What Is a Mansard Loft Conversion? A Complete Beginner’s Guide

A Mansard loft conversion is a sophisticated and highly effective method of extending a property by creating a full additional floor of living space. This type of conversion derives its name from the 17th-century French architect François Mansart, who popularised the style. Today, it is particularly common in built-up urban areas, especially in cities like London, where space is at a premium and planning regulations often limit the scope for rear or side extensions.

The defining feature of a Mansard loft conversion is the construction of a flat roof with the rear roof slope altered to a steep angle—typically around 70 degrees from horizontal. This steep pitch, combined with the inclusion of dormer-style windows set vertically into the slope, creates a near-vertical rear façade. The result is a loft conversion that provides significantly more internal volume and head height than other types of conversions, such as Velux (rooflight) or standard dormer styles.

One of the key advantages of the Mansard design is its ability to transform what is often an underutilised attic into a spacious and functional new room or set of rooms. Whether used as a master bedroom with en-suite, a home office, a guest suite, or even a self-contained flat, the possibilities are considerable. The increased floor-to-ceiling height and improved natural light also make it an attractive option from both an aesthetic and practical standpoint.

However, the benefits come with added complexity. Because a Mansard conversion involves a significant alteration to the roof’s shape and often affects the front or rear elevation of a property, it almost always requires planning permission. This is particularly important to consider in conservation areas or on listed buildings, where additional scrutiny may apply. The process typically involves working with an architect to produce detailed drawings and liaising with the local planning authority for approval.

In summary, a Mansard loft conversion is an ambitious yet rewarding home improvement project. It can dramatically increase both the liveable space and market value of a property, while offering a stylish architectural solution that integrates well with a wide range of property types.

The Mansard loft conversion is distinct in both form and function, offering homeowners one of the most transformative options available when it comes to expanding their property. While it requires more structural intervention than simpler loft styles, the design features of a Mansard conversion make it an attractive investment, both in terms of aesthetics and liveable space.

One of the defining characteristics of a Mansard loft is its rear roof slope. Unlike the standard angled pitch found in most traditional roofs, the Mansard design replaces this with a steep incline, typically set at 70 degrees. This near-vertical rear elevation maximises internal headroom across the entire width of the loft, turning previously unusable attic corners into functional, comfortable living space. In many cases, this creates a full additional storey that feels fully integrated with the existing home.

The structure is capped with a flat roof, often subtly pitched to allow for drainage but appearing level from the street. This flat roof design not only contributes to the clean, boxy aesthetic of a Mansard extension but also allows for the potential installation of roof-lights or even solar panels, depending on orientation and planning constraints.

Windows in a Mansard conversion are typically set vertically into the steep rear slope, offering a modern twist on the classic dormer. These can range from simple, functional casement windows to Juliet balconies with glazed doors, which are increasingly popular in contemporary loft designs. In conservation areas, timber-framed sash windows may be used to complement the architectural character of neighbouring properties, helping to ensure planning compliance.

Internally, the space created by a Mansard conversion is often significantly more generous than other types of loft conversions. The full-height walls on the rear side allow for the comfortable placement of furniture, fitted wardrobes, and even full en-suite bathrooms, which may not be possible with other styles due to restricted ceiling height.

Another notable feature of the Mansard design is its versatility. It can be adapted to a variety of property types, including terraced houses, semi-detached properties, and even some detached homes. While commonly constructed to the rear of the property, Mansard extensions can also be applied to the front elevation or wrapped around the side in what is known as an L-shaped Mansard — ideal for creating multiple rooms or larger open-plan layouts.

The result is a spacious, well-lit, and highly functional addition to a home, with architectural appeal that can enhance both lifestyle and property value. When designed sensitively and in keeping with the existing character of the building, a Mansard loft conversion becomes a seamless and valuable part of the overall structure.

When considering a loft conversion, homeowners are often presented with several options—each with distinct advantages, limitations, and implications for planning and design. Among these, the Mansard loft conversion is frequently compared to more common alternatives such as dormer, Velux (rooflight), and hip-to-gable conversions. Understanding the differences between these styles is key to choosing the right solution for your property, budget, and long-term goals.

Mansard vs Dormer

The most common comparison is between the Mansard and the dormer conversion, as both extend usable space by altering the roof structure. A dormer conversion typically involves constructing a box-like extension that projects vertically from the existing roof slope, usually at the rear of the house. This adds additional floor space and head height in a limited portion of the loft, while leaving the rest of the roof intact. Dormers are often simpler to construct, may fall under permitted development rights, and are generally more cost-effective than Mansard conversions.

However, a Mansard conversion goes significantly further. Rather than adding a projection, it transforms the entire rear roof slope into a steeply pitched wall, essentially creating a full additional storey. This not only results in more consistent ceiling height and floor space but also delivers a more seamless and integrated feel. While dormers can appear as add-ons, a well-designed Mansard can look like a natural extension of the original architecture.

Mansard vs Velux (Rooflight) Conversions

A Velux or rooflight conversion is the least invasive and most affordable loft conversion option. It involves minimal structural alteration—typically just the installation of skylight windows into the existing roof slope. These conversions rely on the original roof shape and are best suited for properties with ample existing loft height.

In contrast, a Mansard conversion is a complete structural overhaul. While Velux conversions are ideal for light-touch renovations or for properties in conservation areas with strict planning limits, a Mansard offers much greater flexibility in terms of layout and function. If the existing loft space is limited in head height or shape, Velux conversions may simply not be viable.

Mansard vs Hip-to-Gable Conversions

A hip-to-gable conversion is primarily applicable to semi-detached or end-of-terrace properties with a hipped (sloped) roof. This style involves straightening the sloping side of the roof to form a vertical gable, thereby increasing internal space. It is often combined with a rear dormer for maximum benefit.

While hip-to-gable conversions offer a modest increase in space and preserve much of the original roofline, they still fall short of the dramatic spatial transformation afforded by a Mansard. In fact, it is not uncommon to combine both—extending the side wall with a hip-to-gable and then constructing a rear Mansard to maximise floor area.



Each of these loft conversion styles serves a specific purpose and is suited to different architectural conditions. The choice ultimately depends on the goals of the project, the structural possibilities of the property, and the extent to which the homeowner wishes to expand and reconfigure the available space.

Choosing the right type of loft conversion for your home can be a daunting task, particularly with the range of options available and the various factors that need to be considered, such as planning permission, budget, and design requirements. Whether you're certain that a Mansard loft conversion is the best solution or if you're still unsure about the most suitable option for your property, our expert team is here to help.

At [Your Architecture Practice Name], we specialise in tailored design solutions for loft conversions, ensuring that every project reflects the unique character of your home while maximising its potential. From initial consultation to planning and execution, we guide you through every stage of the process. We’ll help you understand the pros and cons of Mansard, dormer, Velux, or hip-to-gable conversions and provide personalised advice based on your space, requirements, and budget.

If you're ready to explore the potential of your loft space or would simply like expert advice on what’s possible for your property.