Types of loft conversion: the four main types, compared

There are four main types of loft conversion: a rooflight (velux) conversion, a dormer, a hip to gable and a mansard. In 2026 they cost £30,000 to £96,000 or more including VAT, and your roof decides which of them are open to you before your budget does. We compare what each one changes, its price, build time and planning route, the houses each suits, and the three variants.

The four types of loft conversion at a glance

The types differ in how much of the roof they rebuild. The more of it that changes, the more room you gain, and the more the work costs and the longer it takes.

Prices include VAT at 20% and cover the conversion itself. The time on site comes after 2 to 3 months of drawings, structural calculations and approvals. If the loft is part of renovating a house, book it near the start, because structural work and roofing come before the services, insulation and finishes.

Rooflight (velux) loft conversion

A rooflight conversion keeps the roof exactly as it is. Windows go into the existing slope, flush with the tiles, and the rest of the work happens inside: a new floor, insulation, a staircase and the fit-out. Most people call it a velux loft conversion, after the roof window brand.

It is the cheapest and quickest type, at £30,000 to £48,000 including VAT and 4 to 6 weeks on site. Because it adds no volume, it only works where the loft already has the height, on a steep roof, ideally pitched at 40 degrees or more. That makes it the usual choice for bungalows and houses with tall roofs.

In England, rooflights are permitted development if they project no more than 0.15 metres from the slope and sit no higher than the highest part of the original roof, so they can go on a front slope where a dormer facing the road cannot. Rooflights in a side slope have to be obscure-glazed.

Dormer loft conversion

A dormer loft conversion builds a box out from the roof slope, with two side walls called cheeks, a front wall that carries the window and, usually, a flat roof. The vertical walls turn the low edges of the loft into full-height floor, and a dormer across the rear slope typically gives 15 to 20 square metres.

A dormer costs £42,000 to £72,000 including VAT and takes 6 to 10 weeks on site. It suits terraced and semi-detached houses. In England a rear dormer is usually permitted development, within 40 cubic metres of added space on a terrace or 50 on other houses, while a dormer on a front slope facing a road needs an application.

A dormer need not be a flat-roofed box. A pitched dormer carries its own small sloping roof and gives less room, and several small pitched dormers suit a conservation area, where any dormer needs planning permission.

L-shaped dormer

An L-shaped dormer joins two dormers, one over the main roof and one over the rear outrigger of a Victorian or Edwardian terrace. It gives 25 to 35 square metres, against 15 to 20 from the rear slope alone, which is room for two bedrooms and a bathroom.

It costs £60,000 to £90,000 including VAT and takes 8 to 10 weeks on site. The valley where its two roofs meet is the most common leak point on a badly built L-shape. The steels usually span from the party wall to a new post over the outrigger, and on a terrace the neighbours on both sides get a party wall notice.

Hip to gable loft conversion

A hip to gable conversion takes the sloping end of a hipped roof and rebuilds it as a vertical gable wall. The loft no longer narrows to a point at that end, which adds a large amount of headroom and floor area.

It suits detached, semi-detached and end-of-terrace houses with a hipped roof, and it is not possible on a mid-terrace, which has no hipped end. The typical candidate is a 1930s semi, and most of those pair the hip to gable with a rear dormer to use the full width of the back slope.

A hip to gable costs £54,000 to £78,000 including VAT and takes 10 to 14 weeks on site. In England it is usually permitted development. The 20 centimetre set-back from the eaves does not apply to it, but on a semi the new gable and any rear dormer share one 50 cubic metre allowance.

Mansard loft conversion

A mansard conversion rebuilds the rear slope as an almost vertical wall, at 72 degrees or steeper, under a flat roof. It gives the most room of the four main types.

It is also the dearest of the four: £66,000 to £96,000 or more including VAT, and 10 to 12 weeks on site. Because it changes the shape of the roof, it normally needs planning permission in England, and on a terrace a party wall agreement with the neighbours on both sides comes as standard.

Mansards are common on London terraces. With a piggyback, a mansard is one of the two routes left when the loft is too low for a dormer.

Piggyback and modular loft conversions

A piggyback conversion lifts the whole roof to create head height the loft does not have. At £72,000 to £108,000 including VAT and 10 to 12 weeks on site, it is the dearest route. Nothing built under permitted development may rise above the existing roof, so a piggyback always needs a planning application, and a party wall award where walls are shared.

A modular conversion is built in a factory and installed complete. It costs £54,000 to £84,000 including VAT, and the factory build cuts the time the house is open to the weather to a day or two, with 3 to 5 weeks on site. Its planning route follows the shape of what is installed.

Which type of loft conversion suits your house

The house and the shape of its roof narrow the choice before the budget does. A hipped roof slopes down on all four sides, so one end has to be rebuilt before a dormer can run the full width. A gable roof already has vertical ends.

