Mansard Loft Conversion


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A Mansard loft conversion is a popular type of home renovation that maximises the available space in your loft. Named after the 17th-century French architect François Mansart, this conversion style is characterised by a flat roof and a back wall slope inward at an angle of 72 degrees. The windows are typically housed within small dormers, giving the loft conversion a unique aesthetic appeal.

This type of loft conversion is often more complex and time-consuming than other types, such as dormer or hip-to-gable conversions. However, the result is a spacious and light-filled room that blends seamlessly with the rest of the house, making it an attractive option for homeowners.

mansard loft london


Determining the suitability of your home for a Mansard loft conversion involves considering several key factors. The structural integrity and design of your property, the available loft space, and local planning regulations all play a significant role in this assessment.

The existing loft space is a crucial consideration. A Mansard conversion requires a certain amount of head height to ensure the new space is comfortable and functional. A minimum height of 2.2 metres is generally recommended. If your loft space doesn’t currently meet this requirement, certain adjustments, such as lowering the ceilings of the rooms below, may be necessary.

Local planning regulations can also influence the feasibility of a Mansard conversion. Some areas, particularly conservation areas, may have restrictions on the type of alterations you can make to your property.

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Mansard loft conversions come in different types, each offering unique features and benefits. The two main types are the standard Mansard and the L-shaped Mansard.

Standard Mansard Loft Conversion: This is the most common type of Mansard conversion. It involves modifying one or both sides of the roof to create a flat roof and steeply sloped walls. This type of conversion is suitable for most property types and offers a significant increase in living space.

L-Shaped Mansard Loft Conversion: This type of conversion is typically suitable for properties with an existing back addition, such as a kitchen or bathroom extension. The L-shaped Mansard conversion extends over this back addition, creating an ‘L’ shape when viewed from above. This type of conversion offers even more space and is particularly popular for terraced houses.


Choosing a Mansard loft conversion comes with a host of benefits that make it a popular choice among homeowners. Here are some of the key advantages:

Increased Living Space: Mansard conversions effectively utilise the loft space, providing additional room that can be used as a bedroom, office, or entertainment area.
Property Value Boost: By adding extra living space, a Mansard conversion can significantly increase the value of your property, making it a wise investment.
Design Flexibility: The unique structure of a Mansard conversion allows for greater flexibility in design and layout, enabling you to customise the space to your specific needs and preferences.
Natural Light: The inclusion of dormer windows in a Mansard conversion ensures ample natural light, creating a bright and airy space.

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Planning permission is a critical aspect to consider when planning a Mansard loft conversion. While some loft conversions fall under ‘Permitted Development’ rights and do not require planning permission, this is not always the case for Mansard conversions due to their more significant structural changes.

In general, Mansard conversions often require planning permission due to the alterations to the roof shape and structure. However, this can vary depending on your location and the specific rules of your local planning authority.

If your property is in a conservation area or is a listed building, you will likely need to apply for planning permission. It’s also important to note that even if your conversion does fall under Permitted Development, you may still wish to apply for a Lawful Development Certificate. This certificate is not the same as planning permission but serves as proof that your conversion is lawful, which can be beneficial when selling your property.

Always consult with your local planning authority or a planning professional before proceeding with a Mansard loft conversion to ensure you comply with all necessary regulations and requirements.


The cost of a Mansard loft conversion in London can vary significantly based on several factors. These include the size and structure of your loft, the complexity of the design, the materials used, and whether any additional modifications to your property are required.

While it’s difficult to provide an exact figure without a detailed assessment of your property, it’s important to note that Mansard conversions are typically more expensive than other types of loft conversions due to the extensive structural changes involved.

Despite the higher initial cost, a Mansard loft conversion can be a worthwhile investment. The significant increase in living space can greatly enhance your property’s value, often covering the cost of the conversion in the long term.

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One of the greatest advantages of a Mansard loft conversion is its versatility. The additional space can be tailored to your specific needs, whether that’s a home office, a games room, or a cinema room.

Home Office: With more people working from home than ever before, a quiet, dedicated workspace has become a necessity for many. A Mansard conversion can provide the perfect solution, offering a separate area away from the hustle and bustle of the rest of the house.

Games Room: Whether you’re a gaming enthusiast or have children who need their own play space, a Mansard conversion can be transformed into the ultimate games room. The ample space and potential for soundproofing make it ideal for this purpose.

