Builders
Carpenters
Electricians
Flooring Specialists
Gardeners
Handymen
Heating Engineers
Painters & Decorators
Plasterers & Renderers
Plumbers
Roofers
Tilers
myMansard Loft Conversion Cost
At a Glance
- The average cost of a mansard loft conversion is around £67,500.
- The job will usually take between 6 - 8 weeks.
- Mansard roof extension prices and factors that impact loft conversion costs.
- How long the job will approximately take and what's involved.
- How to find and hire a loft conversion specialist using MyJobQuote.
Get free estimates
Are you a trade? Get more work today!
Find out just how much a mansard loft conversion costs!
In this guide, we're going to explore everything you need to know about mansard loft conversion costs, the different types of loft conversions available and all the costs associated with these types of jobs.
On average, it will cost approximately £67,500 for a mansard loft conversion.
Ready to get a quote?
MyJobQuote has a Trustpilot score of 4.8 (39,000+ reviews) and is used by more than 1 million homeowners across the UK every year.
Tell us a bit about what you're after and we'll connect you with loft conversion specialists near you. They'll provide you with free, no obligation quotes for this type of job.
Want to find out more before you start comparing prices?
Take a look at the full guide below!
£67,500
Table of Contents
- How Much Does a Mansard Loft Conversion Cost?
- How Much Does Labour for a Mansard Conversion Cost?
- What Is the Cost of Mansard Loft Conversion Materials?
- Additional Mansard Loft Conversion Costs
- How Long Does a Mansard Loft Conversion Take?
- Mansard Roof Extension Cost Factors
- What's Involved in Building a Mansard Loft Conversion?
- Building Regulations & Planning Permission for a Mansard Loft Conversion
- Types of Mansard Loft Conversions
- Checklist: Hiring Contractors to Build a Mansard Loft Conversion
- FAQs
How Much Does a Mansard Loft Conversion Cost?
A mansard loft conversion can often cost between £55,000 to £80,000 (and potentially in the region of £70,000 to £90,000 for high-cost locations such as central London). Of course, the overall cost will be influenced by the quality of construction, fittings, and the complexity of the installation.
For example, if a bathroom is added, services for electricity and plumbing will need to be rerouted, with the costs for this additional work increasing the overall price of the project.
Mansard loft conversions are typically one of the more expensive loft conversion options compared to a dormer or hip-to-gable conversion.
Mansard Loft Conversion Prices
In the table below, you'll find a comparison of how much different types of loft conversion cost in the UK for different-sized spaces.
| Size | 30m² | 40m² | 50m² |
|---|---|---|---|
| Mansard | £30,000-£45,000 | £40,000-£60,000 | £50,000-£75,000 |
| Dormer | £20,000-£30,000 | £25,000-£40,000 | £30,000-£50,000 |
| Gable | £20,000-£36,000 | £28,000-£48,000 | £35,000-£60,000 |
| Velux | £12,000-£18,000 | £15,000-£25,000 | £18,000-£30,000 |
Want a custom price?
Post your job
As this table shows, the typical hip-to-gable loft conversion cost and the price of a dormer loft conversion are significantly less than a mansard conversion.
For more information on different types of loft conversions, our loft conversion cost guide covers the different options in more depth.
Is having a mansard roofed attic converted a particularly expensive job? Would this type of loft conversion cost more?
"There is a considerable amount of structural work involved. For this reason, mansard loft conversions are typically more expensive than other types of loft conversions.
Two deciding factors are the size of the property (i.e., whether it's a small terrace house or a large detached property) and the quality of the finish that you want (particularly any extras such as if the conversion includes adding a bathroom)."
Two deciding factors are the size of the property (i.e., whether it's a small terrace house or a large detached property) and the quality of the finish that you want (particularly any extras such as if the conversion includes adding a bathroom)."
How Much Does Labour for a Mansard Conversion Cost?
Because of the significant structural changes to the existing roof, mansard loft conversions are fairly labour-intensive projects. As a result, the labour costs for this type of extension can account for 40% to 50% of the total project budget.
