How much does a loft conversion cost in 2026?
Loft conversion prices by type for 2026, including VAT, with London figures, the fees and extras a builder's quote leaves out, and when planning permission applies.
A loft conversion costs £30,000 to £96,000 in 2026, including VAT, and the type your roof can take sets most of that price. We give prices for the four main types of loft conversion and three variants, what London adds, the fees and extras a builder's quote leaves out, and when you need planning permission and building regulations approval.
Loft conversion cost by type
These are 2026 prices for the conversion itself, including VAT at 20%. The staircase, the steelwork for the new floor, any en suite and the professional fees usually sit outside them, and we price each of those further down.
| Type | UK | London | What changes on the roof |
|---|---|---|---|
| Rooflight (velux) | £30,000 – £48,000 | £35,000 – £56,000 | Windows go into the existing slope; the roof keeps its shape |
| Dormer | £42,000 – £72,000 | £49,000 – £84,000 | A box with vertical walls built out from the rear slope |
| Hip to gable | £54,000 – £78,000 | £63,000 – £91,000 | The sloping side of the roof is rebuilt as a vertical gable wall |
| L-shaped dormer | £60,000 – £90,000 | £70,000 – £105,000 | Two joined dormers, over the main roof and the rear outrigger |
| Modular | £54,000 – £84,000 | £63,000 – £98,000 | The roof room is built off site, then installed |
| Mansard | £66,000 – £96,000+ | £77,000 – £112,000+ | The rear slope is rebuilt almost vertical under a flat top |
| Piggyback | £72,000 – £108,000 | £84,000 – £126,000 | The whole roof is lifted to create height |
No official body publishes what a loft conversion costs, so these ranges are market rates rather than a measured average. Every loft moves within its range once the head height, the roof structure and the staircase position are known.
Velux (rooflight) conversion cost
A rooflight conversion costs £30,000 to £48,000 including VAT. Often called a velux conversion after the roof window brand, it leaves the roof's shape alone: windows go into the existing slope and the work happens inside. It is the cheapest route and usually needs no planning application, but it only works where the loft already has the head height.
Dormer loft conversion cost
A dormer costs £42,000 to £72,000 including VAT. A dormer conversion builds a box out from the rear slope with vertical walls, usually under a flat roof, which turns sloping ceiling into full-height floor space. Most rear dormers in England fall within permitted development, so they need no planning application.
Hip to gable loft conversion cost
A hip to gable costs £54,000 to £78,000 including VAT. A hip to gable conversion rebuilds the sloping side of a hipped roof as a vertical gable wall, so it suits semi-detached, end-of-terrace and detached houses. It is often combined with a rear dormer, and the extra roof work and steel put it above a dormer alone.
Mansard loft conversion cost
A mansard costs £66,000 to £96,000 or more including VAT. A mansard conversion rebuilds the rear slope at a near-vertical angle under a flat top, which gives the most room of the four. It changes the roof's profile, so it needs a planning application, and it is one of only two routes left when the loft is too low for anything else.
L-shaped, modular and piggyback conversions
An L-shaped dormer runs over the main roof and a rear outrigger and costs £60,000 to £90,000 including VAT. Where its two rooflines meet they form a valley, the most common leak point on a badly built conversion. A modular conversion, built off site and then installed, costs £54,000 to £84,000.
A piggyback lifts the whole roof to create height and costs £72,000 to £108,000, the dearest route of all. Like a mansard, it needs a planning application.
Can your loft be converted?
Two facts about the house decide which row of that table applies before any design choice does: the height under the ridge and the way the roof was built. Neither is a specification you can pick.
Measure from the top of a ceiling joist to the underside of the ridge. About 2.2 to 2.4 metres is the working minimum, because the new floor, insulation and plasterboard take 250 to 400 millimetres out of it. Below that, the options are a mansard or a piggyback, at the top of the price table.
| Check | Straightforward | Dearer or ruled out |
|---|---|---|
| Height, ceiling joist to ridge | 2.2 – 2.4 m or more | Less: a mansard or piggyback only |
| Roof pitch | About 30 degrees or steeper | Shallower: too little volume to use |
| Roof structure | Cut roof, usual before about 1965 | Trussed rafters: £5,000 – £15,000 more |
| Roof shape | Pitched | Flat: cannot be converted |
Houses built before about 1965 usually have a cut roof, assembled on site from individual timbers, which leaves an open triangle that converts easily. Almost every house from the mid-1970s on has trussed rafters, braced by W-shaped webs that cannot simply be cut out. Converting one means new steel at wall plate level and a new floor hung from it, which adds £5,000 to £15,000.
