Blog>Cost Guides>Loft extension cost calculator to find approximate price
Last updated: 24 January 2025
Loft extension cost calculator to find approximate price
Creating a great deal of space in any home, a loft extension is easier than ever with easing of government restrictions. When you're budgeting for a large project like this, it can often help to use a tool like our loft extension cost calculator.
Using cost calculator for loft extension projects
To get the most out of our free-to-use loft extension cost calculator, you'll need to know a few details:
Type of loft extension (Mansard, Hip to Gable, Dormer)
What services you might need
The approximate area (by floor space)
What type of roofing you require
Why not try it out today? You can get a rough idea to help start planning ahead.
Enter the approximate size (m2):
Add service (choose required)
Item | Avg Unit Cost | Your Cost |
|---|---|---|
£133.00 per m² | ||
£155.00 per m² | ||
£150.00 per m² | ||
£150.00 per m² | ||
£150.00 per m² | ||
£120.00 per m² | ||
£150.00 per m² | ||
£92.00 per m² | ||
£170.00 per m² |
Scaffolding (pick extension type)
Item | Avg Unit Cost | Your Cost |
|---|---|---|
£158.00 per m² | ||
£158.00 per m² | ||
£80.00 per m² |
Structural alterations / steelwork (pick extension type)
Item | Avg Unit Cost | Your Cost |
|---|---|---|
£200.00 per m² | ||
£150.00 per m² | ||
£100.00 per m² |
Roofing (pick extension type)
Item | Avg Unit Cost | Your Cost |
|---|---|---|
£275.00 per m² | ||
£200.00 per m² | ||
£100.00 per m² |
Roofing alterations (pick alteration type)
Item | Avg Unit Cost | Your Cost |
|---|---|---|
£167.00 per m² | ||
£122.00 per m² | ||
£100.00 per m² |
Doors and Windows (pick extension type)
Item | Avg Unit Cost | Your Cost |
|---|---|---|
£180.00 per m² | ||
£100.00 per m² | ||
£100.00 per m² |
A new loft extension could cost approximately:
£0.00
Working with professional estimators, we collate cost estimates for the common home improvement and repair jobs in the UK. All the costs are estimates only and for accurate costs for your particular requirements, you are encouraged to reach out to professional tradespeople to receive a quote for your job. Read our disclaimer for more information.
With a few clicks, you'll have a rough idea of overall cost. However, you need to be aware that this is only an estimated cost. It is for reference and only to be used as a rough guide.
When you want to get an accurate quote for your loft extension, then speaking directly to local, quality tradespeople is usually the best way forward.
Search for checked tradespeople working in your area
Factors to consider with loft extension costs
With larger projects around the home, there is often a lot of planning involved. It is why most people will opt for project management, which can cost around £4,000. That is based on an average style extension of conversion (around 30m² in size).
Having someone to plan all of the different aspects of the loft extension (or conversion) will make the project go smoothly.
It is also a good idea to understand all of the different aspects of the project yourself, in order to avoid surprises when it comes to the work being carried out.
Type of extension
Different type will affect the overall price, so this needs to be reflected with choices in the cost calculator.
You'll need to consider the main three types:
Mansard - these will often involve roof alterations and may be at the rear of a home
Hip to Gable - these are popular for semi-detached properties, and extend a sloped hip roof to create a gable (vertical wall with flatter roof)
Dormer - these are the most popular, and add a 'box' structure for added space
If you are considering a loft extension, but aren't sure where to start, then speaking to a loft extension specialist would be an obvious place to begin.
Roofing costs
If you are extending, rather than simply converting, your loft, you might need extra work to be done. There will be different pricing according to the type of roofing work you require as part of the overall extension.
Relevant services
Having someone to manage the extension work is often required, as they can liaise with relevant tradespeople for different parts of the work.
For example:
Joinery
Structural changes - i.e. brickwork or steelwork
Plastering
Painting / Decorating
Electrics / lighting
Plumbing
Heating
Flooring / carpets
Doors / windows
Staircase (or loft ladder) - with the extra space, you will need better access
On top of that, for most loft-based jobs, especially extensions, you will also need to factor in the cost of scaffolding. This will depend on the type of work you are having done.
Installation
With much larger projects such as loft conversion, the cost of installation will usually be included in the overall price.
If you've established that your house is suitable for loft extension or conversion, then you'll probably want to speak to a specialist about what happens next.
Using our cost calculator will be able to give a rough idea of price, whereas a loft specialist will be able to give you a detailed quote.
Make sure to check all prices are included in the quote, for example, the cost of installation.
Understanding the pricing calculator
When you're looking to set aside money for a loft extension, it is helpful to have a rough overall cost in mind.
Costs used in the calculator come from our professional estimators, who are Chartered Members (MRICS) of the Royal Institution of Chartered Surveyors and Members of the Chartered Institute of Building (MCIOB).
You will need to think about:
The legalities of the work (permission or permits)
The type of extension
Any relevant services
However, the loft extension cost calculator isn't comprehensive. The following aren't included in the calculator, and could be factors in the final price:
VAT
Skip hire
Planning permission (if required)
Insulation work (if not included)
Building regulations approval (if not included)
Ideally, for a more accurate cost, you would still speak to a loft conversion (or extension) specialist in your local area.
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