1–31 Westbourne Terrace, London
1-31 Westbourne Terrace presented an unusual conservation problem. The roots of mature London Plane trees (Platanus x hispanica) had destabilised a long stretch of the Grade II listed terrace's boundary wall, parts of which were leaning or had collapsed beside a busy Westminster highway. Cohanim coordinated a multidisciplinary solution to retain the trees, preserve the character of the listed frontage and make the boundary safe, encompassing planning permission, Listed Building Consent, arboriculture, structural engineering, Building Control information, condition discharge and tender-stage coordination.
What appeared to be a straightforward boundary wall repair proved to be a problem of conservation engineering. The wall forms part of the setting of the Grade II listed terrace, yet the roots of the exceptionally large London Plane trees behind it had displaced its masonry and piers. By 2022 one section had collapsed and further lengths were leaning towards the public footway. The wall, the tree roots and the public highway all competed for the same narrow strip of land. The arboricultural assessment confirmed that the wall could not be rebuilt to its original specification with the trees in place, while Westminster required the character of the wall, piers and black-painted railings to be maintained. The solution therefore adapted the historic boundary geometry locally around the trees, rather than forcing the trees to accommodate a conventional foundation.
The London plane (Platanus x hispanica) is itself the offspring of two travellers. It is generally thought to be a hybrid of the American sycamore (Platanus occidentalis) of North America and the Oriental plane (Platanus orientalis) of south-eastern Europe and western Asia. Exactly where and when the cross occurred is unknown, though it most likely arose in a garden or nursery where both species grew side by side. One account places its first sighting in John Tradescant the Younger's nursery in Lambeth, although firm evidence is scarce. London's oldest surviving plane is believed to be a gnarled specimen in Barnes, in the west of the city.
Restoring part of one of London's great terraces
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.
Full planning permission and Listed Building Consent were submitted in parallel in June 2022. Westminster granted both 22/04069/FULL and 22/04070/LBC on 23 March 2023 for the partial rebuilding of the boundary wall together with new retaining plates and balustrade treatment. The consent accepted the principle of the repair while deliberately reserving the most sensitive details until opening-up and site investigation could establish the precise relationship between roots, masonry and foundations. That was important. It allowed the statutory consent to reflect the reality of working around mature trees rather than pretending that every below-ground condition could be known before work commenced.
The next phase concentrated on Conditions 5, 6 and 8 of the principal planning permission. These required detailed resolution of tree protection (a supervised and auditable arboricultural methodology for work within Root Protection Areas), wall and foundations (final foundation geometry informed by trial excavation, together with local wall, pier and railing modifications), soil retention (structural measures preventing the raised landscaped bed from slipping where sections of conventional masonry could not be reinstated), and the highway interface (accurate coordination between the private boundary and Westminster's adopted highway). Application 24/01538/ADFULL was subsequently approved, with Westminster confirming that the submission fully met Conditions 5, 6 and 8.
London Plane in London Mythology
Coordinating a constrained infrastructure project
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.
Protecting trees through construction, not just on paper
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.
What the project delivered
Chronological summary
| Date | Matter | Achievement |
|---|---|---|
| Early 2022 | Appointment | Cohanim appointed to investigate the deteriorating listed boundary wall and coordinate the repair strategy |
| Mar 2022 | Arboricultural survey | Mature London Plane trees and Root Protection Areas surveyed; direct conflict between major roots and historic wall established |
| 2022 | Structural / architectural development | Bespoke repair strategy developed around retained trees rather than conventional continuous rebuilding |
| Jun 2022 | Planning + LBC | 22/04069/FULL and 22/04070/LBC submitted in parallel |
| 2022 | Multidisciplinary coordination | Structural, arboricultural, architectural, heritage and public-highway requirements brought into a coordinated proposal |
| 23 Mar 2023 | Planning permission | Full planning permission granted for partial rebuilding, retaining plates and balustrade works |
| 23 Mar 2023 | Listed Building Consent | Listed Building Consent granted for the corresponding heritage works |
| 2023 | Technical development | Trial-excavation, root-sensitive foundation, railing and retaining details developed |
| Mar 2024 | Condition discharge | 24/01538/ADFULL submitted addressing Conditions 5, 6 and 8 |
| 2024 | Arboricultural update | BS5837 impact assessment and sequential construction methodology updated following further investigation |
| Dec 2024 | Condition-discharge revisions | Detailed package amended following technical and statutory coordination |
| 2025 | Conditions approved | Westminster confirmed Conditions 5, 6 and 8 were fully met |
| 2022–2025 | Tender / delivery preparation | Building Control and tender information developed alongside stakeholder and consultant coordination |