The site and background
This case concerned a residential flat in Hackney, where planning permission was sought for a mansard roof extension with an associated roof terrace. The property formed part of a traditional residential terrace within a dense urban area, characterised by a consistent roofline and limited private outdoor space.
The proposal involved the construction of a mansard roof extension to provide additional accommodation, together with a roof terrace at the rear. The design sought to maximise usable internal space while providing external amenity, with the roof terrace positioned to minimise visibility and overlooking.
Planning permission was refused by the council, and an appeal was lodged.
The reason for refusal
The council refused planning permission on the basis that the proposal would harm the character and appearance of the host building and the surrounding area. In particular, concern was raised about the combined visual impact of the mansard roof extension and the roof terrace.
Hackney’s ‘Residential Extensions and Alterations’ guidance document says that altering traditional roofs is unacceptable.
The council also expressed concern that the roof terrace would result in an unacceptable loss of privacy to neighbouring properties through overlooking.
The appeal case
The appeal focused on the detailed design of the proposal and its relationship with the surrounding built form.
In relation to the mansard roof extension, it was explained that the scale, proportions and siting of the extension were consistent with established mansard forms and would sit comfortably within the existing roofscape. The extension was designed to remain subordinate to the host building and to preserve the rhythm and proportions of the terrace.
In respect of the roof terrace, the appeal submissions addressed the council’s privacy concerns directly. It was demonstrated that the terrace would be positioned to the rear, would not be readily visible from the street, and would incorporate appropriate screening to prevent harmful overlooking. The use of obscure glazing and boundary treatments was proposed to ensure that neighbouring residents’ privacy would be protected.
It was further explained that roof terraces are not uncommon in dense urban areas and, where carefully designed, can provide valuable private amenity space without resulting in material planning harm.
The inspector’s decision
The appeal was allowed and planning permission was granted.
The inspector concluded that the mansard roof extension would not appear overly bulky or dominant and would preserve the character and appearance of the host building and the wider area. He found that the design responded appropriately to the existing roof form and the context of the terrace.
In relation to the roof terrace, the inspector was satisfied that the proposed screening and obscure glazing would prevent harmful overlooking and protect neighbouring amenity. He noted that the terrace would be largely concealed from public views and that any residual impact would not be sufficient to justify refusal.
The inspector therefore concluded that the proposal complied with the relevant development plan policies and that the identified concerns did not amount to material planning harm.
Why this case is relevant
Mansard roof extensions combined with roof terraces are frequently refused on the basis of their visual impact and potential overlooking. This case demonstrates that such proposals can succeed on appeal where careful attention is paid to scale, design and privacy mitigation.
It also shows that roof terraces are capable of being acceptable in planning terms, particularly in dense urban areas, provided that their impacts are properly assessed and controlled.
For a wider discussion of how planning appeals for roof terraces are assessed, see our article on planning appeals for balconies and roof terraces.
For another example of a mansard roof extension appeal allowed following refusal, see this case study for a mansard roof extension appeal in Bromley.
Update: support for mansards in the new NPPF
Since this appeal was decided, national planning policy has placed increased emphasis on making effective use of existing buildings, including through well-designed roof extensions such as mansards.
Recent updates to the National Planning Policy Framework encourage local planning authorities to support gentle densification and upward extensions where these can be achieved without harm to character or residential amenity.
While each case must be assessed on its own merits, this policy context reinforces the principle that mansard roof extensions are capable of being acceptable in planning terms when they are carefully designed and appropriately sited.
For a broader discussion of mansard roof extensions and why refusals are often worth challenging on appeal, see our guide to mansard roof extension appeals.
