Types of Loft Conversion in 2026: Which One Suits Your House

Most people pick a loft conversion the wrong way round. They read about a dormer, decide they want one, then ask builders to price it. Then two firms say the roof will not take it, and the whole thing stalls. The types of loft conversion available to you are set by the roof you already have. Work that out first and the price, the planning position and the timeline all fall into place behind it. This guide covers all five, what each suits, and the lofts that cannot be converted at all.

What Changed for Loft Conversion Types in 2026

One shift is worth knowing about, because it affects a lot of terraced houses.

The L-shaped dormer used to sit in the footnotes of most guides. In 2026 it gets its own section almost everywhere, and that reflects where the demand is. Victorian and Edwardian terraces with a rear back addition are the dominant house type across large parts of London and the older northern cities. The L-shaped dormer is the conversion built specifically for them, and it produces a bedroom with an en-suite rather than a single room.

The other quiet shift is in how the cheapest option gets described. Rooflight conversions were once treated as the budget compromise. Now they are presented as the right answer for any loft that already has the height, which is a fairer way to put it.

The Five Main Types of Loft Conversion

Cheapest first. These are 2026 starting prices.

• Velux or rooflight conversion, from £20,000. No alteration to the roof shape.
• Dormer conversion, from £30,000. A box built out from the rear roof slope.
• Hip-to-gable conversion, from £35,000. A sloping side roof rebuilt as a vertical wall.
• L-shaped dormer, from £45,000. Two dormers joined over a rear back addition.
• Mansard conversion, from £45,000. The roof rebuilt to near-vertical, rising to £60,000.

Notice the spread. The dearest is three times the cheapest. That gap is not about quality of finish. It is about how much of your roof has to come off.

Adding a dormer to a hip-to-gable pushes that job to £45,000, which puts it level with an L-shaped dormer. Most semis end up here.

Velux and Rooflight Conversions

The cheapest of the types of loft conversion, and the one people skip past too quickly.

Nothing structural happens to the roof. The floor gets strengthened, the space gets insulated and plastered, a staircase goes in, and roof windows are cut in flush with the tiles. From the pavement, the house looks unchanged.

It works on one condition: the loft already has enough height to stand up in across a useful width. If it does, you are buying a bedroom for £20,000. With a dormer on it, that same room costs £30,000. If it does not, this type simply is not available and no amount of wanting it helps.

There is a planning advantage too. Because the roof shape does not alter, rooflight work often stays inside permitted development in places where a dormer would need a full application.

Dormer Conversions

A dormer is a box built out from the rear roof slope, with a vertical face and a flat roof. It starts at £30,000.

It is the most efficient conversion there is. Every square metre of dormer is a square metre of full-height floor, so it buys more usable room per pound than anything else on this list. On a mid-terrace with no side roof slope, it is usually the only option.

The trade is that it is not subtle. That is why dormers go on the back of the house, where the street cannot see them.

Flat roof or pitched roof is the common question. A full-width flat-roofed dormer gives the most space. A smaller pitched one looks better and sometimes makes a planning application easier. On a rear elevation nobody can see, the flat roof normally wins.

Hip-to-Gable Conversions

If your roof slopes on the side as well as the front and back, that side slope is called a hip. It is the reason the loft feels so tight. It cuts the floor area to a narrow strip and puts the low point where you most want to stand.

A hip-to-gable conversion rebuilds that slope as a vertical gable wall, in brick or hung tile to match the house. It starts at £35,000. The room underneath gains real width, which is often the difference between a box room and a proper double bedroom.

It needs a side roof slope, so it is for semi-detached and end-terrace houses. Mid-terraces cannot have one.

Most people pair it with a rear dormer, which takes the job to £45,000. The gable gives you width. The dormer gives you head height across the back. That combination is the standard interwar semi conversion.

L-Shaped Dormer Conversions

Look at the back of your house from the garden. If there is a two-storey section projecting into the garden, that is a rear back addition, sometimes called an outrigger. It is what makes this conversion possible.

An L-shaped dormer builds one dormer on the main rear roof and a second along the back addition, joined where they meet. Seen from above they form an L. It starts at £45,000.

The reason it matters is simple arithmetic. A plain dormer on one of these houses gives you a bedroom. An L-shaped dormer gives you a bedroom and an en-suite. On a three-bedroom Victorian terrace, that is the difference between a loft room and a real extra floor.

