A loft conversion is one of the smartest ways to add space to your home without eating into your garden or dealing with the hassle of foundations. But the cost varies massively depending on what type you go for, and a lot of people get stung because they did not understand the differences before getting quotes.
Here is what loft conversions actually cost in 2026, broken down by type, with the extras that most guides forget to mention.
A loft conversion in the UK costs £15,000 to £75,000+ depending on the type. A Velux (rooflight) conversion starts at £15,000. A dormer runs £35,000 to £60,000. A hip to gable costs £45,000 to £65,000. A mansard is £50,000 to £75,000+. Most homeowners spend around £40,000 to £55,000.
Loft Conversion Costs by Type
The type of conversion is the biggest factor in the price. Here is what each one involves and what it costs.
Velux (Rooflight) Conversion: £15,000 to £30,000
This is the simplest and cheapest option. Velux windows are fitted into the existing roof slope, the floor is strengthened, a staircase is added, and the space is insulated and plastered. The roofline stays exactly as it is.
It works well if your loft already has decent headroom (at least 2.4 metres at the ridge). If it does not, this type will not solve the problem because you are not changing the roof shape at all.
| Spec Level | Cost | What's Included |
|---|---|---|
| Budget | £15,000 to £20,000 | 2 Velux windows, basic staircase, standard electrics, plastered and painted |
| Mid range | £20,000 to £25,000 | 3 to 4 Velux windows, better staircase, spotlights, carpet |
| Premium | £25,000 to £30,000 | Large or Juliet balcony windows, oak staircase, USB sockets, en suite plumbing prep |
Dormer Conversion: £35,000 to £60,000
A dormer extends out from the rear of the roof to create a flat roofed box with vertical walls. This gives you full standing headroom across a much larger area than a Velux conversion. It is the most popular type in the UK and is what most people picture when they think "loft conversion".
A rear dormer on a typical semi detached house creates roughly 15 to 25 m2 of usable space, which is enough for a double bedroom with an en suite.
| Spec Level | Cost | What's Included |
|---|---|---|
| Budget | £35,000 to £42,000 | Flat roof dormer, standard windows, basic bathroom suite, standard staircase |
| Mid range | £42,000 to £52,000 | Full width dormer, better windows, mid range en suite, engineered oak staircase |
| Premium | £52,000 to £60,000 | Full width dormer, large format windows, walk in shower, underfloor heating, bespoke joinery |
Hip to Gable Conversion: £45,000 to £65,000
If you have a hip roof (where the side of the roof slopes inwards rather than having a vertical gable wall), this conversion extends that sloping side outwards to create a vertical wall. This is very common on 1930s semi detached houses and gives you significantly more floor space than a dormer alone.
Many hip to gable conversions include a rear dormer as well, which maximises the usable area. If you are doing both, expect to pay £55,000 to £70,000.
| Spec Level | Cost | What's Included |
|---|---|---|
| Budget | £45,000 to £52,000 | Hip to gable with small dormer, basic en suite, standard finish |
| Mid range | £52,000 to £60,000 | Hip to gable with full rear dormer, mid range en suite, good quality staircase |
| Premium | £60,000 to £65,000+ | Hip to gable with full dormer, premium en suite, underfloor heating, bespoke storage |
Mansard Conversion: £50,000 to £75,000+
A mansard alters the entire roof structure to create near vertical walls (set at a minimum 72 degree angle) with a flat roof on top. This gives you the maximum possible space but it is the most disruptive, the most expensive, and almost always requires planning permission.
Mansards are most common in London and conservation areas where maximising every square foot of space justifies the higher cost and planning headache. In London specifically, expect to pay £65,000 to £100,000+ for a mansard.
| Spec Level | Cost | What's Included |
|---|---|---|
| Budget | £50,000 to £58,000 | Standard mansard, basic finish, standard en suite |
| Mid range | £58,000 to £68,000 | Full mansard with dormer windows, mid range bathroom, good quality finish |
| Premium | £68,000 to £75,000+ | Full mansard, premium bathroom, Juliet balcony, bespoke joinery, underfloor heating |
Cost per Square Metre
If you want to compare like for like, here is what each type costs per square metre:
| Type | Cost per m2 |
|---|---|
| Velux | £1,100 to £1,600 |
| Dormer | £1,500 to £2,000 |
| Hip to gable | £1,400 to £2,000 |
| Mansard | £1,900 to £2,600 |
Extra Costs to Factor In
The headline prices above cover the conversion itself. But there are a few things that can push the total higher:
| Extra | Typical Cost |
|---|---|
| En suite bathroom | £3,000 to £7,000 |
| Architect / drawings | £1,000 to £3,000 |
| Structural engineer | £400 to £1,000 |
| Building regulations | £500 to £1,000 |
| Planning application (if needed) | £258 |
| Party Wall surveyor (if applicable) | £1,000 to £2,500 per neighbour |
| Scaffolding | £800 to £1,500 |
| Skip hire | £250 to £400 |
Most loft conversion companies include scaffolding and skip hire in their price, but always check. Architect fees, structural engineer fees and building regs are almost always on top.
