By Alfie Robinson
What is a mansard? A mansard takes a normal roof, and stretches it upwards to create liveable space. Where a normal roof has little more than trusses, cobwebs, and perhaps some insulation, a mansard tucks away bedrooms, bathrooms and living rooms. The valuable space that’s created can be used in different ways: for new flats, for families to grow, and for intergenerational living.
Prior to December 2023, mansards were built in a piecemeal fashion in the UK. In cities, one sees the occasional structure projecting up from a row of terrace houses, one off, one on. Our discretionary planning system hasn’t had a consistent view on these add-ons. In some cases, upward extensions have been considered ‘permitted development’; in others, not. The caveats to ‘permitted development rights’ are many and complicated. Moreover, huge areas of London—the epicentre of the housing crisis—are covered by conservation areas which remove such rights. In many cases, low-impact extensions have either been refused, or homeowners have simply not bothered.
What’s great about mansards is how much they provide without using additional land space or damaging aesthetics. A mansard piggybacks on an existing house, using an already-developed footprint. The roof extensions are simple in design, and read as a gentle continuation of the roofline. Often, they are barely noticeable at all. The mansard roof has been used for centuries, starting in the 1800s. If their name sounds French, that’s because it is. The feature was used to superb effect in Haussmann’s Paris, augmenting the elegant planned apartments. Beloved by urbanists and tourists alike, the roofline of Paris provides a model for upward expansion without an inkling of change.
Given such a vast proportion of our housing stock consists of terraces built by enterprising 19th century developers, the UK and London particularly are ripe for mansardification. Although these sites can be challenging, when many terraces are of historic interest, the mansard is well-adapted to the design and format of such buildings.
The update to the National Planning Policy Framework in December 2023 acknowledges the virtues of mansards, and now we are beginning to see the benefits. The first planning appeal for a mansard has been won using the updated Framework. (See the appeal here.) The decision allows a new mansard extension, in materials and style matching a 19th century terrace in the Royal Borough of Kensington and Chelsea. As the Planning Inspectorate summarised:
Paragraph 124 of the revised Framework states that planning policies and decisions should allow upward extensions where the development would be consistent with the prevailing height and form of neighbouring properties and the overall street scene. They should also allow mansard roof extensions on suitable properties, where their external appearance harmonises with the original building, including extensions to terraces where one or more of the terraced houses already has a mansard.
Beyond the mansard principle, there are a few important things to note from this appeal decision. Firstly, some older planning policies for local areas which pre-date the 2023 national framework resist to upward extensions. In this recent case at least, the new policy has superseded that resistance:
The proposal would partially conflict with the development plan, in so far as it seeks to resist roof extensions to terraces that are broken by only isolated roof additions. However, the revised Framework is a material consideration to which I afford substantial weight. In this case, I consider that there are material considerations that justify approving the development, despite the partial conflict with the development plan.
Furthermore, there is room for a common sense interpretation of what a ‘mansard’ means. In this case, the definition in policy technically differed from the extension that was proposed, but the Inspectorate went with the spirit of the policy rather than the letter:
Whilst the proposal does not fall within the definition of a mansard roof as set out […] it is a simple variation of this, which is typically found on similar properties across London […] I also acknowledge that the proposal would not create a new home, but as it would result in the enlargement and improvement of an existing home, it would accord with the broad aims of the Framework and its support for upward extensions.
Finally, the Inspectorate emphasised that structural integrity, maintenance and insurance costs are not matters for the planning system. Building regulations are ready to deal with these issues, and they should not deter planning officers and councillors from approving mansards.
Mansards may not be a panacea for the housing crisis, but they can nevertheless be a powerful tool. These extensions will help us get much more use out of the housing stock we already have, while being relatively simple to execute, easy to replicate, and with very little visual impact. The support for such extensions in policy is a welcome move, and individuals and families are already benefiting.
Alfie Robinson is an independent scholar and heritage consultant based in Cornwall. His publications can be found on ResearchGate.
Header image source: Living Tradition by Dr Samuel Hughes. Create Streets (2021). Reproduced with permission.