Loft Conversion Types
Velux & Rooflight Loft Conversions
The cheapest and least disruptive conversion there is — because nothing about the shape of your roof changes. It only works if the height is already up there.
The Conversion that Doesn't Change the Roof
Every other type on this site alters the roof — building it out, filling it in, or replacing it. A rooflight conversion doesn't. The roof stays exactly as it is, and windows are fitted flush into the existing slope.
Everything else happens inside: a proper floor, insulation, a staircase, plastering, electrics, and the fire protection that turns a loft into a habitable room.
That makes it the cheapest conversion by a wide margin, the quickest, and the least likely to involve a planning application. It's the honest answer to “can you do a loft conversion for £20,000?” — the answer being: sometimes, at the very bottom of this type, and only on a loft that already has the height.
Because that's the catch, and it's a real one. A rooflight conversion adds no headroom whatsoever. If you can't stand up in your loft now, this conversion won't change that.
Does Your Loft Have the Height?
There Is No Legal Minimum Loft Height
What there is, is a building regulation requiring at least 2 metres of headroom over the whole of the staircase and landings — 1.9 metres may be accepted over part of the stair in some circumstances. Work back from that and you get the industry's rule of thumb: roughly 2.2 to 2.4 metres from the top of the ceiling joists to the underside of the ridge. It is a rule of thumb, not a regulation.
You're a Good Candidate
If you measure over about 2.4 metres and the roof is a traditional cut-timber structure with clear space under the ridge.
You're Borderline
Between roughly 2.2 and 2.4 metres. Options exist — lowering the ceiling below, or accepting a lower finish — but they change the cost.
You Aren't, if the Roof Is Trussed
Modern W-shaped trussed rafters fill the loft with timber and can't simply be cut out; converting one means replacing the structure, which pushes you into a different type and a different price entirely. And permitted development rights don't apply to flats or maisonettes at all.
What the Work Involves
Strengthening the Floor
Ceiling joists hold up a ceiling; they don't carry people and furniture. New floor joists go in alongside or above them.
Rooflights
Fitted flush into the existing slope. Under permitted development they must not protrude more than 0.15 metres beyond the plane of the roof, and must not sit above the highest part of the roof.
The Staircase
A permanent stair with 2 metres of headroom. On a small landing this is often the single hardest constraint, and it's what turns some “obvious” rooflight conversions into non-starters.
Insulation
Between and over the rafters, to current standards. This is a bigger job than it sounds and it's where a cheap quote usually cuts.
Fire Safety
Even the simplest conversion needs it: 30-minute fire-resisting floor, protected stairway, fire doors, interlinked mains-powered smoke alarms at every level.
What a Rooflight Conversion Costs
| Scope | Typical West London range |
|---|---|
| Rooflight conversion, single room | £22,000 – £32,000 |
| With a small shower room | £28,000 – £40,000 |
These are estimates for West London, not quotes. What your loft actually costs depends on your roof, your access and what you put in the room — which is exactly what a survey is for.
On the £20,000 question: it's occasionally achievable at the very bottom of this range, on a loft with generous existing height, easy stair access, no bathroom and a simple finish. It is not achievable for a dormer or a hip to gable in West London, and any quote suggesting otherwise is worth reading twice.
Rooflights and Planning
This is the one type where a conservation area doesn't automatically stop you — and it's a distinction worth understanding, because almost nobody explains it.
Under permitted development, roof enlargements (dormers, hip to gables, mansards) and other roof alterations (rooflights) are treated as two different things. Enlargements are not permitted on designated land such as a conservation area. Rooflights are covered by a different class, which carries no such exclusion — so a flush rooflight conversion can still be permitted development in a conservation area, provided it stays within 0.15 metres of the roof plane and below the ridge.
But check your address before relying on that. An Article 4 direction can remove that right too, and in Ealing several do. Bedford Park's direction removes both roof enlargements and “any other alteration to the roof of a dwelling house” — which means rooflights included.
Building regulations approval is always required, planning permission or not.
Rooflight Conversion Conversions Across West London
Best suited to houses with generous existing loft height — often the larger inter-war and Edwardian stock:
Rooflight Conversion Questions
Is this the cheapest type of loft conversion?
Yes, comfortably — because the roof structure doesn't change and there's no external building work. The saving comes with a hard condition attached: your loft needs the height already.
How do I measure whether my loft is tall enough?
From the top of the existing ceiling joists to the underside of the ridge, at the highest point. Over about 2.4 metres and you're in good shape; under about 2.2 and you're likely looking at a dormer instead.
Can I convert a loft with modern roof trusses?
Not as a rooflight conversion. W-shaped trussed rafters fill the space and are structural, so removing them means replacing them — a different job, a different budget, and one worth getting a structural opinion on before anything else.
Find Out What a Rooflight Conversion Would Cost
Five questions, two minutes, no obligation.