Loft Conversion Cost in Bromley and London: 2026 Price Guide

Loft Conversion Costs in Bromley at a Glance

These are the local figures this site uses throughout. The guide below sets out the national ranges they are built on, and why London and the South East run above them.

Most people start looking into a loft conversion cost and hit a wall of forms. You want a number. You get a quote request. So here is the number first, before anything else. In 2026 a normal loft conversion in the UK runs between £45,000 and £80,000. The cheapest type starts near £20,000. The biggest jobs on larger London houses reach £90,000. Where you land inside that spread has less to do with the size of your loft than with the shape of your roof.

What Changed in Loft Conversion Cost in 2026

Two things moved this year, and both matter if you are pricing a job now.

The gap between regions got wider. National guides now quote one average and then a separate London figure, because the two have pulled apart. One 2026 dataset puts a standard dormer at £40,500 in London, well above the figures used elsewhere in the country. If you are in Bromley, north-west Kent or south-east London, the national average is a floor rather than a middle.

The second shift is in how prices get quoted. More firms now publish a rate per square metre. It sounds helpful. It is often misleading, and there is a section below on why.

Modular loft conversions also became easier to price this year, at around £45,000. They suit a narrow set of houses, so treat that as a side note rather than a benchmark.

Loft Conversion Cost by Type in 2026

The type of conversion drives the price more than floor area does. Here are the 2026 averages.

• Velux or rooflight conversion: around £27,500. Nothing structural happens to the roof. Basic schemes start near £20,000.
• Dormer conversion: around £50,000. A standard 2026 dormer with a bathroom runs £55,000 to £65,000.
• Hip-to-gable conversion: around £60,000. With a rear dormer added, the total reaches £80,000.
• Mansard conversion: around £65,000. Larger mansards reach £90,000.

The spread between the cheapest and the dearest is more than threefold. That is not a difference in quality. It is a difference in how much of your roof comes off and goes back on.

A Velux conversion touches the roof only where the windows go. A mansard rebuilds most of it. Everything else sits between those two points.

One figure worth holding onto: the dormer itself, as a build element, costs £8,000 to £18,000. Rooflights cost £1,500 to £4,000. So the jump from a rooflight job to a dormer job is not a small upgrade. It is a different build.

Loft Conversion Cost by Property Type

Here is the part most cost guides skip. You do not pick your conversion type. Your roof picks it for you. So the useful question starts with the house.

• Victorian or Edwardian terrace with a rear back addition. The back addition, sometimes called an outrigger, lets you build an L-shaped dormer. Budget £60,000 to £90,000. You get a bedroom and an en-suite rather than one room.
• Terrace with no back addition. A plain rear dormer. Budget £45,000 to £65,000.
• Semi-detached house with a sloping side roof. A hip-to-gable, usually with a rear dormer. Budget £55,000 to £80,000.
• Detached house. A dormer or a hip-to-gable, sometimes on both sides. Budget £55,000 to £90,000.
• Bungalow. The whole roof is available, so this is closer to adding a floor. Budget £50,000 to £85,000.
• Larger period house. A mansard, where the proportions carry it. Budget from £65,000.
• Flat or maisonette. Usually not possible. The roof space is rarely yours to convert.

That last line is not a dodge. In a leasehold flat the loft normally belongs to the freeholder. Sorting that out comes before any builder quotes.

What Pushes a Loft Conversion Cost Up

Two quotes on the same street can differ by £20,000. These are the reasons, roughly in order of how much they move the number.

Head height you start with. The single biggest factor. Enough height means you buy a floor, insulation, windows and a staircase. Not enough means you buy a rebuilt roof. Those are different jobs at different prices.

Roof structure. Older roofs were cut on site, rafter by rafter, and usually leave a usable void. Many postwar roofs use W-shaped trussed rafters that fill the space with timber. Trusses can come out, but that is structural work and it shows in the price.

Steel beams. Almost every conversion needs them, so the new floor carries itself rather than resting on your ceiling. How many, how big, and how hard they are to get into the house all matter. On a terrace with no side access they sometimes come in through the roof.

Where the staircase goes. People underrate this. Stairs need somewhere sensible to land, with proper headroom above them. Sometimes that costs you part of a bedroom below. It is a design problem before it is a money problem.

An en-suite. A bathroom in a loft means drainage, which means either a pump or a long run down through the house. Budget several thousand pounds.

Access and scaffolding. A detached house with a drive is cheaper to work on than a mid-terrace on a busy road.

