1–31 Westbourne Terrace, London

Nos. 1–31 Westbourne Terrace form a Grade II listed mid-19th-century terrace within the Bayswater Conservation Area. The terrace was constructed during the development of Tyburnia and forms part of the distinctive sequence of stucco-fronted buildings running along Westbourne Terrace. The boundary treatment is visually subordinate to the main building, but because of its length and repetition it makes an important contribution to the public realm. The full highway-facing boundary extends for approximately 115 metres, with around 85 metres associated with the client's ownership. The project therefore concerned considerably more than repairing individual cracks: it affected the visual base of an extensive listed frontage.

The design developed through close coordination between architecture, structural engineering and arboriculture. Rather than proposing one standard wall section everywhere, the solution responded individually to the conditions around each major tree, including locally altering wall and pier geometry, creating gaps and reduced-width profiles where required by tree trunks and roots, adapting railing arrangements around retained trees, developing foundation positions from trial excavation rather than assumptions, introducing structural retaining elements where masonry could no longer safely retain the raised soil, and establishing controlled excavation methodologies within Root Protection Areas. Westminster ultimately required precisely this site-specific approach as part of the consent.

The simplest heritage response would have been to reproduce the historic wall exactly. At Westbourne Terrace, that would also have been the wrong response. The trees had physically occupied part of the space in which the original construction once stood. Attempting to force conventional masonry foundations back through established root systems would have endangered trees that themselves contribute materially to the character of the Conservation Area. The project therefore demonstrates an important conservation principle: preserving character does not always require preserving every historic dimension unchanged. The design maintains the rhythm, materials, colour and architectural language of the boundary while allowing local deviations where necessary for the long-term survival of the trees. The historic streetscape is consequently protected as a whole rather than at the expense of one of the elements which makes that streetscape distinctive.

Cohanim's role continued into detailed design and tender preparation. The commission required coordination between architecture, structural engineering, arboriculture, heritage and planning, Building Control, highway requirements, contractor methodology, and the management requirements of an occupied residential property. Technical and tender information was prepared while managing a stakeholder environment involving more than 30 residential and commercial leaseholders together with the managing agent, Westminster officers and specialist consultants. For what appears externally to be a relatively simple boundary wall, the statutory and technical coordination was consequently comparable with a much larger building project.

The arboricultural work continued well beyond the planning submission. The BS5837 assessment was updated during the technical development of the project and ultimately incorporated a sequential Arboricultural Method Statement addressing supervision, tree management, protection measures, access, demolition, excavation, foundations, drainage and future tree work. This was particularly important because large roots were observed running immediately against and beneath the wall. The methodology therefore anticipated that some construction details would need to be adjusted in response to what was actually discovered during careful excavation.