With average mansard loft extension costs of £67,500, this means typical labour costs are likely to be in the range of approximately £27,000 to £34,000.
The table below shows how these labour costs are split between the different trades involved in installing a mansard loft conversion.
Estimated Labour Cost Breakdown
| Trade / Cost Area | Estimated Cost | Typical Time Required |
|---|---|---|
| Architect / Structural Calculations | £700-£1,000 | Several days |
| Scaffolding | £4,500-£7,500 | 6-8 weeks |
| Carpentry & Structural Work | £14,000-£18,000 | 4-6 weeks |
| Electrical Work | £1,200-£2,500 | 3-10 days |
| Plumbing | £1,200-£2,700 | 3-10 days |
| Plastering | £1,500-£3,000 | 1-2 weeks |
| Tiling | £300-£1,250 | 2-5 days |
| Decorating | £1,000-£2,000 | 1-2 weeks |
Want a custom price?
Post your job
Typical Trade Rates
If you use a specialist loft conversion company they will probably quote a single price for all the trades they would provide, but if you are wanting to hire each trade individually, the table below gives you an idea of the typical rates for each.
| Trade | Typical Rate |
|---|---|
| Architect / Structural | £700-£1,000 per project |
| Scaffolding | £750-£1,100 per week |
| Carpenter | £130-£200 per day |
| Electrician | £150-£250 per day |
| Plumber | £150-£270 per day |
| Plasterer | £150-£250 per day |
| Tiler | £140-£250 per day |
| Decorator | £120-£200 per day |
Want a custom price?
Post your job
The actual labour costs for your project are likely to vary depending on your location, size and complexity of the project, and your choice of finish, but these figures will give you a good guide.
What Is the Cost of Mansard Loft Conversion Materials?
Do you want to save money on your loft conversion? You could think about buying the materials yourself from a supplier. This section will cover the various supply costs for constructing a mansard loft conversion in your home.
Structural Timber & Joist Prices
Structural timber and joists are one of the most important materials in your mansard loft conversion, creating the framework and providing a solid, load-bearing floor structure. How much timber you need will depend on your existing roof structure and the size of your conversion.
Expect to pay between £10 and £30 per metre for timber joists, although the larger structural timbers you will need can cost considerably more depending on the dimensions and specs required. Because of this timber is usually the most significant material cost for your loft conversion project.
Steel Beam (RSJ) Prices
Steel beams, or RSJs (Rolled Steel Joists), are usually required for most mansard loft conversions. These beams provide additional structural support and help carry the weight of the new floor, internal walls, and any roof alterations.
The cost will depend on the size of the beam required and its load-bearing capabilities but expect to pay between £800 and £2,500 for each RSJ, with larger projects often requiring multiple beams.
Roof Covering Prices
You will probably need to replace some or all of your existing roof covering as part of your mansard loft conversion. The cost will depend on the quantity and quality of the material chosen, with more durable, better-looking materials often having a higher price.
Concrete roof tiles are an affordable option at around £15 to £30 per m², whereas natural slate will cost between £40 and £80 per m². Man-made slate is an attractive but cheaper option at between £20 and £40 per m².
Insulation Prices
Building Regulations mean there are minimum thermal efficiency standards your new loft conversion will have to meet, which makes insulation one of the most important construction materials. The design of your conversion and the thermal efficiency levels you're trying to achieve will affect the type and thickness of insulation you need.
Expect to pay between £5 and £15 per m² for mineral wool insulation, and between £15 and £35 per m² for rigid insulation boards, although more expensive, better-performing insulation boards are sometimes used if space is limited.
Windows Prices
The price of loft conversion windows will differ depending on your style. If you are building a dormer loft conversion, you must consider the cost of dormer windows. Smaller dormers are normally priced at £150, while new window costs for bigger dormers can cost at least £300 per window.
