Loft conversion cost calculator – How much will your loft conversion really cost in 2026?
Loft conversions are one of the most effective ways to add extra valuable space to your home – whether that’s through adding a bedroom, a playroom, home office or an extra bathroom.
Rather than extending outward, a loft conversion makes use of the area you already have and creates usable space by transforming an underused roof void into a high-quality living accommodation.
But how much does a loft conversion cost in 2026? And what exactly should you factor in when it comes to budget for a loft conversion project?
This loft conversion cost calculator guide breaks down everything you need to know – from typical construction costs in London and across the UK, to professional fees, VAT and the hidden expenses that are often overlooked.
While every project is different, understanding the key cost drivers will allow you to estimate your likely investment with far greater accuracy.
Many properties in the UK are suitable for a loft conversion and a large number fall under ‘permitted development’ meaning that planning permission is not required. This makes a loft conversion one of the most cost effective ways to expand space in your home .
However, costs can vary significantly, depending on the type of loft conversion, the size and shape of your roof, the level of specification and the complexity of the design.
In this guide, we aim to:
Before we dive in if you’d like to discuss your project with us. You can get in touch here.
If you’d like to learn more about loft conversions, you can read our loft conversion planning guide here.
So you’ve decided that you want to start exploring a loft conversion project but you’re likely weighing up two key questions: What are the average loft conversion costs involved and is the project complexity actually worth it for your home?
From a purely financial perspective, moving home in London is expensive.
In 2026, the cost of moving can reach approximately £50,000 or more once stamp duty, legal fees, estate agent fees, removals and associated costs are considered. This is assuming you are purchasing a property with a value of around £1million. If the property is more expensive, then these costs can increase drastically.
And that figure doesn’t account for the time, disruption and stress involved in the process.
By contrast, a loft conversion allows you to gain additional space without leaving a home and neighbourhood you already enjoy.
For many home owners, this therefore makes it a far more strategic long-term decision.
A well-designed loft conversion can increase a property’s value by 20%, depending on location and specification.
In London in particular, where square meterage is at a premium, adding another bedroom and bathroom can signficantly enhance resale value and buyer appeal.
It has been said that adding an en-suite bathroom typically increases the cost of a loft conversion by £5,000 to £12,000.
While no investment is guaranteed, loft conversions consistently rank among highest-return home improvement projects.
As you can see, the cost of construction in London can be higher than the rest of the UK. This is especially true when work is being carried out on an existing building, where structural alterations, access constraints and higher labour costs can all influence pricing.
That said, loft conversions can still offer efficiencies in both time and cost – particularly when compared to other types of extensions that may require full planning permission and extensive structural alterations.
It’s important to remember that these are ballpark figures.
The final cost will depend on several factors, including the existing roof structure, the size of the loft, the type of loft conversion and the level of specification.
In some cases, you may not benefit from permitted development rights, meaning a planning application could be required. We’ll explore this later on in the article.
The below section will cover the overall cost for different types of loft conversions and price per square metre.
Generally speaking, more basic conversions such a velux conversion start at around £27,000 while more complex loft conversions often exceed £65,000
The cost of a loft conversion can vary on a whole host of factors which we will dive into in the next section.
The different types of loft conversions include:
A Velux loft conversion is a pretty basic loft conversion and a great option if you’re looking to carry out an attic conversion but keeping the costs and work required to a minimum.
A Velux loft conversion involves installing roof lights or velux windows to let in natural light to the usable space without altering the existing roof structure.
This means they are most suitable for properties that already have a large existing loft space.
As the works are quite minimal, there is the least disruption out of the listed loft conversion options but provide the least amount of extra space.
In general, Velux loft conversion average at around £27,000 in the UK, £920 per m²
A dormer conversion uses your existing roof space and extends out to create additional headroom and space.
It is a good all-rounder option meaning that it is suitable for most types of properties including detached property, semi-detached house and terraced houses and good to maximise space, transforming a cramped attic space into a full-height, airy and bright room.
The process involves adding a box-like structure with vertical walls that attach to the existing roof slope.
The average cost of a dormer loft conversion is around £50,000 in the UK, £1,670 per m²
A hip to gable loft conversion is most common on a semi detached house or end-of terraced home.
The hip to gable loft conversion involves transforming the existing sloping roof into a vertical gable wall. This then significantly increases the internal head height and floor space which is why it is ideal for the above mentioned types of properties.
The gable loft conversion cost comes in on average at roughly £60,000, £2,000 per m²
A modular loft conversion is a type of prefabricated loft conversion that is built off site.
The work for the loft structure takes place in a factory and is created in different sections known as ‘modules.’ These are then delivered to the property by lorry and then installed.
Modular loft conversions are quite complex as they require the entire roof of the existing property to be removed so the pre-fabricated structure can be lifted in place.
The average cost of a modular loft conversion is roughly £45,000, £1,500 per m²
The above price will depend on the project complexity, size and specification (and this can apply to all the mentioned types!)
