IN Brief:
- Perega has been appointed by Severfield to design secondary roof steelwork for Old Oak Common station.
- The design must avoid penetrations through the primary steel while accommodating blast loading and irregular geometry.
- Detailed connection modelling will support a roof programme due to move further into installation during 2027.
Perega has secured its first HS2 appointment, taking responsibility for secondary steelwork design supporting the roof at Old Oak Common station in west London.
Main steelwork contractor Severfield has appointed the structural engineering consultancy to design purlins, roof and soffit support elements, edge details, roof walkways, and brackets for guttering and rainwater chutes. Perega’s role is design-only, with Severfield retaining responsibility for the steelwork model.
The package sits within a roof structure where apparently minor secondary elements have to work around unusually restrictive interfaces. No penetrations are permitted through the primary steel, so fixings must connect to welded tabs and connection points already provided on the main members rather than passing through the structure.
Blast-loading requirements add another design condition. Perega says connections are being detailed so that the structural member fails before the connection, increasing the importance of connection capacity, load paths, and coordination without simply adding unnecessary steel.
Geometry is another constraint. Old Oak Common’s T-shaped form means areas that appear similar in plan can require different detailing, particularly around end bays, transitions, soffit supports, and roof edges. Repetition is therefore limited compared with a more regular secondary-steel package.
Perega has used 3D modelling and IDEA StatiCa more extensively than on its previous secondary-steelwork projects to manage the connection design. Brackets have also been redesigned to remove enclosed box sections where possible, reducing steel content while simplifying detailing and future maintenance.
Adam Holliday, senior structural engineer at Perega, said: “The end bays have their own unique details; you can’t simply repeat what you’ve already designed in the central section.”
The design work comes as Old Oak Common progresses through major structural and fit-out stages. HS2 confirmed in August that all six underground high-speed platforms had been constructed inside the station box, using 1,946 precast slabs installed over in-situ invert walls.
Each slab measures up to 2m by 4m and weighs between four and five tonnes. The void beneath the platforms will carry services, while further work will add staff and equipment rooms, lift and escalator steelwork, and floor finishes.
Eight conventional platforms are also planned at ground level for the Elizabeth line, Great Western Main Line, and Heathrow Express. Together with the six high-speed platforms, they will make Old Oak Common a 14-platform interchange linking HS2 with existing rail networks in west London.
HS2 says installation of the main station roof is due to begin in 2027. That timetable puts increasing weight on the coordination of specialist structural packages because secondary supports, walkways, drainage, soffits, and architectural interfaces have to be resolved before enclosure work advances.
The restriction on penetrating the primary steel narrows the room for late changes. A support moved after fabrication cannot simply be fixed wherever convenient if the main frame has only defined welded connection points, so dimensional control and model coordination become part of the construction risk rather than an isolated design exercise.
The drainage and maintenance elements also have to remain accessible after completion. Gutter brackets, rainwater-chute supports, and roof walkways may carry smaller loads than the primary frame, but their detailing affects inspection, replacement, water management, and safe access over the life of the station.
Reducing enclosed box sections can help on both fabrication and maintenance. Fewer closed details mean less steel and fewer concealed surfaces, although each revised bracket still has to satisfy the same structural, geometric, and blast requirements.
Secondary steelwork also sits at the boundary between several specialist trades. Roof coverings, soffit systems, drainage, access arrangements, and structural steel may be designed by different teams, but their fixing points and tolerances have to agree in the same model before fabrication. At Old Oak Common, the ban on primary-steel penetrations makes those interfaces less forgiving because an uncoordinated late change cannot be solved simply by drilling another connection into the main frame.
Old Oak Common is already one of the largest active station projects in the UK, and its scale can obscure the significance of smaller design packages. The roof will ultimately depend on hundreds of interfaces behaving as intended, with secondary steel connecting architectural systems and maintenance infrastructure back to the main frame.
Perega’s appointment places it in that interface-heavy part of the programme. The consultancy is not designing the primary station structure, but the success of its package will be judged by whether the roof’s secondary elements can be fabricated, installed, inspected, and maintained without forcing changes into steelwork already fixed around strict connection rules.