Roof lights are another common loft conversion window design. These are slightly more expensive, ranging from £320 to £550. However, they contribute to the creation of a modern and airy living space and greatly improve the aesthetic.
Staircase Prices
Your new loft conversion will need a staircase to provide safe and easy access. The cost will depend on the size, materials used, the layout, and whether you want it to have a bespoke design.
A standard softwood staircase should cost between £500 and £1,500, and you should expect to pay between £1,500 and £4,000 for a hardwood staircase. Your staircase could cost considerably more, however, if you opt for a bespoke designed option.
Loft Flooring Prices
Flooring for your loft transformation is one of its most important costs. The cost of loft conversion flooring varies depending on the material used. Vinyl flooring, for example, costs about £6 to £14 per m², whereas laminate costs between £7 and £25 per m².
Hardwood is another popular loft conversion flooring option, ranging from £35 to £45 per m². If you want carpet for your loft conversion, you could perhaps budget between £5 and £30 per m².
Heating Prices
To ensure that your loft conversion is properly heated, installing central heating is one option, or you could potentially remove and replace a radiator from elsewhere if that's a more viable option. A standard horizontal or vertical radiator costs between £50 and £900, even as electrical radiators cost between £90 and £400.
Underfloor heating is more expensive, and it must be installed before your flooring can be installed. Wet underfloor heating typically costs between £60 and £80 per m². The floor is heated by pumping water through pipes.
The second alternative is dry underfloor heating, which typically costs between £30 and £40 per square metre. This includes electric mats and wires connected to the main power supply to heat the floor.
Loft Lighting Prices
Loft spaces prior to being converted aren't usually the brightest area in the house, as such installing light fittings is going to be an important job.
Ceiling lights could be included and are an ideal solution. These start at £7 and can cost up to £4,000 if you want something more luxurious.
Lamps are another popular type of lighting. Table lamps typically cost between £3 and £1,000, while floor lamps cost between £12 and £1,800.
Smart lighting is one of the more advanced lighting options. These can be managed by a smart device and help you save money on energy while also lowering your carbon footprint. Smart lightbulbs range in price from £15 to £170.
Additional Mansard Loft Conversion Costs
A mansard loft conversion is typically larger than other loft conversions, and it can add nearly an entirely new storey to the building.
As a result, you may want to make additional improvements to the rest of the property. This section will discuss the additional costs that may be incurred because of adding a mansard conversion to your home.
Architect Cost
Not all contractors will require architect plans to complete a mansard loft conversion. However, making plans is still a good idea. It ensures that everyone stays on the same page throughout the project.
Architect prices are around £400 for a basic set of plans, but you can expect to pay up to £1,500 for more detailed plans that highlight the full scope of the work.
Given the project's cost, this is not a large sum, but it can significantly improve results. Another benefit of hiring an architect to create detailed plans is that it prevents you from making up your mind later, saving you money in the long run.
Planning Permission Costs
A mansard loft conversion may require require planning permission, more so than other types of conversion because of the significant changes to the roof shape. Planning permission is probably not included in the quotes you receive, so expect to pay for the application fee and the cost of any supporting drawings.
Expect to pay between £250 and £350 for your planning application, although some local authorities charge more, and the cost of any required drawings or additional planning support could add several hundred pounds more, depending on the complexity of your project.
Party Wall Surveyor Costs
If your mansard loft conversion is on a terraced or semi-detached home, as the work will affect the shared wall between yours and your neighbours' property, a party wall agreement will probably be required.
This can be something you can arrange yourself, but if you need to appoint a party wall surveyor you could expect to pay between £700 and £1,500. These costs can be higher if you are dealing with two sets of neighbours, or your neighbours appoint their own party wall surveyor.
Structural Engineer Costs
Mansard loft conversions typically involve significant structural solutions, and you may require a structural engineer to calculate beam sizes and load-bearing requirements to help ensure the conversion complies with building regulations.
This specialist professional service may not be included in your loft conversion quote, in which case you can expect an additional cost in the region of £500 to £1,500 depending on the complexity of the project.
