Rooflight Loft Conversion Cost in London: 2026 Prices and What Drives Them
Last updated: 6 November 2026
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A rooflight conversion is the simplest form of loft conversion: nothing is built out of the roof, the roofline does not change, and the space is the space already there, lit by windows in the existing slope. Our loft conversion cost guide calls it the cheapest type, and the one that adds the least usable floor area, because headroom is limited by the pitch.
In 2026 we publish £1,500–£2,000 per m² including VAT for a rooflight-only conversion, or £30,000–£40,000 for a 20 m² example nationally. London sits above the national rates at our published 30–50% premium, with size bands of £39,000–£60,000 at 20 m², £58,500–£90,000 at 30 m² and £78,000–£120,000 at 40 m². Those bands are published by floor area, not by type.
Table of Contents
- What a rooflight conversion is
- Floor area
- Roof windows
- Planning permission
- Party wall and structure
- Building regulations
- What drives the cost
- Fees
- Timeline
- Assumptions
What a Rooflight Conversion Is
Rooflight-only means the roof shape stays exactly as it is. The windows go into the slope you already have, so nothing changes from the street and nothing is added to the building. Inside, the new room is the loft floor with the existing pitch as its ceiling.
The difference from a dormer is structural. A dormer builds a framed box out of the slope for full headroom, which is why our dormer loft conversion guide publishes a higher rate and a larger example. A hip to gable changes the end of the roof; a mansard replaces the slope.
| Type | Published rate per m² (inc. VAT) | Published example | What it changes |
|---|---|---|---|
| Rooflight-only | £1,500–£2,000 | £30,000–£40,000 at 20 m² | Windows in the existing slope; no change to the roofline |
| Dormer | £1,800–£2,500 | £54,000–£75,000 at 30 m² | A framed box out of the rear slope |
| Hip to gable | £2,000–£2,800 | £70,000–£98,000 at 35 m² | The hipped end becomes a gable wall |
| Mansard | £2,200–£3,000 | £88,000–£120,000 at 40 m² | The slope is replaced with a steep wall and flat section |
The ordering is consistent: each step up the list buys floor area by changing more of the building. The cost guide carries the same four rows; the calculator applies the London bands by area.
Where the Floor Area Comes From
The published example is 20 m², the smallest of the four, and it is the area already under the roof; what changes is how much of it has headroom. Our guide publishes 2.2 m at the highest point, and where the loft falls short it lists lowering the ceiling below or raising the roof, both adding significant cost.
Read a rooflight quote as usable width first, floor area second: our guide says a rooflight conversion may be enough if you only need a home office or an extra bedroom.
The London bands are not split by type, so the figure to carry is the rooflight rate plus the London band for your floor area — as the calculator does.
Roof Windows: How Many, and What They Cost
Our guide publishes £800–£1,500 per roof window, supplied and fitted including VAT; the number is a survey decision, and we publish no fixed count per square metre.
One question worth asking of any quote: the guide's inclusions list names windows, while its cost-driver list prices them separately. At the upper end of the range, ask whether they are inside the rate or added per window.
Does a Rooflight Conversion Need Planning Permission?
For a house, usually not. A rooflight conversion adds no enclosed volume and raises nothing above the existing roof, so the volume and height tests are rarely the obstacle. Our guide sets out the conditions: no more than 40 m³ of extra roof space on a terrace (50 m³ otherwise), nothing above the existing roof line, and side-facing windows obscure-glazed and non-opening unless the openable parts sit above 1.7 m.
Conservation areas, listed buildings and areas of outstanding natural beauty restrict or remove permitted development, and flats are outside the house rules; the dependable answer for a specific address is an informal check or a lawful development certificate.
Our planning permission cost and timeline guide covers the householder application (£206), the full application (£462) and London timings.
Party Wall and Structural Work
A rooflight conversion is the lightest of the types, but not automatically party wall-free: the Party Wall etc. Act 1996 applies to work on or next to a party structure, and roof structure and covering between terraced houses is exactly that. A party structure notice is due at least two months before work, and our guide publishes £700–£2,000 for an agreement.
Ask at survey whether a notice is needed. Structurally the job is about the existing roof: the guide lists a traditional cut roof as easier and cheaper to convert than a trussed rafter roof.