Cinema Room: Imagine having your own private cinema at home. A Mansard conversion provides enough space to house a large screen, comfortable seating, and even a popcorn machine for the ultimate movie night experience.

The possibilities are endless with a Mansard loft conversion. Whatever your needs or lifestyle, this type of conversion can provide the extra space you need to enhance your home and lifestyle.


Mansard loft conversions are not just practical; they also offer significant architectural appeal. The distinctive design, characterised by a flat roof and inward sloping walls, adds a touch of elegance and sophistication to any property. The small dormer windows typically used in Mansard conversions contribute to this aesthetic appeal, providing a unique and attractive exterior that stands out from traditional loft conversions.


When planning a Mansard loft conversion, it’s essential to consider energy efficiency. The design and construction of the conversion can significantly impact the thermal performance of your home. Proper insulation is crucial to prevent heat loss, reduce energy bills, and create a comfortable living environment. Additionally, choosing energy-efficient windows can further enhance the energy performance of your Mansard conversion.

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One of the key benefits of a Mansard loft conversion is the additional space it provides. However, to make the most of this space, effective storage solutions are essential. Built-in storage, such as a loft walk in wardrobe, can be integrated into the design of the conversion, providing practical storage without compromising on living space. Additionally, the unique shape of a Mansard conversion offers opportunities for creative storage solutions, such as under-eaves storage.


A Mansard loft conversion is not just a short-term solution for space issues; it’s also a way to future-proof your home. Whether your family is growing, or you need more space for hobbies or work, a Mansard conversion provides the flexibility to adapt to your changing needs. Furthermore, the added value that a Mansard conversion brings to your property makes it a sound investment for the future.


Mansard loft conversions are often very cost-effective and simple to construct, yet another bonus of this particular option, and are suited to a number of style properties too. From detached to semi-detached, terraced to chalets and even bungalows, these typically are all suitable for Mansard loft conversions. 

Of course, having an expert take a look to give you the thumbs up is the only way you’ll know and thankfully, here at Clapham Construction Service, we offer a free, no-obligation consultation. If you’d like to book one of our complimentary consultations, please don’t hesitate to contact us today on 0203 950 7957. Our team of loft specialists will be only too happy to help, offering as much advice and guidance as you need to make the most informed decision possible.