Planning Permission and Building Regs
Planning Permission
Most loft conversions fall under permitted development, which means no planning permission needed. The rules are:
- No more than 40 cubic metres of additional space for terraced houses, or 50 cubic metres for detached and semi detached
- No extension beyond the existing roof plane facing a highway
- Materials must match the existing house
- The highest point must not exceed the existing roof height
- Side facing windows must be obscure glazed and non opening below 1.7 metres
If you live in a conservation area, your home is a listed building, or you are doing a mansard conversion, you will almost certainly need planning permission. The application fee in England is £258 and decisions typically take 8 weeks.
Building Regulations
Building regulations approval is always required, no exceptions. This covers structural safety, fire protection (you will need a fire door and possibly a mains powered smoke alarm system), insulation standards, staircase design and electrical safety. Budget £500 to £1,000 for building control fees. Your loft conversion company should handle the submissions but make sure this is in their quote.
How Long Does It Take?
| Phase | Timeline |
|---|---|
| Design and drawings | 2 to 4 weeks |
| Structural calculations | 1 to 2 weeks |
| Building regs submission | 4 to 8 weeks |
| Planning application (if needed) | 8 to 12 weeks |
| Party Wall notice (if needed) | 8 weeks minimum |
| Velux build | 3 to 4 weeks |
| Dormer build | 5 to 7 weeks |
| Hip to gable build | 7 to 9 weeks |
| Mansard build | 8 to 10 weeks |
From first phone call to moving furniture in, expect 4 to 6 months for a straightforward dormer, and 6 to 9 months if planning permission is involved.
How to Save Money on a Loft Conversion
- Choose Velux if you have the headroom. If your loft already has 2.4 metres at the ridge, a Velux conversion gives you a usable room for half the cost of a dormer.
- Skip the en suite. An en suite adds £3,000 to £7,000. If the family bathroom is just below on the landing, you probably do not need one.
- Standard staircase. A basic softwood staircase costs £800 to £1,500. An oak or bespoke staircase costs £3,000 to £6,000. Unless the staircase is a design feature, go standard.
- Get three quotes. Prices for loft conversions vary by 20% to 30% between companies for the same spec. Always compare.
- Do your own decorating. Painting and carpeting after the builders leave saves you £500 to £1,000.
Is It Worth It?
Almost always, yes. A loft conversion typically adds 15% to 20% to your property value. On a £300,000 house, that is £45,000 to £60,000 of added value for a conversion that might cost £40,000 to £55,000. It is one of the few home renovation projects where you are likely to get your money back and then some.
If you are weighing up a loft conversion against a house extension, the loft is usually cheaper per square metre and less disruptive because the builders are working above you rather than digging up your garden.
You will also need a plumber if you are adding an en suite, and the overall project ties into your wider bathroom renovation budget.
A loft conversion costs £15,000 to £75,000+ in the UK depending on the type. Most people opt for a dormer at £40,000 to £55,000 and end up with a new bedroom and en suite that adds real value to their home. Get three quotes, check whether you need planning permission, and make sure building regulations are included in the price. It is one of the best investments you can make in your property.
Frequently Asked Questions
What is the cheapest type of loft conversion?
A Velux (rooflight) conversion is the cheapest option at £15,000 to £30,000. It works by adding windows to your existing roof without changing the roofline. This only works if your loft already has enough headroom, which typically means a ridge height of at least 2.4 metres.
Do I need planning permission for a loft conversion?
Most loft conversions fall under permitted development and do not need planning permission, provided you stay within the limits: 40 cubic metres of additional space for terraced houses or 50 cubic metres for detached and semi detached houses, materials that match the existing house, no extension beyond the existing roof plane facing a highway, and the highest point does not exceed the existing roof. If your property is in a conservation area, is a listed building, or you are building a mansard, you will almost certainly need planning permission. Building regulations approval is always required regardless.
How long does a loft conversion take?
A Velux conversion takes 3 to 4 weeks on site. A dormer takes 5 to 7 weeks. A hip to gable or mansard takes 7 to 10 weeks. Add 2 to 4 months before building starts for design, structural calculations, building regulations approval and any planning applications.
Does a loft conversion add value to a house?
Yes. A well done loft conversion typically adds 15% to 20% to a property's value. On a £300,000 house, that is £45,000 to £60,000 of added value. Adding an en suite bathroom increases the value further. The return is usually better than the cost of the conversion itself, making it one of the best investments you can make in your home.
Can I convert my loft if it has a low roof?
You need a minimum of 2.2 metres of headroom at the highest point for a usable conversion, though 2.4 metres is preferred. If your existing roof is too low, a dormer, hip to gable or mansard conversion can create additional height. A Velux conversion will not help with low headroom since it uses the existing roof structure as it is.