What a loft conversion quote leaves out
A loft quote usually prices the conversion. These lines often sit outside it:
- VAT at 20%, unless the quote says it is included.
- The staircase: £3,000 to £10,000, depending on where it lands and how much of the room below it takes.
- Steelwork and the new floor structure: £2,000 to £5,000 on a cut roof, and considerably more on trussed rafters.
- An en suite: £5,000 to £12,000, and more where the soil stack has to be extended.
- Electrics for the new room: £1,500 to £3,000 for the first fix and sockets.
- Contingency: 10 to 15% of the build, held back for what the roof reveals once it is opened.
Older roofs hide the surprises, because the conversion opens up a part of the house few owners have looked at closely in decades. That is what the contingency is for.
Loft conversion fees: drawings, engineer, building control and planning
Every conversion carries professional and council fees on top of the build. Planning fees in England are set nationally; the rest are quoted.
| Fee | Typical cost | When it applies |
|---|---|---|
| Architectural drawings | £1,200 – £2,500 | Every conversion |
| Structural engineer's calculations | £395 – £1,200 | Every conversion, rooflight at the low end and mansard at the top |
| Building control | £700 – £1,400 | Every conversion, with a dormer in a dearer bracket |
| Party wall surveyor | £1,200 – £3,000 per agreement | Structural work to a shared wall, unless the neighbour consents in writing |
| Householder planning application | £548 | Mansards, piggybacks and anything outside permitted development |
| Lawful Development Certificate | £274 | Optional proof that a permitted development loft is lawful |
Every loft conversion needs a structural engineer's calculations for the new floor and steels. The fee follows the structure: £395 to £600 for a rooflight conversion, £450 to £700 for a rear dormer, £600 to £1,100 for a hip to gable and £700 to £1,200 for a mansard.
Most councils price a loft conversion as its own building control category, and a dormer moves it into a dearer bracket. Tower Hamlets charges £951.79 without a dormer and £1,363.10 with one, while Camden charges £1,406.33 and Islington £1,782.
In England and Wales, you have to tell your neighbours before building work on or near a shared wall, and a loft on a terrace or semi usually means structural work to one. The neighbours on each side get a party wall notice, and a surveyor's award costs £1,200 to £3,000 per agreement, or nothing where a neighbour consents in writing.
VAT on a loft conversion
A loft conversion in a lived-in home carries VAT at 20% on both labour and materials, and no relief applies. On a £50,000 quote that leaves VAT out, the bill is £60,000.
The reduced 5% rate covers two nearby cases: renovating a home that has stood empty for 2 years or more, and work that changes the number of dwellings. A loft turned into a separate self-contained flat can fall into the second case. A new bedroom in an occupied house falls into neither.
Loft conversion costs in London and across the UK
A dormer in London costs £49,000 to £84,000 including VAT, against £42,000 to £72,000 across the UK. Measured tender prices put inner London about 17% above the UK average.
Per square metre, a London loft with rooflights only starts at about £1,900 and one with a dormer at about £2,400, before VAT and fees. A larger London house with several bedrooms and bathrooms in the roof can pass £100,000.
Scotland, Wales, the North West and Yorkshire sit at the bottom of the UK range for a rear dormer, with the Midlands, the South West and the East of England in between.
On a terraced street, a loft carries costs a detached house avoids. Scaffolding and materials come in from the pavement or through the house, there is a neighbour on one side or both, and a rear outrigger adds the valley an L-shaped dormer has to seal.
Planning permission for a loft conversion
In England, most rooflight and rear dormer conversions need no planning application, because they count as permitted development. The permitted development limits for a loft are:
- No more than 40 cubic metres of added roof space on a terraced house, or 50 cubic metres on a semi-detached or detached house.
- Nothing higher than the existing roof, and nothing beyond the roof slope on the front of the house where it faces a road.
- Materials similar in appearance to the existing house.
- No verandas, balconies or raised platforms.
- Side-facing windows obscure-glazed, with any opening part at least 1.7 metres above the floor.
- The new roof set back at least 20 centimetres from the original eaves, where practicable.
- The house is not a flat, is not on designated land such as a conservation area, and has not already had storeys added under permitted development.
A mansard or a piggyback changes the roof's profile and needs an application, as does any conversion outside those limits or on a listed building. Where you need planning permission for a loft conversion, the householder fee in England is £548.
Where the work fits the limits, a £274 Lawful Development Certificate confirms it is lawful before you build. It is optional.
