Design guidelines for mansard roof extensions
The council has adopted design guidelines for mansard roof extensions in five conservation areas. These guidelines give residents more flexibility to extend their homes while ensuring any changes respect the historic character of these areas.
What is a mansard roof?
A mansard roof has two slopes on each side. The lower slope is steeper and the upper one is shallower. This design creates extra living space within the roof while reducing the visual impact on the street by partly hiding the new structure behind the front parapet wall.
Why are guidelines needed?
In many cases the council has discouraged mansard roof extensions in conservation areas because of their impact on historic character. However, some residents have told us they want more flexibility to extend their homes for growing families or changing needs. In response, the council has introduced guidelines for mansard roof extensions in five conservation areas.
Which buildings do the guidelines cover?
The guidelines apply to buildings in these conservation areas:
- Clinton Road
- Driffield Road
- Medway
- Ropery Street
- Tredegar Square
Not all buildings in these areas are suitable for mansard roofs. Some may be better suited to a different type of extension or may not be suitable for any roof extension at all. This includes statutory or locally listed buildings, which have additional heritage sensitivities.
What do the guidelines contain?
The council developed the guidelines with specialist conservation architects. They use clear visuals to show how a mansard roof should be designed so it fits with the original building and minimises harm to the conservation area’s character.
They cover:
- setting the extension back to reduce visual impact
- designing appropriate dormer windows
- treating chimney stacks
- managing rainwater drainage
- achieving suitable stairwell head height
- incorporating solar panels.
The guidelines also explain how the council will manage any harm caused by introducing mansard roofs.
Where can I find the guidelines?
You can view or download the full design guidelines for mansard roof extensions in each conservation area:
How will the council manage harm to the historic environment?
These conservation areas have streets with a consistent architectural style and uniform rooflines that contribute to their character. Mansard roofs can disrupt this harmony, even when designed to the council’s guidelines.
To offset this harm, proposals must include:
- Measures to improve the front of the house, such as repairing or replacing architectural features
- A financial contribution to a streetscape improvement fund, which will pay for public realm improvements that enhance the area’s character and appearance
What if my property is not covered by the guidelines?
Not all properties are suitable for mansard roofs. They are typically terraced houses with a London or V-shaped roof hidden behind a parapet wall. Properties are excluded if they have incompatible roof types, like visible pitched roofs, or if they are too shallow for an extension. The guidance also does not apply to locally or statutory listed buildings.
Other types of roof extension like a rear dormer, might be acceptable. We recommend consulting an architect and using the council’s pre-application advice service to explore options.
What will the streetscape improvement fund be used for?
The fund supports projects that improve the conservation area’s character and appearance. Examples might include:
- tree planting
- better pavements and street lighting
- enhancements to open spaces.
Contributions in Driffield Road and Medway conservation areas have funded new street trees that enhance the streetscape. These trees also provide environmental benefits, including carbon capture, improved air quality and reduced flood risk.
Will the guidelines be extended to other conservation areas?
Currently no budget or resource has been identified to develop guidelines for additional areas. Creating this type of guidance takes time and careful work to balance residents’ aspirations with the council’s duty to protect conservation areas.
We value residents’ interest in shaping the borough’s future. While there are no immediate plans to extend the guidelines, we will continue to monitor community needs as part of our ongoing work.