The proposed roof extension with railings, due to its height, bulk, design and location on a terrace which only has isolated additions, would be harmful to the roofline of this side of the street and visually intrusive in views within the conservation area and therefore would fail to preserve or enhance the character and appearance of the Chelsea Conservation Area. As such, the development would be contrary to policies of the development plan, in particular policies CL1, CL3, CL8 and CL11 of the Local Plan 2019.