• Mid-terrace: a rear dormer, or an L-shaped dormer where there is an outrigger, and a mansard where the loft is low. A hip to gable is not possible.
• Semi-detached with a hipped roof: a hip to gable with a rear dormer, sharing one 50 cubic metre allowance in England.
• End of terrace: a hip to gable where the end of the roof is hipped, otherwise a rear dormer.
• Detached: the widest choice, with a 50 cubic metre allowance in England and no shared wall to build off.
• Bungalow: a large footprint, and a rooflight conversion where the roof is tall and steep. Bungalows built from the 1960s on tend to have shallow trussed roofs with little height.

No type works under a flat roof, because there is no loft to convert. A flat or maisonette has no permitted development rights for a roof, so any loft conversion there needs a planning application.

Which lofts cannot be converted

Three facts about the roof decide which types are possible: the height under the ridge, the pitch and how the roof was built.

Measure from the top of a ceiling joist to the underside of the ridge. The new floor, insulation and plasterboard take 250 to 400 millimetres of that before there is a finished ceiling.

Houses built before about 1965 usually have a cut roof, assembled on site from rafters, purlins and struts, which converts with steel beams and modest carpentry. Almost every house from the mid-1970s on has trussed rafters, thin factory-made frames with W-shaped webs. Converting those means taking the trusses out, new steel at wall plate level and a new floor hung from it, which adds £5,000 to £15,000.

Attic trusses, used on some newer estates, are the exception. They are built with a clear space in the middle.

What each type of loft conversion costs

The price of each type follows how much roof it rebuilds. Including VAT, loft conversion prices run from £30,000 for a rooflight conversion to £96,000 or more for a mansard, and London sits about 17% above the UK figures.

No official body publishes loft conversion prices, so these are market rates for the conversion itself. The staircase, the steel for the new floor, the fees and any en suite usually sit outside them, whichever type you choose.

Planning permission for each type

In England, a rooflight conversion, a rear dormer and a hip to gable usually count as permitted development and need no planning application. The limits for a loft are:

• No more than 40 cubic metres added on a terraced house, or 50 on other houses, counting earlier roof enlargements.
• Nothing higher than the existing roof, and nothing beyond the front slope where it faces a highway.
• A set-back of at least 20 centimetres from the original eaves where practicable, except on a hip to gable.
• Materials similar in appearance to the house, and no verandas, balconies or raised platforms.
• Side windows obscure-glazed, with any opening part at least 1.7 metres above the floor.
• Not a flat, and not on designated land such as a conservation area or National Park.

A mansard, a piggyback and a front dormer facing a road break those limits, and so does an L-shaped dormer that adds more than 40 cubic metres to a terrace. A listed house needs planning permission and listed building consent for any type.

Where you need planning permission for a loft conversion, the householder fee in England is £548 and a decision is due about 8 weeks from validation. Where the design fits the limits, a £274 lawful development certificate confirms it in writing before work starts.

Building regulations for every type

Every type needs building regulations approval from the council or a registered building control approver, including a rooflight conversion under permitted development. The checks cover the structure, fire safety, the stair and insulation.

A loft room adds a storey, and that changes how people get out in a fire. On a typical two-storey house, the fire safety guidance for loft conversions calls for fire-resisting doors, and sometimes partitions, to protect the stairway, because escaping through a window above first floor level is too dangerous. Mains-powered, interlinked smoke alarms go in the stairway at each level.

Every type also needs a proper stair, since a retractable ladder is not normally acceptable. The stair rules ask for 2 metres of headroom, relaxed for a loft to 1.9 metres at the centre and 1.8 metres at the side, and that often decides where the stair can land.

Every conversion also needs a structural engineer's calculations. When the finished work complies, the council issues a completion certificate, usually within 8 weeks, and a buyer's solicitor will ask for it.

Which type adds the most value

Value follows the rooms rather than the type. Nationwide's house price research puts an extra double bedroom on a two-bedroom house at around 13% of its price, and a bedroom plus a bathroom at up to 24%. A room whose stair falls short of the headroom rules is valued as a loft room, not a bedroom, and the uplift stops at the ceiling price for your street.

Loft conversion types in Wales, Scotland and Northern Ireland

Everything above is England's. Wales, Scotland and Northern Ireland write their own roof rules and have their own building standards, and the Party Wall etc. Act 1996 covers England and Wales only. In all four nations, raising the roof and building a roof extension in a conservation area fall outside permitted development, so a piggyback always needs an application.

The Welsh loft rules keep England's volume limits and rule out uPVC on a dormer other than, possibly, for the windows. Side windows within 10.5 metres of a boundary have to be obscure-glazed or non-opening.

Scotland controls a dormer by where it sits rather than by its volume. Under the Scottish householder circular of 2024, rooflights may project up to 1 metre, but not in a conservation area.