How much does a loft conversion cost in 2025?

A loft conversion can be a great way to add value and living space to your home, but it doesn't come cheap.

To find out how much a loft conversion costs in 2025, the Building Cost Information Service (BCIS) provided us with typical costs for different sizes of rooflight and dormer conversions.

We also share expert tips on how to save money on your loft conversion.

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Loft conversion costs 

The cost of a loft conversion can vary dramatically based on size and quality.

Our prices for rooflight and dormer conversions include include labour and materials. 

They cover clearing of materials from the loft space, relocating an existing water tank, insulation of walls and ceiling, softwood framing (where wood is placed to make new structures), plasterboard on walls and ceiling, a new straight flight of stairs, new electrics and heating.

The costs don't cover internal partition walls and painting and final decoration.

Rooflight loft conversion costs

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Dormer loft conversion costs

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Loft conversion cost breakdown

There are a number of factors which will impact the amount you have to spend on each element of your loft conversion - for example, if you need to use an architect.

However, your total bill will likely be made up of a combination of the following:

• Labour costs: 35% - 40%
• Materials: 25% - 30%
• Fixtures and fittings: 10% - 15%
• Planning and permissions: up to 5%
• Contingency budget: up to 10%

We recommend you always include a contingency budget of 10% of your total budget (or more), to cover for any issues that might arise during the project. 

How the costs are calculated 

The Building Cost Information Service (BCIS) database analyses price data from a variety of sources. 

Materials costs are based on the best trade prices from a range of suppliers across the UK, which are then benchmarked to reveal the best national average.  

Labour rates are based on the current Building and Allied Trades Joint Industrial Council wage agreement. 

All of this data is put into a standardised model of an average loft conversion. The prices include everything to carry out a loft extension job, including labour, materials, any preliminary work, contractor overheads and profit and VAT.

Prices are correct as of November 2024. 

Wondering where to start with your loft conversion? Read our guide on how to plan a loft conversion

What other factors affect loft conversion costs?

The cost of a loft extension can vary significantly. Some common factors that will influence the cost include:

• The type of conversion
• The type of roof 
• House location 
• Whether you need planning permission
• Whether you need a party wall surveyor

Type of conversion 

Conversions that require structural work (such as dormer or mansard) will cost more than a rooflight conversion. 

The type of room you convert your loft into can also drive up prices. 

If you're having a bathroom fitted, for example, it will require more pipework and take more time, resulting in a higher overall cost. You should also consider what the water pressure will be like and whether you need to reinforce the floor to support your sanitaryware.

That said, larger-scale conversions tend to have a greater return on investment when it comes to selling your house. 

Type of roof

The type of roof on your house can make a big difference to the amount of structural work that needs to be carried out.

Houses built before 1970 tend to have old-style rafters; these are open and self-supporting, making them easier to convert.

Houses built after about 1970 often have roof trusses – a framework that spans the cross-section of the roof. These are trickier to convert, as more work is needed to make sure they remain structurally sound, and it can double the cost.

If you can see beams cutting across the centre of your loft space, your house has roof trusses. If the timber is restricted to the edges of the roof, you have rafters.

House location 

The area you live in is likely to have an impact on the cost of your conversion, which there isn't much you can do about.

Typically, if you live in Northern Ireland you will pay less, while if you're in southeast England you'll pay more.

If you live in London, the higher cost of labour and materials mean you're likely to face higher costs than anywhere else in the UK. However, you should also see a greater return on your investment, as space is at a premium in the capital. 

Whether or not you need a party wall surveyor

If any of the work you do affects the adjoining wall between your house and your neighbour's, you'll need to serve your neighbour with a Party Wall Notice. This outlines the work you're proposing and should include detailed plans.

These can be straightforward, but if your neighbour is concerned, they are within their rights to appoint a surveyor to come and look at the plans. If this is the case, it's up to you to cover the costs.

Improve your chances of keeping costs fair by including some suggested surveyors with your Party Wall Notice. Ask your builder or architect to recommend reputable companies.

Read Will I need a party wall agreement for a loft conversion? to find out more

Whether or not you need planning permission

Most loft conversions can be carried out without planning permission but, if you do need it, you'll have to pay for the application, which can cost up to £1,000.

Find out whether you will need planning permission early on, so you can consider it within your overall budget – it may be that you'll need to spend less elsewhere to compensate.

Read our guide to loft conversion building regulations and planning permission for further information

Does a loft conversion add value to your property?

A well-designed loft conversion can add up to 20% to the value of your home.

However, this varies significantly depending on the type of conversion and where you are based.  

Adding another bedroom with an en-suite – creating a new primary bedroom – will yield the greatest returns. 

Loft conversions will add more value to your home in London and the South East, where space is at a premium, than in the North and South West. 

Is it possible to DIY a loft conversion?

It is not possible for most homeowners to DIY a loft conversion - especially if you plan to use the space as a living area (ie, rather than for storage only).

Not only will you need extensive knowledge of structural works (including load bearing requirements), but if you do not perform the DIY correctly, this can cause catastrophic failure. 

You can save costs on labour by decorating the loft yourself, but it is best to leave the rest to a professional. 

How to save money on a loft conversion

These tips should help you shave money off the cost of your loft conversion: 

• Get more than one quote: We recommend you get at least three quotes for any building work to ensure you pay a fair price
• Ask for a fixed-price contract: The price of a fixed contract cannot go up or down except in the case of certain predefined circumstances, so you won't have any nasty surprises later on
• Add a contingency budget: Add 20% to your total budget to cover unexpected additional costs 
• Find your own fixtures and fittings: There are plenty of deals to be had by looking online; second-hand and auction sites such as eBay can be a cost-effective option.