The mansard loft conversion is one of the most complicated loft conversions and involves altering the structure of the roof to create a flat-roofed box-like extension with sloping walls.
This a premium, high capacity loft conversion altering the existing roof and making a massive increase in usable space.
This conversion is most popular in densely urban areas like London, converting cramped attics into functional space and often being able to accommodate multiple additional rooms.
The mansard loft conversion cost typically come in as the most expensive at around £65,000, £2,170 per m²
A shell loft conversion is a basic loft conversion where loft conversion specialists will come and carry out all structural works of the addition and then leave it to the homeowner or designer as a ‘home improvement project’ to carry out the interiors and finishes.
This loft conversion cost comes in at one of the lowest and is best suited to someone who really enjoys getting involved in construction work – a rewarding challenge!
The average shell loft conversion cost comes in at around £30,000, £1,000 per m²
Every loft conversion is unique, but you can get a good idea of your likely cost by breaking the project down into a few simple steps.
This method works as a ‘loft conversion cost calculator’ – no tools required!
Complexity will impact cost – The type of loft conversion plays a big role. For example, a Velux loft conversion or roof light conversion will be cheaper than let’s say a Mansard loft conversion or Gable loft converison which are both at the top end given the works involved.
Include costs for:
Standard VAT is 20% on most work and its important to note, most headline fees exclude VAT so do remember to factor it in.
Existing structures are highly unpredictable and costs can always vary depending on a whole host of factors including unknown repairs, structural reinforcements needed or specification upgrades.
Contingency ensures you don’t blow your project budget and can account for an unexpected costs or hidden costs.
This could include a bathroom suite, staircase design upgrades, high-spec finishes and material costs that may vary, Velux roof lights or dormer windows.
All of these can impact budget and should be accounted for.
Let’s take a case study of a 20 square metre dormer conversion in London:
Estimated total cost = £71,500
By including the loft conversion type in your calculation and accounting for whether your project is a small loft conversion or full-scale extension, you can make your budget more accurate before approaching loft conversion specialists.
Most loft conversions in the UK will fall under permitted development rights, meaning you often don’t require planning permission.
This makes loft conversions quicker and simpler than other types such as ground or rear extensions.
When you do not require planning permission:
When you may require planning permission:
If planning permission is required, you will need to factor this in both in terms of time and cost to your loft conversion project.
It is a good idea from the outset of your project to consult with the local planning authority to confirm whether planning permission is required for your specific project.
Unlike planning permission, building regulations approval is always required for a loft conversion project. This ensures that your loft conversion complies in terms of its structure, fire safety, proper insulation, safe access, adequate ventilation.
In Scotland, Wales, and Northern Ireland, you usually need a building warrant for a loft conversion to ensure compliance with building regulations.
Key areas that are assessed include structural reinforcements, staircase design and headheight, fire doors and escape routes, thermal insulation and ventilation, soundproofing between floors.
Building control approval is obtained either through your local council or via an approved private inspector and protects both the safety and long-term value of your loft conversion project.
Building regulations typically require a minimum height of around 2.2 meters (7 feet 2 inches) at the highest point for a loft conversion to be considered habitable.
Planning permission fees for a loft conversion can range from £206 to £462, depending on the local authority.
Building regulation fees for a small to medium-sized loft conversion may cost around £300 to £800.
When planning a loft conversion, understanding what each part of the project costs helps you make informed decisions and avoid nasty suprises.
Here is a breakdown of the main conversion cost areas:
Structure and roofing – The structural work is the backbone of any loft conversion and loft conversion cost!
This can include:
Staircase and access – Safe and functional access to your loft conversion is essential.
Loft hatch vs full staircase: The choice can have an impact on usability and budget
Windows and glazing – Natural light transforms the converted space but depending on your glazing choice, the loft conversion cost can be impacted:
Electrical and plumbing – Adding services to your loft space can shift costs significantly.
Plumbing: Installing a new bathroom or en-suite requires drainage and cold water connections
Finishes and decoration – The final touches make your loft space a usable, attractive space:
Professional fees and surveys – Even if your construction costs are controlled, professional input ensures compliance and quality:
Contingency and VAT – As stated above, you need to factor these in from the beginning as both a contingency and VAT will impact your budget.
A well-designed and executed loft extension can add significant value to a property, particularly in areas with high demand for housing like London.
This extension can also be one of the most effective ways to add space and value to your home. Whether you’re opting for a small loft conversion or full-scale transformation, understanding the different loft conversion types is key so you can ascertain the different costs involved and the planning and buillding regulations process required for a successful project.
By breaking down costs into construction, professional fees, finishes and contingency, we can create a realistic budget before consulting loft conversion experts.
Beyond the cost of a loft conversion, the project offers such significant benefits as discussed in the article and can really make your home work better for you and avoid you having to move!
Ultimately, whether your goal is to add a new habitable space, a well-planned loft conversion can provide a practical and beautiful spatial solution.
As with all projects, we recommend getting in touch with a professional to discuss your options. Get in touch today and we’d be more than happy to discuss your loft conversion project!
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