The average cost of a dormer loft
conversion is around £45,000
Pricing guides

How much does a dormer loft conversion cost?

The dormer loft conversion costs in this article are correct as of 2022

Dormer loft conversions are one of the most common forms of loft conversion, leading to a common question: "How much does a dormer cost?"

There are three main elements that will affect the price of a dormer loft conversion:

  • The size of the property and overall conversion
  • The number of dormers being added
  • The finish of the conversion; for example, are you installing a bathroom?

Dormer loft conversion cost calculator

Taking as a basis three typical properties with an appropriate number of dormers, with a price for a basic conversion as well as incluidng a bathroom, we can break down the costs like this:

  Two-bed terrace Three-bed semi Four-bed detached
Number of dormers Two Two Four
Basic £30,000 £45,000 £60,000
Bathroom £2,000 £4,000 £6,000
Total £32,000 £49,000 £66,000


As an addition to this, are all the other costs involved in the loft conversion - adding a staircase, insulating the space, strengthening the floors, fixtures and fittings and so on.

We have found that the standard cost of a dormer loft conversion ranges from around £30,000 to nearly £66,000 depending on the size and scope, with a typical price coming in around £45,000.

Though they are cheaper than some other forms of loft conversion, you will still need to set aside a good budget to get the work done. We’ve spoken to some of the experienced loft conversion specialists at MyBuilder to break down the process.


Stages of a dormer loft conversion

When carrying out a dormer loft conversion, there are a number of stages, from planning, to fitting and finishing. Here is what you can expect.


Dormer loft conversion plans cost

You will need to have plans for your dormer loft conversion drawn up either by an architect, or by an architectural technician, or surveyor, laying out the design for the project.

Your plans should take all of the structural alterations needed into account, and will cost in the region of £1,000 plus VAT.


Planning permission costs 

Most dormer loft conversions will not require planning permission as they are considered permitted developments.

However, depending on the scale of the work, and other factors such as its impact on the street scene, planning permission may be required.

Applying for planning permission currently costs around £200 in England. 


Building regulation costs 

Regardless of your planning status, your dormer loft conversion will have to be inspected by the building regulations department of your local authority to ensure it is being constructed in accordance with the rules, making sure it complies with things like fire safety, access, floor strength and so on.

Submitting the plans for inspection and having on-site inspections can cost between around £400 and £800.

You may also need a Party Wall Agreement if your work will impact any adjoining properties, for example if you live in a terraced house or a semi-detached home. This requires your neighbours to agree to the work taking place.

You are liable for costs such as their surveyor and any damage to their home which may occur as part of the works - it can cost several thousand pounds depending on how complex the agreement is.

Another potential cost, though not always needed, is a bat survey if you believe your loft may have bats - this can cost up to £400.


Dormer loft conversion building costs

When work begins, the initial construction will be carried out externally, with the use of scaffolding and in some cases a roof cover to allow work to continue effectively even with bad weather.

At some point, access will be created into the loft from the interior and the floor will be strengthened. The dormers will be constructed and the roof altered.

Interior walls will be then be fitted along with insulation, and features such as the staircase will be installed, followed by windows.

Electrics and plumbing will go in, before it is plastered and carpentry such as skirting boards are fitted.

Electrical sockets and elements like the WC and sink, if needed, are then added, before the final conversion is ready for final inspection, and decoration can then take place.

This is where the bulk of the costs are spent.


Other dormer loft conversion costs

The standard of fixtures and fittings in the loft will have a large impact on the cost of the project .

For example, if you are simply planning to use the space as a large bedroom, it will be cheaper than if you are putting a bathroom in the space, where you will need to purchase the suite, which can cost several thousand pounds.

Moving the property’s water tanks if needed, and altering the rest of the home’s plumbing system, will also add to the overall price.

A slate roof will usually cost more to alter than one with concrete roof tiles.

Another factor is whether the roof was built with a frame - often found in pre-1960s homes - or with wooden trusses, which are easier to construct but can take less weight.

Replacing or reinforcing the trusses can take more work and thus increase the costs.

MyBuilder Top Tip

Before you begin planning your dormer loft conversion, think about what you want to use the space before.

Your budget may restrict the number and size of the dormers you wish to install, but if you don’t add enough to make the room feel truly useful, it will only be money wasted in the long run. 

How long does a dormer loft conversion take?

The actual building portion of a loft conversion will usually take between six to eight weeks.

However, the planning stage can also take a considerable amount of time, especially if planning permission is required and a Party Wall Agreement needs to be negotiated.

You will typically be able to stay in your home throughout the duration of the work though, without too much disruption.

Get a loft conversion quote

We can help you meet professional loft conversion builders near you to get real quotes today.

How to keep your dormer loft conversion costs down

Hiring trustworthy tradespeople is the best way to ensure your job comes it at a fair price with no unnecessary additions.

At MyBuilder, we typically advocate hiring particular specialists for each role, however, with dormer loft conversions, there are a number of ways of hiring the necessary tradespeople.

You could hire an architect to plan and let them oversee the entire project, hiring a team of builders and other necessary trades, or hire a specialist loft conversion firm who will have a team with all the needed skills.

You can also project manage the work yourself, hiring different tradespeople for different elements of the build, but it will require a lot of attention to ensure each stage runs to schedule and does not cause delays.

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