The Costs Most Quotes Leave Out

A cheap quote is often just a shorter quote. Ask about all of these before you compare anything.

• Structural engineer: £1,500 to £3,500. Someone has to size the steels. This is not optional.
• Scaffolding: £2,000 to £5,000. One 2026 source puts a full scaffold at £4,750, and that excluded a temporary roof.
• Planning application, where you need one. Not every job does, but conservation areas normally do.
• Building control fees. Every loft conversion needs sign-off, whether or not it needs planning permission.
• Party wall surveyor. If you share a wall, assume you need one.
• Decorating, flooring and blinds. Very often excluded.

Together these commonly add ten to twenty per cent. One quote at £55,000. Another at £62,000. They can describe exactly the same build. One of them just told you the whole price.

Why Loft Conversion Cost Per Square Metre Misleads

Rates per square metre look like a fair way to compare firms. They are not, for two reasons.

Small lofts distort the figure. Fixed costs like scaffolding, steels and the staircase do not shrink when the room does. Spread those over 15 square metres instead of 30 and the rate roughly doubles.

The small loft then looks expensive. It is not. It is just small.

Roof shape distorts it too. A cut roof and a trussed roof of the same floor area need different amounts of work. The rate hides that. Two quotes with the same rate per square metre can be pricing two different builds.

Use the total price. Then ask what is inside it.

How to Compare Three Loft Conversion Quotes

Three questions do most of the work.

Ask whether the structural engineer is in the price, and who hires them. A vague answer means the quote is not finished.

Ask what they assumed about the roof structure. If nobody went up into the loft, the price is a guess. A firm that looked and says "cut roof, no trusses" is quoting something real.

Ask what the stage payments are tied to. Payments against finished work are normal. Large sums up front are not.

Take three quotes. On a build costing more than a car, that is not being awkward. It is the obvious thing to do, and most people do it.

Is a Loft Conversion Cheaper Than Moving in 2026

For most families in Bromley and south-east London, yes.

A typical conversion here runs £45,000 to £80,000. There is no stamp duty on it, no agent fee, and no moving cost. You keep your road, your neighbours and your school run.

Moving up a bedroom means paying the price gap between a three-bed and a four-bed, plus stamp duty, plus legal fees, plus removals. In areas where that gap is wide, the loft wins on money alone.

It stops winning when the house has problems a loft will not fix. A small garden stays small. A bad layout downstairs stays bad. Converting the roof buys you rooms, not a different house.

FAQ

How much does a loft conversion cost on average? Around £50,000. That is the UK figure for 2026, and the normal range runs £45,000 to £80,000. A Velux conversion sits near £27,500 and a mansard near £65,000. London and the South East run above the national figure, so treat the average as a starting point rather than a likely price.

Can you do a loft conversion for £20,000? Only at the very bottom of the market, and not in London. Velux-only schemes start near £20,000. In Bromley the realistic entry point is higher. A much cheaper quote usually leaves out the staircase, the insulation or the building control sign-off, so check what is inside it.

How much does a dormer loft conversion cost? Around £50,000 on average in 2026, rising to £55,000 to £65,000 for a standard job with a bathroom. The dormer structure itself accounts for £8,000 to £18,000. A dormer added to a hip-to-gable conversion pushes the total towards £80,000.

Is a loft conversion more expensive in London? Yes. Labour and materials cost more, access is harder, and scaffolding on a terraced street adds work. One 2026 dataset puts a standard dormer at £40,500 in London. For Bromley, north-west Kent and south-east London, budget above the national average rather than at it.

What is the cheapest type of loft conversion? A Velux or rooflight conversion, at around £27,500. Nothing structural happens to the roof, so there is far less work involved. It is only an option if your loft already has enough height. If it does not, the cheapest real option becomes a dormer at about £50,000.

Verdict on Loft Conversion Cost

For a normal job in 2026, budget £45,000 to £80,000, and expect the upper half of that in London or the South East. If your loft already has the height, ask about a rooflight conversion first. It costs around £27,500. That buys the same bedroom a dormer buys for about £50,000.

The single biggest saving available is not haggling. A loft conversion cost is settled at the start, when the type gets chosen, not at the end when you argue over the total. A firm that goes up into your loft before pricing will tell you more in ten minutes than any online calculator, including this guide.

Then get three quotes, and check that all three include the engineer, the scaffold and the building control fees. That one check is worth more than most negotiation.