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Loft Conversion Cost & Prices 2023

Loft conversions are one of the most popular forms of extensions in the UK. They yield several important advantages over typical house extensions. 

This article will cover what you can expect to pay for a loft conversion, factors that can affect the cost and other common questions around loft conversions.

Average Cost

The following cost guide includes project planning and architect fees, surveying costs, building costs and materials, staircase fitting, plastering, flooring and basic interior design, plumbing and electricity (but not boiler relocation). 

These costs are compiled from 15 architecture agencies and loft conversion specialists across the UK. 

  Velux Dormer  Mansard  Hip-to-Gable
5 x 4 m2 (20m2)

1 room 

£12,000 to £20,000 (one window) £28,000 – £35,000

(one dormer)

£30,000 – £45,000

(one window)

£30,000 – £45,000

(one window)

5 x 6 m2 (30m2)

1 room

£15,000 – £20,000 (one window) £30,000 – £38,000

(one dormer)

£35,000 – £48,000

(one window)

£35,000 – £48,000

(one window)

6 x 8 m2 (48m2)

1 to 2 rooms

£20,000 – £24,000 (two windows) £40,000 – £50,000

(two dormers)

£45,000 – £50,000

(two windows)

£40,000 – £48,000

(two windows)

8 x 8 m2 (64m2)

2 rooms

£25,000 – £30,000 (2+ windows) £45,000 – £55,000 

(two dormers)

£50,000 – £60,000

(two windows)

£50,000 – £60,000

(two windows)

8 x 12 m2 (96m2)

2 rooms +

£30,000 +

(only applicable to exceptionally large lofts)


(two or more dormers, L-shaped dormers)


(two or more windows)


(two or more windows)

Loft conversions range from some £12,000 for the simplest projects to far in excess of £60,000 for large multi-room projects. 

Beyond the top bracket, the sky’s the limit (granted planning permission!).

Very large loft conversions that build over existing extensions can create 3 or even 4 more rooms, and for that, you could be looking at costs exceeding £75,000. 

Such loft conversions are only an option for large detached houses with plenty of existing space and ample structural support. 

Factors That Affect the Cost of Loft Conversions

The cost of loft conversions vary depending on the following factors:

  • Your desired loft conversion type and size 
  • Your location within the UK
  • Your property and its age
  • Relocation of the boiler (can cost upwards of £2000 if it has to be relocated entirely) 
  • Fitting of toilets or bathrooms (can cost upwards of £3000)
  • The type of insulation you choose (there is a minimum requirement to meet building regulations) 
  • Any interior design and optional extras 

Main Types of Loft Conversion 

There are 4 main types of loft conversion. Each differs in design, construction and cost. 

For some properties, your options may be limited due to the design of the roof. Shallower roofs are more confined and may not provide sufficient headroom without modification to the external walls. 

Velux Loft Conversion 

The simplest, cheapest type of loft conversion. Velux loft conversions install windows into the roof and fit it out for occupation. That includes access via a staircase, insulation, plumbing, electricity and windows. 

Velux loft conversions are straightforward for houses with large loft spaces and deep roofs. 

There may not be enough space for a Velux conversion in homes with shallow roofs. 

  • Cheapest option
  • Almost never involve planning permission (but building regulations still apply)
  • Great for homes with larger lofts, or when just one small room is needed

Dormer Loft Conversion 

The most popular variety of loft conversion. The dormer loft conversions add a protruding window to increase interior space whilst offering a natural, vertical window (in oppose to a Velux window). 

Dormers can be created singly or in pairs. Full-length or L-shaped dormers are also possible for extending the loft conversion over already-extended buildings (planning permission will be required).

  • Suitable for most homes
  • Rarely involve planning permission 
  • Variety of shapes and formats

Mansard Loft Conversion

Mansard loft conversions are similar to dormer loft conversions but the new exterior wall gently slants backwards (typically at a 72-degree angle) to smooth out the exterior appearance of the conversion. 

They add more space to the new window-side of the conversion compared to dormers. 

Mansard loft conversions are more expensive than dormer conversions and more frequently involve planning permission. 

  • More space than dormers
  • Generally more aesthetically pleasing and less protrusive (could be necessary for planning permission)
  • Can be big or small 

Hip-to-Gable Conversion

Hip-to-gable conversions involve the inwardly slanted end or side roof. 

Instead of creating a new roof extending from the back or front of your house (e.g. the same direction as most existing bedroom windows), hip-to-gable conversions extend to the left or right-hand side of the roof. 

This often avoids interfering with shared party walls.  Hip-to-gable conversions can be combined with dormers to add 2 or even 3 extra rooms (will require planning permission). 

  • Suitable when dormers or mansard conversions aren’t possible
  • Make use of the sides of the roof 
  • Common in end-of-terrace houses (as no party wall modifications are required)

Get Pricing on Loft Conversions Near You

We’ve done our best to give you a good idea of what you can expect to pay for a loft conversion.

However, our guides are not a substitute for a fixed quote specifically for you.

We work with all the best loft conversion specialists ready to price your job. Get free, no-obligation quotes in your local area and compare prices using the form below.

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About the Author

Alex Johnson is a qualified quantity surveyor and writer with a passion for conducting original research and uncovering the true cost of jobs. His cost data has been referenced by EDF Energy and the Scottish Government.