Skip Hire Cost
Of course, a skip, or several skips, will be required when you're getting a loft conversion done.
The tradesperson or team that you hire to complete a loft conversion will likely have a skip hire company that they work with — and may have negotiated lower rates if you let them handle it.
The cost of skip hire, if you wanted to handle it yourself, would be around £200 to £300 per week.
Keep in mind: A skip licence is required if the skip will be placed on the road instead of the driveway or in the garden. This licence must be renewed daily, and the local council determines the cost.
House Painting Cost
The cost of painting a house exterior that's a two-storey, three-bedroom house is around £850 in the UK. However, keep in mind that this is only an estimate, and many cost-variable factors will affect the final cost of your project.
These factors include the size of your home, its design, the materials used, and the tradesperson's daily or hourly rates.
How Long Does a Mansard Loft Conversion Take?
The amount of time spent constructing your loft conversion is important to consider because it will significantly impact the final cost. The longer the job takes, the higher the cost.
While we have based this guide on the average mansard loft conversion taking around 6 to 8 weeks for a basic project, there are a number of factors that can influence each individual situation. This may include more complex builds such as installing an ensuite bathroom, and adverse weather conditions may cause some work to be put on hold.
The size of your space will determine the length of time required and if you have a larger, or more complex, loft conversion then it's not uncommon for the project to take up to 12 weeks in total.
In some cases, such as if planning permission is required for proposed work on a listed building, there can be delays to ensure any relevant paperwork is signed off and approved.
Ask a Trade
Got a question that only a tradesperson can answer? We have thousands of trades ready to answer any question you may have.
Ask your question
Mansard Roof Extension Cost Factors
The price of a mansard loft conversion can vary significantly depending on the size, layout, and location of your property, and the specification you choose for the fixtures and fittings. Other factors such as structural work, planning and building regulations requirements, adding bathrooms, and upgrading heating systems can all increase the cost of your mansard loft conversion.
Finishing Quality
The materials used in the construction and fit-out of a mansard roof loft conversion would significantly impact the cost. While some materials will be needed to meet specific Building Regulations standards, others will be a matter of preference or budget. Quite often, the option of roof covering is dictated in this manner.
While it may be necessary to adhere to either tiles or slate to maintain the consistency of a street, there is quality and thus price differences available. The price, quality, and durability of man-made slates versus natural slates, for example, will differ.
Location
The cost of a mansard dormer is also affected by the location of your property. For example, labour and material costs will be higher in London and the country's southeast, while prices elsewhere in the UK may be lower.
It may be necessary to commission a bat survey in rural areas because disturbing or disrupting bat habitats is prohibited. A bat survey can cost between £300 and £1,000, depending on whether it is preliminary or comprehensive.
Roof Tiles Type
Suppose the conversion entails replacing the roof, the type of tiles matters because some will almost certainly have to be changed as part of the construction. In addition, converting houses with slate tiles is typically more expensive than converting houses with concrete tiles.
Loft Conversion Dimensions
As you may expect, a larger loft space is likely to be more expensive than a small and straightforward conversion. However, it's not just the overall dimensions that impact the cost. For example, if you're looking to convert an area with an unconventional shape, the dimensions and angles will also affect how much work is involved.
Structural Changes
Because a mansard loft conversion includes changing the full sloping face of the roof to a steep angle (at least 72 degrees), structural changes to the entire roof are required. Typically, the larger your home, the higher these costs, but the complexity of the structural alterations can also have a significant impact on the price.
Interior Walls
If you decide to divide your new loft space into multiple rooms, the cost of the extra walls must be factored in. It will cost around £850 to install a stud wall and plaster.
What's Involved in Building a Mansard Loft Conversion?
Mansard loft conversions are not considered suitable for a DIY project. This is partly due to requiring a significant amount of structural work to be carried out, along with the complexities involved to ensure the building is safe and meets all the necessary building regulations.
