Costs & Guides
Loft Conversion Cost in London: 2026 Guide
What a loft conversion actually costs in London, broken down by type — and the six line items that turn a £45,000 quote into a £52,000 bill.
What Each Type Costs
Most loft conversion companies won't give you a price until someone has been round. That's defensible — the number genuinely depends on your roof — but it leaves you trying to budget a five-figure project with nothing to work from.
So here are the numbers, up front. These are West London ranges for a completed conversion, and they're estimates rather than quotes. What they'll do is tell you whether the project is in the right order of magnitude before you spend a Saturday on surveys.
| Conversion type | Typical West London range | What you get |
|---|---|---|
| Velux / rooflight | £22,000 – £32,000 | One room, existing roof shape unchanged |
| Rear dormer | £42,000 – £62,000 | One large room with full standing height at the back |
| Full-width rear dormer | £48,000 – £68,000 | Maximum width at full height; usually fits a bedroom plus en-suite |
| Hip to gable | £48,000 – £70,000 | Squares off a hipped roof; adds width, not height |
| Hip to gable + rear dormer | £58,000 – £85,000 | The standard package on an inter-war semi |
| L-shaped dormer | £55,000 – £80,000 | Wraps around a terrace's rear outrigger; bedroom plus bathroom |
| Mansard | £65,000 – £105,000 | Effectively a new storey; commonly two rooms |
Adding a bathroom costs roughly £5,000–£9,000 on top of any of these, depending on whether it's a shower room or a full bathroom and how far the soil stack has to move.
For a sanity check against independent sources: Checkatrade puts the average loft conversion in Ealing at just under £36,000 across all types, with most jobs falling between £23,000 and £55,000. Specialists advertising in these postcodes quote from £44,000 upward for a dormer or hip to gable, and one of the larger firms publishes a range of £44,000 to £108,000.
Those figures aren't in conflict. The average is low because it includes rooflight conversions; the specialist ranges are higher because specialists mostly do the bigger types.
What a Quote Normally Includes
- Structural design and calculations
- Scaffolding and site protection
- Steels, new floor structure and roof works
- The dormer, gable or mansard structure itself
- Windows and rooflights
- A permanent staircase
- Insulation to current standards
- Fire safety works — fire doors, fire-resisting floor, interlinked alarms
- Electrics, lighting and heating in the new room
- Plastering, decoration and floor covering
- Building control inspections and sign-off
- Clearing and removing waste
Six Costs Quotes Often Leave Out
This is the part worth reading twice, because it's where budgets slip.
1. VAT
Some quotes are stated plus VAT, some inclusive. On a £50,000 job that's a £10,000 difference, and it's the single most common misunderstanding in the whole process. Ask which it is before you compare anything.
2. Party Wall Surveyor
If your conversion involves a shared wall — which it will on any terrace or semi — you have to serve notice, and if your neighbour dissents, surveyors get appointed and you pay.
3. Planning and Design Fees
If you need planning permission you'll want drawings, and possibly a planning consultant. If you don't, a Lawful Development Certificate is still worth having: it costs half the normal planning fee and it's what proves the work was lawful when you sell.
4. Building Control
A separate consent from planning, required on every loft conversion regardless. Fees vary by authority and by scheme.
5. Bathroom Fit-Out Beyond the Basics
The £5,000–£9,000 range assumes a sensible shower room. Tiling choices, underfloor heating and moving the soil stack all move it.
6. Making Good Downstairs
The staircase has to land somewhere. On most houses that means reworking the landing or taking space from a bedroom, and the redecorating that follows is real work that some quotes exclude.
What Actually Drives Your Number Up or Down
Access. This is the biggest variable people don't anticipate. A semi with a side passage lets materials and waste go straight to the back. A mid-terrace with no side return means every steel beam, every skip load and every pallet of tiles goes through the hallway — slower, more labour, higher price for identical work.
Roof structure. Traditional cut-timber roofs have usable space under the ridge. Modern W-shaped trussed rafters fill the loft with timber that can't simply be cut away — converting one means replacing the structure, and that pushes the cost well beyond a standard conversion.
