Design guidelines for mansard roof extensions

Thank you to everyone who took part in the public consultation held in September and October 2024. The consultation focussed on proposals to adopt new design guidelines for mansard roof extensions in the Clinton Road, Ropery Street and Tredegar Square Conservation Areas, and to update the existing guidelines for the Driffield Road and Medway Conservation Areas.

The draft guidelines, along with the updated character appraisal and management plans, were considered at a meeting of Cabinet on 18 June 2025. At that meeting, the Mayor decided to adopt the documents, which means they can now be used by residents to help inform planning applications for mansard roof extensions in the relevant conservation areas. The documents will also be used by the council’s planning officers when assessing applications to ensure proposals preserve and enhance the character of the area. A copy of the report, appendices, decision and a link to a webcast of the meeting can be viewed on the Cabinet meeting webpage under item 6.1.

Copies of the adopted documents are available on the right-hand side of this web page. They will also be added to the council’s main website in due course. If you have any general questions about the consultation or the adoption of the guidelines and/or character appraisals and management plans, please contact us at: placeshaping@towerhamlets.gov.uk. If your enquiry relates to a specific property, please use the council’s pre-application advice service or speak to a duty planning officer. General information on applying for planning permission is also available on the council website.

Please note that the Cabinet decision only relates to the new design guidelines for Clinton Road, Ropery Street and Tredegar Square conservation areas, and the updated guidelines for Driffield Road and Medway conservation areas.

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.