- Decision
- dismissed, 9 September 2026
- Decided by
- Planning Inspector: K Dryden
- Authority
- Westminster (London)
- Appeal reference
- 6011521
- Application reference
- 25/08827/FULL
- Procedure
- written representations
- Development
- Mansard roof extension to top-floor flat (2-bed to 3-bed)
- Site context
- inside settlement, conservation area
- Green Belt
- No
- Framework applied
- August 2026 NPPF
- Determinative policies
- HE6, S4(1), L2(1)(d)(i), DP3(1)
- Development plan policies
- Westminster City Plan 2019-2040 (2026) Policies 42, 44, 45, Roofs SPD 2004, St John's Wood Conservation Area Audit 2008
- Main issues
- character and appearance; conservation area
Summary
A mansard on a stucco terrace in the St John's Wood Conservation Area, enlarging a top flat from two to three bedrooms, was dismissed. The inspector found low less-than-substantial harm to the CA. The family-home benefit did not outweigh it. L2's airspace support failed its own street-scene/character limb, so the benefits were substantially outweighed under S4. The appellant invoked HO1. The inspector rejected that because HO1 is a plan-making policy.
Issues and findings
- Transition. The parties commented on the August 2026 Framework (DL ¶3).
- Heritage, HE6/HE9: HARM (low). "the introduction of mansard cheeks, increased roof height, and the raising of the parapet walls and associated chimney stacks would appear discordant ... prominent and incongruous" (DL ¶10). "even a low level of harm to the significance of a designated heritage asset carries considerable importance and weight" (DL ¶17). The benefits were "comfortably outweighed" (DL ¶18). The appellant had also not shown the benefits could not be achieved in a less harmful way (DL ¶19).
- L2 airspace: FAIL. "the Framework Policy L2 1.d)i. requires such development to be consistent with the overall street scene, or that building upwards would not cause substantial harm to the character of a building and its surroundings" (DL ¶26).
- Glossary definition is not permission. "whilst the appellant has set out that the proposal meets the definition of a 'mansard roof extension' within the glossary of the Framework, this does not imply that the proposed development is acceptable" (DL ¶27).
- HO1 not a decision-making policy. "the appellant draws my attention to Policy HO1 of the Framework, where this policy relates to plan-making and not decision making policies" (DL ¶28).
Planning balance
This was the S4 balance (DL ¶25). The benefits were HO7 family accommodation and efficient use of the building. Against them were HE6 harm and conflict with L2(1)(d)(i) and DP3(1). "Taken together, I find the benefits of the proposal would be substantially outweighed by the adverse effects ... Policy S4 of the Framework does not point to permission being granted" (DL ¶29).
What made the difference
The unaltered roofscape on this part of the terrace, and the CA audit singling it out as unsuitable for roof extensions. Mansards at the far end of the terrace predated the current plan. The heritage balance (HE6) decided the S4 balance.
Transferable points
- The new Framework's mansard definition and L2 airspace support do not override heritage harm. L2(1)(d)(i) has its own character test (DL ¶26-27).
- HO1 is a plan-making policy and gives no decision-making support (DL ¶28). This contrasts with PINS-6010946, which used HO1 as a source of harm.
- Low less-than-substantial harm still carries "considerable importance and weight" and can outweigh a family-home benefit (DL ¶17-19).
- Older neighbouring roof extensions granted under previous plans are not comparable (DL ¶13).
Policy findings
Policy codes are those of the National Planning Policy Framework (August 2026) unless a development plan is named.
| Policy | Finding | Weight | Note |
|---|---|---|---|
| HE6 | harm | considerable | low harm to St John's Wood CA from mansard on largely unaltered butterfly-roof terrace; benefits "comfortably outweighed" (DL 16-19) |
| L2(1)(d)(i) | fail | substantial weight to upward extension depends on consistency with street scene or no substantial harm to building's character; not met (DL 26) | |
| S4(1) | fail | benefits substantially outweighed; S4 "does not point to permission being granted" (DL 29) | |
| HO1 | not-engaged | appellant's reliance rejected - HO1 "relates to plan-making and not decision making policies" (DL 28) | |
| HO7 | benefit | larger family-sized unit; does not outweigh heritage harm (DL 28) |
Key facts
- Terrace identified in the CA audit (Fig 56) where roof extensions would not normally be acceptable; older mansards at the east end not comparable (DL 13)
- Meeting the Framework glossary definition of "mansard roof extension" does not imply acceptability (DL 27)
- Amended plans submitted at appeal were not accepted (Wheatcroft/procedure guide) (DL 5)
Related decisions
Sources
This note is one of the decisions behind the NPPF 2026 Navigator, which shows how each Framework test has been applied across all the decisions in the database. Also available as Markdown.