Existing head height. Plenty of height means a rooflight conversion is on the table. Not enough means a dormer or hip to gable, and the price roughly doubles.
Whether there's a bathroom. Plumbing into a loft is straightforward; it just isn't free.
Conservation area status. More design work, a planning application, and material matching that has to satisfy a conservation officer. Expect both the timeline and the professional fees to be higher.
The staircase. On a wide house it's a detail. On a narrow terrace it can be the thing that dictates the entire layout, and occasionally the thing that makes a conversion unviable.
Working the Other Way: What Your Budget Buys
Most people arrive with a number rather than a conversion type, so here's the same information from that end.
Around £25,000. A rooflight conversion on a loft that already has the height. One room, no bathroom, simple finish, no change to the roof outside. This is the only budget at which a loft conversion in West London is a modest project.
Around £45,000. A rear dormer on a terrace or semi — one large room with full standing height at the back, no bathroom. Or a hip to gable without a dormer on an inter-war semi, which gains width rather than height.
Around £60,000. The combination most people in outer West London end up with: hip to gable plus rear dormer, giving both width and standing height, usually with a shower room. On a terrace, this is roughly where an L-shaped dormer starts.
Around £80,000. An L-shaped dormer with a proper en-suite, or a modest mansard. At this level you're generally buying a bedroom-plus-bathroom that works as a main bedroom rather than a spare.
£100,000 and above. A mansard delivering two rooms and a bathroom, or a large conversion on a period property where conservation requirements drive both the design and the materials.
Add professional fees on top of all of these where planning permission, a party wall surveyor or a structural engineer's separate appointment is involved.
Why London Costs More
A loft conversion in London typically runs 20–35% above the national figure for the same type of work. The reasons are unglamorous: labour rates, the difficulty of getting materials in and waste out on dense streets, parking and permit costs, and a housing stock that is older and more frequently protected than the national average.
Within London, West London sits toward the higher end — not because of the postcode itself, but because so much of the stock is Victorian, Edwardian or in a conservation area. The same conversion on comparable houses genuinely costs more in Richmond or Chiswick than in Northolt or Hayes, and that gap is a consequence of what's being converted rather than of who lives there.
Does a Loft Conversion Add Value?
Usually, and the mechanism is simple: an extra bedroom moves a house into a different search bracket. A three-bed that becomes a four-bed is being looked at by a different set of buyers.
Two honest caveats, though.
The first is that value added is not the same as money back. In a strong market a well-executed conversion in West London can approach or exceed its cost in added value; in a flat market it won't. Nobody can promise you a return, and any company that does is guessing.
The second is that a bedroom without a building regulations completion certificate is not a bedroom as far as a surveyor or a solicitor is concerned. Unsigned-off loft rooms show up in conveyancing constantly and they cost money and time to resolve at exactly the wrong moment. Whatever else you economise on, don't economise on the paperwork.
How to Compare Quotes Properly
Three quotes is the sensible minimum on a job this size, and comparing them means checking that they cover the same thing:
- Is the price inclusive of VAT or plus VAT?
- Does it include building control fees and inspections?
- Does it include the staircase and making good the landing?
- Is insulation specified, and to what standard?
- Are fire doors and interlinked alarms in the price?
- Who serves the party wall notices, and who pays for a surveyor if one is needed?
- What's the payment schedule, and what's the retention at the end?
Cost Questions
Can you do a loft conversion for £20,000?
Occasionally — a rooflight conversion, on a loft that already has the height, with no bathroom and a simple finish. Not for a dormer or hip to gable in West London.
What's the cheapest type of loft conversion?
A Velux or rooflight conversion, because the roof structure doesn't change and there's no external building work.
How much does a loft conversion cost in Ealing specifically?
Checkatrade's Ealing average is just under £36,000 across all types. Most dormer and hip-to-gable conversions in the borough land between £42,000 and £70,000.
Do I pay in stages?
Almost always. A deposit, then payments at agreed stages, with a final balance on completion and sign-off. Be cautious about large sums up front.