The building stock problem

The majority of commercial office space in London was built before Cat6A existed. Victorian terraces in the City, post-war office blocks in Holborn, 1980s towers in Canary Wharf, converted warehouses in Bermondsey, much of London’s commercial building stock runs on cabling infrastructure that was installed between 1995 and 2010. Cat5e or early Cat6, installed to a bare pass, routed through conduit and cable trays that were never designed for the density of connections a modern AI-ready office requires.

Upgrading these buildings for AI network infrastructure is not straightforward, but it is done every week by contractors who understand both the technology requirement and the physical constraints of occupied, historic and listed buildings. ACCL has been doing this work across London for 28 years. This is the practical guide to how it is approached.

Start with an audit first

The single most common mistake in legacy building upgrades is skipping the audit. An IT Director or Facilities Manager sees a Cat5e installation, assumes it all needs replacing, and signs off a full rip-and-replace budget. The audit frequently reveals that a significant proportion of existing cable runs are serviceable, they may not pass at Cat6A specification, but they pass comfortably at Cat6 and can support current applications reliably for another five to ten years.

ACCL’s physical layer audits using Fluke DSX CableAnalyser test every existing link against current standards. The output is a clear, ranked list: links that are performing well and should be retained, links that are marginal and should be prioritised for replacement, and links that are failing and need immediate attention. That data turns a gut-feel upgrade decision into an evidence-based phased programme, which is the only way to manage a legacy building upgrade without disrupting the occupants.

The single most common mistake in legacy building upgrades is skipping the audit.

Victorian and Edwardian buildings: the specific challenges

Solid masonry walls, corniced ceilings, cast-iron structural elements and listed building consent requirements make Victorian and Edwardian offices some of the most technically challenging cable installation environments in London. The challenges are real, but they are manageable with the right approach.

• Cable routing: Surface-mounted trunking in heritage buildings is often the only option where chasing into walls requires listed building consent. Correctly specified and neatly installed trunking in period buildings is visually acceptable and often preferred by planning officers to concealed but poorly finished work.
• Comms room location: Victorian buildings often lack dedicated comms rooms. Converting a store cupboard, stairwell landing or understairs space into a compliant comms room, with adequate ventilation, access control and power, is a standard part of a legacy upgrade project.
• Density constraints: Existing conduit was sized for the cable density of 20 years ago. In many cases, existing conduit must be supplemented with new surface trunking rather than attempting to pull modern, larger-diameter Cat6A cable through conduit that was never sized for it.
• Coordination with tenants: In multi-tenanted Victorian office buildings, cable routes often pass through areas occupied by other tenants. Early engagement with building management and neighbouring tenants to plan access is essential and is frequently overlooked until it causes programme delays.

Converted warehouses and industrial buildings

Converted warehouse buildings, common across Bermondsey, Hackney, Shoreditch and the wider East London area, present a different set of constraints. Open floor plates, exposed structural elements and high ceilings make routing decisions relatively straightforward. But the existing cabling in these buildings is often the most chaotic: a patchwork of installations by multiple tenants over multiple years, with no documentation, no consistent labelling and no coherent topology.

In warehouse conversions, the audit almost always reveals a cabling installation that cannot be upgraded, it has to be replaced in full. The positive side of this is that the open floor plate and exposed structure makes full replacement significantly faster and less disruptive than in a traditional office building. Cable trays can be installed at height and cable runs routed cleanly without the access constraints of a traditional fit-out.

The phased upgrade model for occupied buildings

For any occupied building, the upgrade must be planned around the occupants’ working patterns. ACCL uses a standard phased model that has been refined over 28 years of working in occupied London offices:

• Phase 1: Audit and documentation. No physical work, no disruption. Fluke DSX testing and as-found drawing production. Typically completed over a single weekend.
• Phase 2: Comms room upgrade. New patch panels, cable management, switch hardware and power distribution. Usually completed over a single weekend shutdown of 48 hours.
• Phase 3: Priority link replacement. The worst-performing existing links replaced with Cat6A, one floor at a time, working outside business hours. Each floor is completed and tested before the next begins.
• Phase 4: Full Cat6A installation to new locations. New data points for AI devices, access points, CCTV cameras and IoT sensors. Completed floor by floor, outside business hours.
• Phase 5: Final certification. Full Fluke DSX test report for all links, as-built drawings, TIA-606-B labelling audit, and handover documentation.