Building Regulations
Approval is separate from planning and still applies: structure around the openings, fire safety and escape, energy efficiency, and the stair and its headroom. Our guide publishes £200–£1,000 for approval and £300–£700 for inspection.
What Drives the Cost
| What changes the number | Published figure |
|---|---|
| Floor area | London bands: £39,000–£60,000 at 20 m², £58,500–£90,000 at 30 m², £78,000–£120,000 at 40 m² |
| Headroom | Below 2.2 m at the highest point, the options are lowering the ceiling below or raising the roof, both significant added cost |
| Roof windows | £800–£1,500 each, supplied and fitted |
| Roof structure | A traditional cut roof is easier and cheaper than a trussed rafter roof |
| Staircase | £1,000–£2,500 straight; £3,000–£7,000 spiral or bespoke; +£2,000–£5,000 to alter the floor below |
| Bathroom | £5,000–£12,000, before the soil pipe route is priced |
| Finish | Premium finishes add £10,000–£25,000 |
| Access | Scaffolding £1,000–£3,000, priced at survey |
Published Fees
The build price is not the whole budget.
| Fee | Published figure |
|---|---|
| Planning application, householder / full | £206 / £462 |
| Building regulations approval / inspection | £200–£1,000 / £300–£700 |
| Party wall agreement | £700–£2,000 |
| Structural engineer | £500–£2,000 |
| Architect fees / contingency | 5–10% of build cost / 10–15% of budget |
| Scaffolding | £1,000–£3,000 |
Budget a margin. Our guide advises adding 15–20% on top of a quoted build cost to cover fees, contingency and unexpected findings.
How Long Does a Rooflight Conversion Take?
Our guide publishes 4–6 weeks of construction, the shortest of the types, with 4–8 weeks of design and planning first. In London the consent stage is usually the variable.
Assumptions Behind These Figures
Every figure is restated from our loft conversion cost guide or the loft conversion cost calculator, including VAT at 20% and excluding professional fees, planning fees and premium fixtures unless stated. The rate and the 20 m² example are the guide's published rooflight rows; the London bands are published by floor area, not by type. We publish no rooflight-specific London band and no measured average for the floor area gained.
Frequently Asked Questions
How much does a rooflight loft conversion cost in London in 2026?
£1,500–£2,000 per m² including VAT, or £30,000–£40,000 for a 20 m² example nationally. London adds our published 30–50% premium: £39,000–£60,000 at 20 m², £58,500–£90,000 at 30 m² and £78,000–£120,000 at 40 m², published by floor area rather than by type.
Is a rooflight conversion the cheapest type?
Yes, on our published rates: £1,500–£2,000 per m² against £1,800–£2,500 for a dormer, £2,000–£2,800 for a hip to gable and £2,200–£3,000 for a mansard. It also adds the least usable floor area, because headroom is set by the existing pitch.
Do I need planning permission for a rooflight conversion?
For a house, usually not: no enclosed volume is added and nothing rises above the existing roof, so the volume and height tests are rarely the obstacle. Conservation areas, listed buildings, areas of outstanding natural beauty, flats and Article 4 directions change that; a lawful development certificate settles a specific address.
How much headroom do I need?
Our guide publishes 2.2 m at the highest point. Where the loft falls short, the options are lowering the ceiling below or raising the roof, both of which add significant cost.
How many roof windows, and what do they cost?
Our guide publishes £800–£1,500 per roof window supplied and fitted. The number is a survey and design decision, and we publish no fixed count per square metre.
Will a rooflight conversion add value?
Our guide publishes 15–20% for loft conversions generally, not for this type specifically, and it moves with the street, the room count and the finish.
Can I add a bathroom to a rooflight conversion?
Yes in many layouts. Our guide publishes £5,000–£12,000, and the soil pipe route to the existing stack usually decides it.
How long does a rooflight conversion take?
Our guide publishes 4–6 weeks of construction, the shortest of the types, with 4–8 weeks of design and planning first.
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Still comparing types? Read the cost guide, compare a dormer or a mansard, or get a floor-area figure from the calculator. For the wider view, see our loft conversion service in London.
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