There are several stages involved in completing a mansard loft conversion, so it isn't a straightforward job to attempt by yourself. An architect, architectural technician, or surveyor will need to draw up plans for your conversion, and due to the scope of work involved you may also require planning permission (even though this isn't usually required for other types of loft conversions).
It is always recommended to request at least three quotes from companies that specialise in loft conversions to ensure you are receiving a good price. With MyJobQuote you can find local tradesmen for a fast, free quote with no obligation to take it any further.
Below is a broad overview of the process involved when building a mansard loft conversion:
Before the Job Starts
- Planning and Design — An architect, architectural technician, or surveyor prepares detailed plans outlining all structural changes required for the mansard loft conversion —
- Planning Permission — An application is submitted to the local authority planning department, and approval must be granted before work can begin.
- Scaffolding and Preparation — Scaffolding is erected and materials are delivered to site in preparation for opening the roof.
During the Job
- Opening the Roof — The roof is opened to begin construction of the mansard structure.
- Structural Changes and Windows — Major structural alterations are carried out, including installing supports and fitting roof light windows.
- External Work. The roof structure is completed, tiles are replaced and finished, roof insulation is installed, and preparations begin for plumbing and electrical installations —
- Floors and Walls — Remaining windows are installed, flooring is laid with proper ventilation, and plasterboard and internal walls are fitted.
- Electricals and Interiors — The staircase is installed, electrical work is completed, bathroom fittings (if applicable) are added, doors are hung, plastering is skimmed, and skirting boards are installed.
After the Job
- Finishing Touches — Any remaining tasks are completed, interior decorating begins if included in the contract, and final details are addressed.
- Project Completion — Scaffolding is dismantled and the mansard loft conversion is finalised.
A mansard loft conversion would give us the extra space we need but I think they can look a bit boxy and ugly. What would you suggest we consider to make a conversion look more attractive?
"A mansard loft can look amazing with dormer inserts and a parapet wall. Using the right roof covering, such as slates, combined with leaded dormers, can significantly enhance the aesthetic appeal."
Building Regulations & Planning Permission for a Mansard Loft Conversion
A mansard loft conversion usually falls under Permitted Development rights, meaning planning permission may not always be required, although this isn't always the case as explained below.
Planning Permission
In most cases, unless you are significantly changing the appearance of your property, a mansard loft conversion can be completed under Permitted Development rights, so you won't need to apply for planning permission.
Exceptions include properties that are listed buildings, or if you live in a protected area such as a conservation area or national park. You may also need permission if installing a front-facing window that overlooks a main road.
If in doubt, speak to your local planning authority for clarification. If you do need to apply, this typically costs around £200 (prices vary by location) and can take 8–13 weeks for approval or rejection.
Building Regulations
Building regulations are required to ensure loft conversions are safe, structurally sound, energy efficient, and compliant with fire protection standards.
Your local Building Control Department or a privately approved inspector can review progress to ensure standards are met. They will issue a completion certificate at the end, with costs ranging from £350 to £1,250 depending on the complexity of the conversion.
If you live in a semi-detached or terraced property, you may also need a Party Wall Notice to inform your neighbour of work being carried out. Surveyor fees can range from £150 to £200 per hour, with total costs often around £1,000.
Are double mansard loft conversions structurally strong? And are they durable or high maintenance?
"Double Mansard loft conversions are structurally sound and durable if constructed correctly using large-sized structural timbers with normal spacing centres. It's advisable to have a structural engineer provide a design and calculation report. Maintenance is generally low, as this type of loft forms part of the building’s structure and is typically covered with roof tiles and lead, ensuring a long lifespan with minimal upkeep."
Types of Mansard Loft Conversions
A mansard conversion is typically built at the back of your property and has a horizontal roof with a nearly vertical 72-degree back wall. This creates a large amount of loft space and ensures that the proportions of the room are desirable.
Most house types can accommodate this type of loft conversion, so a mansard roof loft conversion is an option if you have a terraced, semi-detached, or detached home. However, the design specification will vary depending on the property type, affecting the cost.