Wales, Scotland and Northern Ireland
The limits above are England's. Welsh permitted development rights differ, Scotland issues a building warrant rather than building regulations approval, and Northern Ireland runs its own planning and building control. The party wall process covers England and Wales only, and Scotland has different rules.
Building regulations for a loft conversion
Building regulations approval is needed for every loft conversion, including one built under permitted development. Building control checks the structure under Part A, fire safety and escape under Part B, the staircase under Part K and insulation under Part L.
For the staircase, Approved Document K asks for 2 metres of headroom over the stairs, relaxed for a loft to 1.9 metres at the centre and 1.8 metres at the side. A stair that cannot reach that leaves you with a loft room rather than a bedroom, and a buyer will value it as one.
How long a loft conversion takes
Time on site runs from 4 weeks for a small rooflight conversion to 14 weeks for a hip to gable, with mansards and piggybacks at the long end.
| Type | Time on site |
|---|---|
| Rooflight (velux) | 4 – 6 weeks |
| Rear dormer | 6 – 10 weeks |
| Hip to gable | 10 – 14 weeks |
Before the builder starts, allow 2 to 3 months for design, surveys and approvals. The structural calculations take about 5 to 7 working days once the drawings exist, and a full planning application adds about 8 weeks from validation.
Does a loft conversion add value?
Nationwide's house price research, based on its own mortgage lending, found that 10% more floor space adds around 5% to a home's price. An extra double bedroom on a two-bedroom house adds around 13%, and an extension that adds a bedroom and a bathroom adds up to 24%, which is what a loft with an en suite delivers.
The uplift is capped by the ceiling price for your street. On a terrace, a loft is often the only way to add a bedroom without losing garden.
A loft conversion is the wrong spend when:
- The loft is under about 2.2 metres to the ridge, so the only routes are a mansard or a piggyback from £66,000 including VAT.
- House prices on the street already sit at the ceiling, so the conversion costs more than it adds.
Common questions
How much does a loft conversion cost in the UK?
A loft conversion costs £30,000 to £96,000 including VAT in 2026, depending on type. A rooflight conversion costs £30,000 to £48,000, a dormer £42,000 to £72,000, a hip to gable £54,000 to £78,000 and a mansard £66,000 or more. The staircase, fees and any en suite usually come on top.
Can you do a loft conversion for £10k?
No, £10,000 does not pay for a habitable loft room in 2026. The cheapest conversion, with rooflights in the existing slope, starts at about £30,000 including VAT. A staircase and the building control fee alone come to £3,700 to £11,400.
What is the cheapest way to convert a loft?
A rooflight conversion is the cheapest way to convert a loft, at £30,000 to £48,000 including VAT, because the roof keeps its shape and it usually needs no planning application. It only works where the loft already has about 2.2 to 2.4 metres from ceiling joist to ridge. A lower loft needs one of the dearer types.
Does converting a loft add value?
A loft conversion usually adds value, and most when it creates a double bedroom with its own bathroom. Nationwide's research puts an extra double bedroom on a two-bedroom house at around 13% of the price, and a bedroom plus a bathroom at up to 24%. The uplift stops at the ceiling price for your street.
What is the 10 year rule for loft conversion?
In England, a council cannot take planning enforcement action against building work done without permission once 10 years have passed since it was substantially completed. The limit is set by section 171B of the Town and Country Planning Act 1990, took effect on 25 April 2024 with transitional rules for earlier work, and is 4 years in Wales. It does not cover building regulations, so a missing completion certificate still matters when you sell.
How much does a loft conversion cost per m2?
In London, a loft conversion starts at about £1,900 per square metre with rooflights only and about £2,400 per square metre with a dormer, before VAT and fees. A small loft costs more per square metre than a large one, because the staircase and the fees do not shrink with it.
How much does a loft conversion cost in London?
Including VAT, a loft conversion in London costs £35,000 to £56,000 with rooflights, £49,000 to £84,000 with a dormer and £77,000 to £112,000 or more as a mansard. London sits about 17% above the UK average. Fees, the staircase and any en suite come on top.
Is a loft extension the same as a loft conversion?
A loft extension is a loft conversion that adds volume to the roof, such as a dormer, hip to gable or mansard, and it is priced the same way. An attic conversion is the same job under another name. A rooflight conversion is the one type that adds no volume, because the roof keeps its shape.
Do you pay VAT on a loft conversion?
A loft conversion in an occupied home carries VAT at 20% on labour and materials. The reduced 5% rate applies only to renovating a home empty for 2 years or more, or to work that changes the number of dwellings, such as creating a self-contained flat. Check whether each quote includes VAT before comparing them.