The junction where the two dormers meet is the part that separates good work from cheap work. It is a fiddly weathering detail and it is the first place this type leaks. Ask any firm quoting to show you a finished one.

Mansard Conversions

A mansard rebuilds the roof so the rear wall rises at around 72 degrees, almost vertical, under a shallow roof. It runs from £45,000, rising to £60,000.

The result does not feel like a loft conversion. It feels like a floor of the house, because that is effectively what it is. Of all the types of loft conversion, it is the only one that reliably produces two rooms rather than one.

It is also the most disruptive and the most likely to need planning permission. Mansards alter the roof profile substantially, which is hard to keep inside permitted development rules. They cluster on larger period houses where the proportions carry the alteration.

If you are weighing a mansard, get the planning position settled before paying for detailed drawings.

Which Types of Loft Conversion Suit Which House

Match the roof to the type before you price anything.

• Mid-terrace with no back addition. Dormer, from £30,000.
• Victorian or Edwardian terrace with a rear back addition. L-shaped dormer, from £45,000.
• Semi-detached with a hipped side roof. Hip-to-gable, from £35,000, or with a dormer at £45,000.
• Detached house. Dormer or hip-to-gable, sometimes on both sides.
• Bungalow. The whole roof is available, so the limit is where the stairs go rather than head height.
• Larger period house. Mansard, from £45,000.
• Any house with a tall existing loft. Rooflight conversion, from £20,000.

What Type of Loft Cannot be Converted

This is the section most guides leave out, and it is the one that saves people money.

Not enough height. The most common reason. Worth being accurate here, because the internet is not. There is no minimum loft head height written into the building regulations. The figure people quote as a rule is an industry yardstick, not law. What the regulations actually set is headroom over the staircase.

Trussed rafters. Many postwar houses were built with W-shaped trusses that fill the loft with structural timber. They can be taken out and replaced, but that is real structural work and it moves the job into a different price band.

Nowhere for a staircase. A conversion needs compliant stairs and a protected escape route. On some plans there is simply nowhere to put them without losing a room below, which cancels out the gain.

A shallow roof pitch. Very little usable volume, so dormers become the only route and the cost climbs.

Leasehold flats and maisonettes. The roof space usually belongs to the freeholder. That is a legal question and it comes before any building question.

A surveyor who goes up into the loft can rule most of these in or out in about ten minutes. If a firm quotes without going up there, treat the number as a guess.

FAQ

What are the four types of loft conversion? Rooflight, dormer, hip-to-gable and mansard are the traditional four. Most 2026 guides now add a fifth, the L-shaped dormer, because it suits Victorian terraces with a rear back addition and produces a bedroom plus an en-suite rather than a single room.

What is the cheapest type of loft conversion? A Velux or rooflight conversion, from £20,000. It is cheapest because the roof shape is left alone, so there is no structural rebuild. It only works if your loft already has enough head height. If it does not, the cheapest real option is a dormer at £30,000.

Which type of loft conversion adds the most space? A mansard, because it rebuilds the roof to near-vertical and creates a full storey rather than a room in the roof. It runs £45,000 to £60,000. For most houses a dormer gives the best space for the money at £30,000, since every metre built out is full-height floor.

What type of loft cannot be converted? Lofts without enough height in the right places, roofs built with W-shaped trussed rafters, houses with nowhere to fit compliant stairs, very shallow roof pitches, and leasehold flats where the roof space belongs to the freeholder. A survey settles it quickly.

Do all types of loft conversion need planning permission? No. Many stay inside permitted development. Rooflight work is the most likely to, because the roof shape does not alter. Mansards are the least likely, since they change the roof profile substantially. Conservation areas remove permitted development for roof extensions, so check your address.

Verdict on Types of Loft Conversion

Start from the roof, not from the picture you liked. The types of loft conversion open to you are decided by what you already have above the ceiling, and every other question follows from that.

If the loft is tall enough, price a rooflight conversion first. It starts at £20,000. If it is not, the workhorse is a dormer, from £30,000.

Semis with a hipped roof want a hip-to-gable at £35,000. Terraces with a back addition want an L-shaped dormer at £45,000. Only reach for a mansard when nothing smaller will do the job.

Book a survey before you set a budget. Ten minutes in the loft is worth more than a week of reading, including this.