Design guidelines for mansard roof extensions

The council is proposing to adopt mansard roof design guidelines for three conservation areas, Clinton Road, Ropery Street and Tredegar Square. The council also plans to update existing guidelines for Driffield Road and Medway conservation areas. If approved, the guidelines will help residents to get planning permission to extend their homes upwards with a mansard roof. Alongside the new and updated guidelines, the council is also proposing to update the character appraisals and management plans for these five conservation areas.

A public consultation on these proposals was held between 13 September and 27 October 2024 and we are carefully considering all the responses that were received.

The decision on whether to adopt the guidelines will be made by the Mayor at a meeting of Cabinet. In preparation for this, the proposed guidelines need to go through an internal scrutiny process. Meetings of the Cabinet are normally held monthly on a Wednesday evening at the Town Hall and are open to the public to attend. At present we anticipate the meeting to take place in the spring of this year. The date of the meeting will be published here in advance, notification emails will also be sent to anyone who responded to the consultation.

What is a mansard roof?

A mansard is a type of roof that features two slopes on each side, the lower slope is steeper, and the upper one is shallower. They are used to provide an extra living space within the roof, while limiting the impact on the streetscape by partially hiding the new roof structure behind the front parapet wall.

Why are the guidelines needed?

In the past, the council has discouraged adding mansard roof extensions to many properties in conservation areas due to concerns about the impact they have on the historic environment. However, in 2017 the council adopted mansard roof guidelines for Driffield Road and Medway conservation areas. This was because many residents told us that they would like greater flexibility to extend their homes to accommodate growing families or adapt to changing circumstances.

Since then, we have heard from residents in other areas, who would welcome a similar approach. As a result, the council is now considering extending the approach to three more conservation areas. At the same time, the council is proposing to update the existing guidelines for Driffield Road and Medway conservation areas, the design principles will remain the same, but they will be made clearer and easier to use, with some additional information.

Which buildings will the guidance cover?

The council has prepared new draft guidance for Clinton Road, Tredegar Square and Ropery Street conservation areas, and updated guidance for Driffield Road and Medway conservation areas.

The guidance shows exactly which properties in these areas it applies to. Not all buildings in the conservation areas are suitable for mansard roof extensions. This may be because a different type of roof extension is more appropriate. Some buildings may not be suitable for any kind of roof extension at all, this may include buildings that are statutory or locally listed, which have additional heritage sensitivities.

What does the guidance contain?

The guidelines have been developed by the council in conjunction with specialist conservation architects. They explain in clear visual terms how a mansard roof extension should be designed to ensure that it harmonises with the original building and minimises harm to the character and appearance of the conservation area. It covers things like how to:

• set the extension back to reduce visual intrusion
• design appropriate dormer windows
• treat chimney stacks
• design rainwater drainage
• best achieve a suitable stairwell head height
• incorporate solar panels.

The guidelines also set out how the council will manage harm to the character and appearance of the conservation areas that arises from the introduction of mansard roof extensions.

How will the council manage harm to the historic environment?

The residential streets of these conservation areas typically have a consistent architectural form with a strong uniform roofline that makes a positive contribution to the character of the area. The introduction of mansard roofs can disrupt and cause harm to this, even where they are designed in accordance with the council's guidance. To help mitigate this harm, the council proposes that roof extensions are accompanied by enhancement works to the front of the host building, that will improve the character and appearance of the area. The council also suggests that proposals for mansard roofs are accompanied by a commitment to make a financial contribution to a streetscape improvement fund. This will be used to deliver public realm improvements that will help to further offset the harm from mansard roof extensions.

What if I have questions about the guidelines?

Please see the frequently asked questions section of this page. If you require any other information, please contact us at placeshaping@towerhamlets.gov.uk.