higher than the ridge. On the Blackheath and Brockley streets that is often the only conversion still on the table.
Does a Lewisham loft need planning permission?
Lewisham is one of the more straightforward boroughs for a loft. There is no borough-wide Article 4 Direction, 30 conservation areas cover a minority of addresses, and 1,221 lawful development certificates were issued in three years (MHCLG planning statistics, retrieved 1 September 2026). The Victorian and Edwardian terraces of Brockley, Honor Oak and Forest Hill have the ridge height that rear dormers want, and Catford and Hither Green add interwar semis behind them.
Permitted Development for lofts
A rear dormer or a Velux conversion usually proceeds with no planning application at all, because the work sits inside Class B or Class C of the General Permitted Development Order. Four allowances decide whether yours does:
- 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
Conservation areas
Designation removes the dormer outright rather than conditionally, and the distinction matters. Class B of the permitted development order — the class that permits an enlargement of the roof — does not apply on article 2(3) land, and every conservation area is article 2(3) land. So a rear dormer that would be lawful a street outside the boundary needs a full householder application inside it, whether or not a single person can see it. The scale of that in Lewisham is what catches people: Blackheath covers 180.7 hectares, Brockley 115.3, Telegraph Hill 76.1 and Culverley Green 60.5 (planning.data.gov.uk conservation area register, retrieved 1 September 2026). The borough also holds 367 listed buildings, 30 of them Grade II* (Historic England, via the MHCLG Planning Data Platform, retrieved 2 September 2026), and on a listed building a loft conversion is a listed building consent question before it is a planning one.
Mansard planning permission
Mansards always need permission, since the roof's height and shape both change. Lewisham's Victorian and Edwardian terraces through Brockley and Forest Hill generally have ridge height enough that a rear dormer will do, which is cheaper and available under permitted development. The mansard case here is usually about head height at the front of the plan rather than about total floor area.
Lewisham publishes its own pre-application charges. The borough approves 86.3% of householder applications and has no Article 4 Direction (MHCLG planning statistics, retrieved 1 September 2026), so for an ordinary loft the enquiry adds little. Where it earns its cost is on anything that might be read as a deep rear extension, a category Lewisham refuses more heavily than any other London borough.
Our drawing fees for loft conversions in Lewisham
Our drawings are prepared by MCIAT chartered architectural technologists and cover both of the submissions a loft normally needs: the planning application or lawful development certificate first, then the building regulations package that follows. Lewisham is quick on the first of those — 95.3% of its householder decisions landed inside eight weeks, against 92.5% across London (MHCLG planning application statistics, twelve quarters to March 2026, retrieved 1 September 2026). In this borough it is the drawings rather than the council that usually set your start date.
Drawing fees for loft conversions
Each package starts with a measured survey of the house as built and produces existing and proposed floor plans, elevations, sections, a roof plan and a site plan. Mansards additionally get a streetscene elevation and a design and access statement, because a mansard is judged against the row it stands in and a row is easier to draw than to describe. Where the property is listed we prepare the heritage material for the consent application too — Lewisham granted 94 of the 98 listed building consents to alter or extend that it decided over three years, one of the higher rates in London. Our fees run around 30% under typical London architect rates for the same scope.
Our surveyors work the whole borough, from Blackheath across to Brockley, Catford and Sydenham: SE3, SE4, SE6, SE8, SE12, SE13, SE14, SE23, SE26.
Frequently asked questions
How much does a loft conversion cost in Lewisham?
Roof form drives the number far more than floor area does. A rear dormer in Lewisham builds out at roughly £45,000 to £65,000; a mansard at £70,000 to £110,000; a Velux scheme that adds rooflights and nothing else at £25,000 to £38,000. Construction only — drawings, structural calculations and the council fee sit outside those ranges.
Do I need planning permission for a loft conversion in Lewisham?
On most Lewisham addresses, yes. Nothing here is covered by an Article 4 Direction, so a rear dormer that respects the allowance and sits away from the road normally proceeds unpermitted, and the borough's certificate count reflects how routinely that route is used. Mansards need an application. Note that Lewisham is unusually hard on deep rear extensions — but that restriction does not carry across to roof work.
What is the minimum head height for a loft conversion in Lewisham?
Brockley, Honor Oak and Forest Hill are among the better-proportioned Victorian and Edwardian roofs in south London and usually have it comfortably, which is why so much loft work here proceeds under permitted development. Over in Catford and Hither Green the interwar semis only make the figure at the very peak, so the hipped end has to come off first.
Do I need a Party Wall Agreement for a loft conversion in Lewisham?
Because Brockley and Honor Oak are terraced almost continuously, a Lewisham loft usually needs notice to two neighbours rather than one. The 1996 Act gives each of them two months and the right to appoint a surveyor at your expense if they dissent. On the Catford semis it is a single notice, and the hip-to-gable raises the wall as well as loading it.
Can I get a mansard loft conversion approved in Lewisham?
Mansards get judged one street at a time. Officers look at what the roofline already does: whether the terrace keeps an unbroken eaves line, whether a conservation area designation bites, and whether a neighbour has already built one. Across the three years of returns ending last March the council issued 4,264 decisions and granted 3,556 of them, so roughly one application in six is refused — and a mansard that matches a built precedent on the same terrace is usually arguable.