Windows in a Mansard are typically housed in a box-shaped Dormer that slightly projects internal space and allows natural sunlight to flood in.
Furthermore, because the windows are vertically oriented outwards, the Mansard loft conversion appears to have always been a part of your home. This section will discuss the various types of mansard loft conversions and their benefits and drawbacks.
L-Shaped Mansard Loft Conversion
An L-shaped mansard loft conversion is when two roof structures are built in such a way that they connect. Typically, one is built on the rear outrigger roof and the other on the main roof, giving it the instantly recognisable L-shape.
Because of the shape, L-shaped mansard loft conversions are only suitable for certain properties, primarily Edwardian or Victorian properties with an existing addition at the back known as a two-storey outrigger. This construction style is a great way to get more space out of a property, especially if you own a mid-terrace property.
Pros
- ✔ Great way to add space
- ✔ Blends into a home
Cons
- ✖ Not suitable for every home
Double Mansard Loft Conversion
A double Mansard loft conversion is also available, similar to the standard Mansard conversion. The distinction is that it includes a Mansard on the front side of the property. This sort of loft conversion is prohibited in some jurisdictions.
This type of Mansard roof loft conversion is like a regular Mansard loft conversion, but it includes a Mansard towards the front of the property. These loft conversions are subject to planning restrictions in some parts of the country.
Pros
- ✔ Popular choice
- ✔ Adds value to a home
Cons
- ✖ Need planning permission
Checklist: Hiring Contractors to Build a Mansard Loft Conversion
The significance of bringing on the right builder cannot be overstated. It will result in the highest quality build, but having a good partnership with your builder will make sure you get exactly what you want while possibly saving you time and money.
But where do you find such a builder? Use our checklist to find the best contractor for your loft conversion.
- Locate a builder in your area — Finding a local builder can be extremely beneficial when it comes to your construction. Time on site, knowledge of local planning permission, builders' merchants, and other local trades are invaluable nuggets of information that you'll appreciate on-site. In addition, there's no harm in going for a walk around your neighbourhood or taking a short drive around the neighbourhood to see if any construction projects are going on. It will give you an idea of the builders who are active in your area, and if you see a builder's board, it is a sign that, at the very least, this is a builder who is proud of their work and looking for more.
- Get recommendations — Many trades rely on word of mouth, and if you can find a builder through someone you trust, whose work you can go see, you can decide whether they'll do a good job.
- Speak with previous customers — Don't be afraid to ask for a list of previous customers; if they're confident they've done a good job, they should be happy to provide details. This will provide you with an excellent opportunity to learn more about them and see examples of their work first-hand. Meeting previous customers is a great way to learn about the quality of a builder's work and other important factors.
FAQs
Is a mansard loft conversion better than a dormer loft conversion?
In general, a mansard conversion will provide more space above head height, but if you're looking to convert on a price limit, a dormer will provide plenty of usable space for a bedroom, and possibly even an en-suite, at a slightly lower cost.
How much headroom does a mansard loft conversion provide?
A standard mansard loft conversion typically provides around 2.2m-2.5m headroom. As such providing a higher ceiling than that of a traditional dormer or Velux conversion, however, exact measurements may vary depending on the individual project.
How energy-efficient is a mansard loft conversion?
Provided the conversion has been sufficiently insulated, they can prove very energy-efficient. Modern lofts often include roof insulation, double-glazed windows, and airtight finishes, which help maintain temperature and reduce heating bills.
Can a mansard loft conversion be added to a bungalow?
Yes, it is possible to install a mansard loft conversion in a bungalow. However, it may require raising the roof or modifying the roof structure to create enough headroom. As with any loft conversion, proper planning and structural work is essential, but it can provide additional living space in return.
Is it worth building a mansard loft conversion?
According to recent Nationwide Building Society research, converting a loft space can increase the value of your home by up to 20%. This increase can be significant in areas where average house prices are high. Your house value increase may also be influenced by broader construction trends. Check out the latest construction statistics, which offers insights into these trends.
