Mansard roof extensions on Redcliffe Road: A Guide to the New LDO
The recently introduced Royal Borough of Kensington and Chelsea Local Development Order (LDO) for Redcliffe Road in Chelsea presents an exciting opportunity for homeowners to improve and enlarge their properties with a mansard roof extension. This streamlined planning process is particularly valuable in conservation areas like Chelsea, where maintaining the historic character of streets is a priority.
We are currently working on an extension project in Chelsea which has been able to benefit from this new planning policy
What Is a Mansard Roof Extension?
A mansard roof extension is a type of loft conversion that adds an additional storey to a home. It features a roof with two pitches: a shallow upper slope and a much steeper lower slope, often with dormer windows integrated into the design. This style is commonly seen in grand Parisian buildings and London’s historic terraces, making it a highly sympathetic extension for period properties.
In Chelsea, mansard extensions are often the preferred method for increasing living space while maintaining the traditional aesthetic of terrace houses. Unlike other types of loft conversions, such as dormer or hip-to-gable conversions, a mansard extension offers a full extra floor, making it one of the most efficient ways to increase a home’s footprint.
Unlocking the Potential of Your Home with a Mansard Roof Extension
A mansard roof extension is one of the most effective ways to gain valuable additional living space in a period home. Whether you need an extra bedroom, a home office, or a more spacious living environment, a well-designed mansard extension enhances both the functionality and value of your property while blending seamlessly with the architectural character of Redcliffe Road.
As a specialist architecture practice with extensive experience in Chelsea, we understand the complexities of working in conservation areas. We are currently designing a mansard roof extension on Redcliffe Road, carefully balancing modern living needs with historic preservation.
In this blog, we explore what the LDO means for Chelsea homeowners, the benefits of working with an architect on a mansard roof extension, and how to navigate the conservation requirements of this historic area.
What Is a Local Development Order (LDO)?
A Local Development Order (LDO) is a planning tool that grants automatic approval for specific types of development within a defined area, provided they meet strict design and construction criteria. This means homeowners on a number of selected houses on Redcliffe Road can now extend their homes upwards without needing to go through a full planning application, as long as they adhere to the LDO’s requirements.
This presents a significant advantage, particularly in a conservation area where planning restrictions can often make home improvements challenging. The LDO for Redcliffe Road permits mansard roof extensions within a clear framework, ensuring a balance between homeowners’ needs and the architectural integrity of the area.
Additionally, the LDO provides certainty. Unlike traditional planning applications that can be subjective and dependent on local authority discretion, the LDO establishes fixed guidelines. This helps homeowners plan projects with confidence, with confidence that their project is already acceptable to the RBKC.
What Does the Redcliffe Road LDO Permit?
The Local Development Order for Redcliffe Road establishes a set of precise rules for mansard roof extensions, ensuring they are sympathetic to the historic character of the street while providing homeowners with much-needed additional space.
Adding an extra storey with a mansard roof extension adds a large amount of new family space. Image from our Current Boltons Townhouse projects
Design Parameters
The LDO provides specific design parameters to ensure extensions are in keeping with the character of Redcliffe Road. These focus on the following areas:
1. Demolition Works
Any existing roof elements that do not comply with the LDO guidelines must be removed in preparation for the new mansard extension.
Chimneys, parapets, and cornices must be carefully assessed to ensure their retention or reconstruction in line with conservation requirements.
Redcliffe Road’s Local Development Order requires reinstatement of bottle balustrades
2. Bottle Balustrades & Cornices
Traditional bottle balustrades must be reinstated where necessary to maintain architectural coherence.
Cornices should match existing profiles and be constructed using appropriate materials.
The RBKC Local Development Order diagram of the approved Redcliffe Road mansard extension and associated details
3. Mansards
The mansard roof must adhere to prescribed angles and proportions to maintain harmony with neighbouring properties.
The ridge height must align with adjacent properties to ensure consistency along the terrace.
Dormer windows must be proportionate, timber-framed, and in keeping with the building’s character.
4. Party Walls
Party walls must be extended to match the new roof height.
Any necessary fire safety measures, such as non-combustible materials, must be incorporated into the design.
5. Chimneys
Existing chimneys should be retained where possible, and new ones should match the original design.
If chimneys need to be removed for structural reasons, a suitable heritage-appropriate alternative must be proposed.
6. Solar Panels
Solar panels may be installed but must be carefully positioned to ensure they do not detract from the traditional aesthetic of the mansard roof.
Their placement must align with the slate tiles to maintain a cohesive appearance.
7. Materials
Natural slate must be used for the mansard roof to match existing roofing materials.
Lead flashing and zinc details must be integrated appropriately to ensure durability and aesthetic consistency.
8. Windows & Dormers
Dormer windows should be timber-framed and proportionate to maintain consistency with the original architectural style.
Rooflights, if installed, must be conservation-grade and sit flush with the roof slope.
9. Other Requirements
A Construction Traffic Management Plan (CTMP) and a Site Construction Management Plan (SCMP) must be submitted before work begins. These require specialist consultants to undertake the assessments.
A £5,000 construction bond is required for each property undertaking the works, which ensures compliance with local regulations and minimises disruption to neighbours and infrastructure.
How Much Does a Mansard Loft Conversion Cost?
Mansard extensions involve significant structural work, which makes them more expensive than simpler loft conversions. Additionally, the materials and detailing specified by the Royal Borough of Kensington and Chelsea council are of high quality and are more expensive than standard items, contributing to the overall cost. In London, the cost of a mansard roof extension typically starts at £100,000 and can rise significantly depending on the property’s size, complexity, and level of finish. The average cost per square metre ranges from £2,500 to £4,500 per sqm, depending on specifications, materials, and design requirements.
However, this investment should be considered in the context of property value. Adding a mansard extension to a four-storey house, making it a five-storey home effectively increases the floor area by up to 25%, making it a cost-effective way to enhance your home’s space without moving.
Why work with an architect in Chelsea for a mansard roof Extension?
Although the LDO removes the need for a full planning application, working with an architect ensures your extension is well-designed, fully compliant, and maximises both space and value. Many builders offer a design and build service as an alternative but it is good to bear in mind the following benefits of working with an architect.
1. Expertise in conservation areas
Chelsea’s conservation areas require a sensitive approach to design. An experienced architect will ensure that your extension not only meets the LDO requirements but also complements the street’s historic character, avoiding common pitfalls that could lead to costly modifications.
2. Avoiding costly mistakes
An architect provides detailed construction drawings and specifications, reducing the risk of misinterpretation and expensive errors.
3. Safeguarding construction quality & design integrity
When acting as both architect and contract administrator, we safeguard your design throughout the construction process. Period properties often reveal unforeseen site conditions that differ from expectations. In such cases, we ensure design integrity is maintained, adapting solutions that respect both regulatory requirements and aesthetic principles.
With an architect in place, every detail of the build is monitored to ensure your investment results in a high-quality, durable, and aesthetically coherent extension.
4. Detailed drawings & using the latest technology
Innovative technologies such as 3D visualisation allow you to experience your new space before it’s built. These tools help refine the design and ensure that your vision is fully realised.
Transform your home with a mansard roof extension
If you own a home on Redcliffe Road and are considering a mansard roof extension, now is the perfect time to take advantage of the LDO.
At Nancy Gouldstone Architects, we specialise in designing beautiful and functional mansard roof extensions that respect the unique character of conservation areas. Whether you need early-stage feasibility advice or full architectural and project management services, we can help bring your vision to life.
📩 Get in touch today to discuss your project.
Email: info@nancygouldstone.com
Call: 020 7867 3914