A complex structural intervention at a central London conversion project has enabled redevelopment above occupied shops. Regiis managing director Ryan Newberry explains how using Pynford beams to transfer loads through the existing masonry core provided the answer.
At 126-134 Baker Street in Marylebone, chartered building company Regiis is transforming a central London building into 16 apartments, with a rear extension and additional accommodation at roof level.
The project combines facade retention, extensive internal demolition, new floor structures and major structural alterations. Its defining challenge was to strengthen the building above a parade of occupied shops, where access to inspect or improve the foundations was not available.
The existing structure and the constraints of the occupied commercial units meant that conventional underpinning or large-scale temporary propping inside the shops was not practical.
The design team needed to develop a solution that could establish a reliable load path through the existing masonry core, without relying on intrusive access to the foundations. Regiis helped coordinate the design review and construction sequence to turn that challenge into a buildable structural solution.
Pynford beam arrangement
Working with the structural engineer and wider design team, Regiis developed a Pynford beam arrangement within the core walls, above the shop line. Pynford beams are reinforced concrete beams formed in sections within existing masonry. Short lengths of wall are carefully opened and locally supported on temporary steel stools.
Reinforcement and any required sleeves are installed before the concrete is placed. Once it reaches the specified strength, the completed beam provides continuous support within the wall.
At Baker Street, the beam levels and connections had to be coordinated with the available wall and floor geometry. The team reviewed reinforcement, enlarged plates, holding-down arrangements, drainage and service penetrations before the concrete was poured.
Fixing these interfaces early was essential: later cutting into the beams could compromise their structural function. Temporary propping and chimney stabilisation were also put in place before adjacent masonry and floors were disturbed.
The beams formed one part of a carefully controlled sequence. The retained facade, masonry core, existing floors, temporary works and new frame had to remain stable as a connected system. A waler system distributed restraint across the facade, while internal temporary works supported critical elements.
Demolition proceeded in defined zones, with each section released only when its replacement support was secure. The original floors are being replaced with new structures, including steelwork and rib deck slabs, set at revised levels for the residential layout.
Limited space
Logistics added another layer of complexity. The site sits on a Red Route, with limited space for deliveries, lifting and waste removal. Regiis coordinated the construction sequence with the scaffold arrangement and integrated a spider crane to move materials within the site envelope, reducing reliance on road occupation.
Work above occupied businesses also demanded close control of noise, vibration, temporary support and access to the commercial units.
Following the Pynford beam installation, extensive waterproofing was applied to the associated slab and interfaces, with particular attention to penetrations, junctions and changes in level. The beam pairs were cast in April 2026, following coordination of the temporary works, reinforcement, connections and service routes.
The project demonstrates how a carefully designed structural intervention can help unlock commercial-to-residential conversion in constrained urban locations.
Where foundation access is restricted, a Pynford beam solution within a suitable masonry core may provide an alternative route for transferring loads—provided the existing structure, temporary works, sequencing and interfaces are rigorously assessed.
At Baker Street, that approach is enabling major redevelopment above occupied shops while protecting the businesses below and creating a new residential use for a tightly constrained central London building.
