34 Portland Place & 73 New Cavendish Street, London

At 34 Portland Place, a major objective is to recover the legibility and hierarchy of the original townhouse. The proposals include the reinstatement of principal rooms, removal of unsympathetic later subdivisions, recovery of historic openings and improvement of the relationship between principal and subsidiary spaces. A Georgian enfilade is being restored, individual principal rooms are being returned to their original proportions and lost architectural details are being reconsidered using documentary evidence. The project also proposes a historically appropriate fireplace where one had been entirely removed and the reinstatement of an Adam-style ceiling for which archival evidence survives. The objective is not stylistic reproduction for its own sake. It is to restore architectural hierarchy where evidence makes that restoration defensible.

Fire engineering is one of the project's most technically significant workstreams. Although the primary project comprises 34 Portland Place and 73 New Cavendish Street, the historic means-of-escape arrangements connect the scheme directly with 36 Portland Place, so life-safety strategy, neighbouring interests and implementation sequencing extend across three buildings. The proposal to remove the existing reciprocal escape arrangement and reinstate the original separation between 34 and 36 Portland Place has required disciplined coordination across the project's own fire engineers and Building Control adviser, the Freeholder, neighbouring occupiers and separately appointed fire advisers acting for the adjoining property - each with distinct legal, regulatory and commercial interests to be reconciled within a single, controlled programme. Running alongside multiple planning and Listed Building Consent applications, this has called for a firm command of the statutory and leasehold position as much as the technical one. Conventional compliance solutions can themselves cause significant harm in historic buildings. Working closely with the fire engineering team, we developed a water-mist suppression strategy as an alternative to conventional sprinklers, supported by enhanced compartmentation, protected escape routes and performance-based justification, limiting the need for extensive new pipework through important ceilings and decorative fabric. Building Control has indicated in-principle acceptance of the water-mist approach, and the position has since been verified through independent specialist review of the strategy and its regulatory basis.

The Howard de Walden Estate is one of the most important great estates in London and in this case the Freeholder of the site and many of the adjoining neighbours, so a separate Licence to Alter process sits alongside the Westminster planning and Listed Building Consent process. Cohanim has been coordinating information - architectural drawings, fire and means-of-escape information, technical proposals and matters affecting adjoining properties - so that statutory and Freeholder reviews can progress in parallel rather than sequentially. Freeholder review, board approval requirements and fire-safety review remain active project dependencies. Further to this, our team makes a point of building a sustainable and friendly relationship with the stakeholders, which is what has successfully transpired.

Given the age of the buildings, many substances and interventions can include hazardous materials, such as lead paint and asbestos, among others. To carry out the work effectively, with design solutions that are acceptable from a heritage perspective, scientific and health and safety investigations began during the earliest project stages. The specialist consultant register includes Mark Womersley and Eton Group for management survey work and damp / mycological investigation, along with several laboratories, and the project archive contains dedicated management-survey, mould-survey and asbestos-remediation documentation. This work has allowed hazardous materials, moisture, mould and existing-condition risks to be considered as part of the design rather than being left as contractor-stage surprises. The early action records also show investigation of historical asbestos records, confirmation of previous remediation, consultation with hazardous-material specialists and separate damp / mycological appointments from the opening weeks of the project. In conjunction with Alan Baxter, specialist timber surveys were also conducted to assist with those investigations and subsequent proposal specifications.

Existing listed buildings rarely conform neatly to modern drawings, so structural design has developed alongside surveys, opening-up and continuing site verification. The Stage 4 work includes new and altered openings, local strengthening, riser interfaces, roof structures, lift shafts and pits, existing steelwork, basement interventions and the relationship of new services with historic structure. Many of these elements simultaneously engage heritage and Party Wall considerations. The project is consequently being designed iteratively: survey, model, inspect, coordinate, verify and then detail.

The existing services had reached or passed the end of their practical operational life. A complete services strategy has therefore been developed across mechanical, electrical, public health, lighting, fire alarm, security, suppression, gas, water and associated systems. By Q3 2026, the architectural review register included coordinated packages for lighting and fire alarm, mechanical services, public health and water, schematics, small power, gas, security and sprinkler services. Rather than simply lowering whole ceilings to accommodate ductwork, the design team has repeatedly reviewed service routes, perimeter zones, localised bulkheads and plant positions to protect ceiling heights in the principal spaces - an approach documented in the Q1 2026 progress record across reception, office and multifunctional rooms, including localised service zones designed specifically to avoid unnecessary reductions in ceiling height. The objective throughout is to use later voids, less significant fabric and existing service zones wherever possible so that improved performance does not come at the expense of the historic interiors.

Inclusive access is another major part of the project. The wider strategy includes accessible WC provision, improved entrance arrangements and new lift infrastructure. At 73 New Cavendish Street, a new passenger lift is proposed within later fabric to provide substantially improved step-free circulation while reducing the impact upon significant historic material. Lift works have required their own coordination across structure, Party Wall considerations, Building Control, fire strategy and specialist lift design.

The project is unusual in having to accommodate formal diplomatic representation, private residential life, working offices and public-facing cultural activity within the same connected estate. That affects almost every discipline. Security, fire strategy and circulation must distinguish public, staff, guest and private areas. The representative spaces at 34 Portland Place must retain the architectural formality of the historic house while functioning for contemporary diplomatic events, while the Cultural Institute at 73 New Cavendish Street must accommodate public engagement, exhibitions and multifunctional uses while sharing infrastructure with secure diplomatic functions. The design therefore needs to work at both ceremonial and everyday scales.