Have your say…


Nicholas Carpenter
Nicholas Carpenter
Clapham Construction have done a great job on our loft conversion and we are very pleased with how smoothly the project went, and the brilliant loft space that we now have. Paul - thank you especially for guiding us through all the stages before and during the build. Their workmen were hard working from start to finish, efficient, and obviously very skilled. They were also polite, helpful and really tidy. We had great communication by email with their office, and with Paul in person and on the WhatsApp group - thank you. Our family in USA are now looking forward to staying with us in comfort this summer and beyond!
Bianca Hamilton
Bianca Hamilton
Paul, Dangis and the team are simply top notch. They did such a high-quality job on a tight timeframe and communicated so well throughout. They were a pleasure to work with, handled all elements of the build from start to finish and kept disruption as minimal as they could. Couldn’t recommend them more highly if I tried.
Mindy Lee
Mindy Lee
Thank you Clapham Construction! Your team were friendly, efficient, and highly motivated. The project ran to schedule with effective overlapping of tasks to allow for minimum disruption. Paul kept us actively involved at each stage of the process, so we always knew what was happening when, which was really reassuring. If we ever had a question, he would talk it through with us in person and offer advice without any pressure or expectation. The work is completed to an excellent standard. All the construction workers where kind, considerate, friendly, polite and kept our house as clean and tidy as possible. This took so much of the stress out of living on site during the works with a young son. Even the neighbours commented on how polite and considerate the builders had been. We would highly recommend this team for anyone thinking of undertaking a loft conversion in the future.
Shayan Bokhari
Shayan Bokhari
Paul, Dangis and their team were excellent given we had some obstacles with the council on design, they accommodated what we required. The work was very professional and communication was on point. We are very happy with our end result and any teething issues they resolved quickl. I would recommend the team to anyone. Thanks again for all your hard work.
Laila A
Laila A
Really lovely team - all professional, friendly and was great to have Dangis and Paul popping in regularly and being on the ball with the project. Happy with our new loft, all work done to an excellence standard, any follow up questions or issues dealt with quickly. Would highly recommend. Thank you very much.
Dani Carter
Dani Carter
Absolute professionals is the first thing that comes to mind when I think of Clapham Construction service. And there are two further things you need to know about them: they are brilliant at what they do and they are generous in spirit. Throughout our project Paul and Dangis answered our naive questions with warmth and care. They helped guide us at every turn, and almost certainly saved us money by making sure we considered all the options we had before making key decisions. But not just customer care, the building work is also top notch. The build itself was a well oiled process, coordinated with skill. I was initially worried about getting an anonymous loft company I'd never heard of in (after getting 8 different quotes from a variety of places including famous local ones) and being part of the 'box on the roof' brigade. Yet somehow, they have created build magic with some tweaks on 'a little bit of height' here, and 'a little configuration' there. We keep marvelling at the sturdiness and smoothness of the physical build even now, and the army of highly skilled teams they have were a pleasure to host in the house while we worked from home. And finally the most important bit - the money stuff- our Loft extension (including bathroom) was completed on time and more or less on budget. The additional costs were the unforseen - (yikes a victorian chimney needs dismantling!) and a few flourishes that we ourselves added to the mix - (can the door handles be gold?). Any additional build costs were communicated efficiently and immediately. Our experience of Clapham Construction is that they are patient, hugely knowledgable, and detail orientated with a wealth of incredible advice. Don't delay on getting them on your project!
Mikey Johns
Mikey Johns
We spoke to a few companies to quote our dormer loft conversion but were immediately impressed speaking to Dangis & Paul and went with Clapham CS. We’re really happy with the end result which has given us some much needed extra space. Progress was quick, these guys are very experienced and know exactly what they’re doing. They’ll talk you through your plans and give you honest advice at key stages when you need to make a decision, very patient with us too! Would definitely recommend, they’ve done numerous houses in our neighbouring streets too, end results always look great.
Maria Luisa McKendry
Maria Luisa McKendry
Highly recommend this company. As first time buyers and first time renovators we couldn't be happier with their service. Paul and Dangis are very professional and thorough, at no times does it feel like corners are cut. They are able to provide genuine advice and guidance while being accommodating ensuring a stress free process.
Stuart Williams
Stuart Williams
Clapham Construction completed our kitchen extension for us. We’re really pleased with the results, and it has changed the whole place. The price was agreed upfront and there were no hidden extras. Good communication throughout the whole process on WhatsApp and Dan showed great building experience. They had the whole team from build, kitchen fitting through to finishing the garden off available in house so made it a lot easier. Thanks guys.
Tom Forman
Tom Forman
We are delighted with our new loft conversion, Clapham Construction did a great job. They were highly professional, no hidden costs, and with friendly employees who treated the rest of the house with respect. We would not hesitate to recommend them.

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What is a mansard loft conversion?

A mansard loft conversion is a type of loft conversion that involves altering the structure of the roof to create a more box-like shape. This is achieved by steepening the angle of the roof sides to almost vertical and adding a flat roof on top.

Are mansard loft conversions suitable for all property types?

Mansard loft conversions are most commonly found on older, terraced properties, particularly in city environments. However, they can be applied to a variety of property types, including semi-detached and detached houses. It’s always best to consult with a loft conversion specialist to determine the most suitable type of conversion for your property.

What is the typical cost of a mansard loft conversion?

The cost of a mansard loft conversion can vary depending on the size, location, and specific requirements of the project. However, as they involve significant alterations to the roof structure, mansard conversions tend to be more expensive than other types of loft conversions. Costs can typically range from £40,000 to £70,000.

Do mansard loft conversions require planning permission?

Unlike some other types of loft conversions, mansard conversions often require planning permission, as they involve a significant change to the structure and appearance of the house. It’s always recommended to check with your local planning authority before proceeding with a mansard loft conversion.

What are the benefits of a mansard loft conversion?

Mansard loft conversions can offer several benefits. They provide a substantial amount of additional living space, as they effectively add an entire storey to your home. This can be used for extra bedrooms, bathrooms, or living areas. Mansard conversions also offer a high degree of flexibility in terms of interior layout and design, due to the large, flat walls and ceilings they create.

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