Loft Conversion Cost & Prices 2021

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

Firstly, roof conversions are often covered by Permitted Development Rights (PDRs) which have become increasingly relaxed in the UK – that means there’s often no need for obtaining planning permission (more on this in a moment). 

Loft conversions can increase the value of a home by some 20%, which essentially works out as a win-win in many situations depending on the existing value of your home and the cost of the conversion.

Of course, you also have to factor in the use you get out of the conversion and how this enables you to add space to your home without moving. 

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 Loft Conversion 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)

£55,000+

(two or more dormers, L-shaped dormers)

£60,000+

(two or more windows)

£60,000+

(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 

Planning Permission For Loft Conversions 

In the UK, Permitted Development Rights (PDRs) enables residential property owners to make certain modifications to their home without planning permission. 

Loft conversions are one such modification permitted under PDRs, granted certain conditions are met. 

You will not need to seek planning permission for loft conversions that:

  • Do not exceed the original height of the roof.
  • Do not amount to an extra volume of 40 cubic metres or more for terraced houses; or
  • 50 cubic metres otherwise. 
  • Cannot include verandas or balconies without planning permission.
  • Listed buildings, areas under Part 4 planning directions or various conservation areas and designated areas not covered by PDRs. (Planning Portal, 2021)

There are other laws and regulations to bear in mind such as the Party Wall Act, for work that involves work to shared walls. The extended roof must also pose no obstruction to neighbours. 

In these situations, PDRs can still apply, but you must instead seek Prior Approval which involves consultation with neighbours. 

Before you start work, it’s recommended you obtain a Lawful Development Certificate to avoid any legal issues. 

Loft conversions are also subject to Building Regulations. You can discuss this with your surveyor or architect who will be your main touch-point when it comes to adhering with laws and regulations. 

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)

Project Timeline 

Loft conversions are generally much speedier than typical extensions because they only involve minor modification to external walls (depending on the conversion type and size). 

With everything taken into account, the average duration of loft conversions is 4 to 8 weeks. If you need to obtain planning permission then this can take another 4 – 8 weeks. 

Prior Preparation 

In terms of upfront payments for the loft conversion, you will have to pay for the architect and surveyor fees including any technical drawings you need for planning permission/approval.

It’s common to pay a deposit for the building work (usually 20%). Other payments will be made according to a payment schedule.

Prior to undertaking any work whatsoever, you should consider hiring a Chartered Surveyor to inspect your loft, advise on planning permission and suggest what is and isn’t possible. 

Your chosen architect may work with a surveyor. They’ll hold a consultation which will include a structural inspection and draft planning. 

Many loft conversion firms manage the entire project, including assistance with a planning application if required. 

  • Your architect and surveyor will advise you if you require planning permission or Prior Approval, and should be able to provide architectural drawings that greatly enhance your chance of receiving immediate permission.
  • Your specifications will also have to align with Building Regulations. Your architect and surveyor will need to clear the project with Building Control.
  • Where planning permission is not required, most loft conversion specialists recommend or require you to obtain a Lawful Development Certificate.
  • Planning permission takes around 8 weeks on average. Prior Approval can be sorted in a matter of days providing there are no objections.

Scaffolding 

Week 1 will involve scaffolding and securing the workplace. Your architect or project manager will assemble contractors and the roof will be opened up. 

Securing the Floor/Foundations

The next step is securing and reinforcing the floor. Timber or steel reinforcements will be put in place to secure the walls, joists and flooring. 

Installing the Dormer/Window/Mansard

The next step is the installation of the chosen loft conversion. Dormers and mansards can usually be installed within a few days to a week. Velux windows are much quicker to install. 

Insulation 

Insulation is imperative for building regulations and will be installed as the external walls are reassembled with the conversion. Ventilation may also be built into the floorboards to prevent overheating. 

Staircase 

The new staircase will be installed midway or towards the end of the project. 

Electrical/Plumbing/Plastering

Once major structural works are complete, electrical, plumbing and plastering work will be carried out. 

Once complete, a complete evaluation of the project will be made and summaries drafted for checking with the council’s building control. 

Get Prices on Loft Conversions Heating 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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