Constructing data centres: legal considerations in a rapidly scaling UK market (part 2 - managing design considerations, interfaces and modularisation)

Design coordination: allocating responsibility early and clearly

Data centre design is characterised by dense MEP integration, tight plant tolerances and continual revision in response to changing technology standards. This makes clear allocation of design responsibility essential.

A recurring theme we observe across UK projects is uncertainty over the boundary between employer retained design, consultant design and contractor design. This can manifest in NEC4 ECC under ambiguously drafted Scope documents or in D&B projects where Employer’s Requirements do not fully articulate what constitutes “design intent” versus “performance criteria”. These ambiguities can lead to disputes over whether issues stem from the contractor’s design or the employer’s prescribed solution.

To mitigate this risk, contracts should be clear in relation to any acceptance of full design responsibility by the contractor, embed structured design review cycles, clear information‑release schedules, and explicit obligations around BIM coordination. For hyperscaler-led projects, where occupiers frequently retain control of certain standards or issue late-stage revisions, it is equally important that the contract is clear how such changes will be assessed in relation to programme impact and compensation.

Interface risk: the hidden driver of delay and claims

Interface issues can be a cause of delay in UK data centre projects. Multiple tiers of subcontractors, vendor-supplied specialist equipment, and overlapping civil, structural and MEP packages mean that poorly defined interface obligations quickly create gaps in accountability. The employer may be protected by the main contractor taking single point responsibility but this interface is then something that requires to be managed by the main contractor.

Equipment like generators, UPS systems[1], switchgear and integrated cooling units often sit outside the contractor’s usual procurement chain. In turnkey contracts these items will require to be procured by the contractor who will be responsible for relevant interfaces but in some circumstances they may be procured by the employer “free issue” to the contractor although the contractor may still be required to “wrap” such items be responsible for the same. Either way one will need to consider relevant interface schedules, responsibilities for setting-out, tolerances, handling, installation, testing attendance and warranty alignment in both the main contract and the subcontracts in order that the risk of misalignment does not fall into a grey zone.

Similarly, where shell‑and‑core works and fit-out packages are let separately, the shell contractor must be given clear obligations regarding loadings, penetrations, spatial allowances and temporary works needed for later trades. Incomplete or vague Employer’s Requirements in these areas may result in claims for compensation events or variations once the fit‑out contractor mobilises.

Interface risk also extends to utilities. Even though broader grid constraints fall outside the scope of this blog series, the contractual relationship between utility providers/ICPs[2] and the main works contractor must still be clearly managed, particularly where energisation dates drive commissioning milestones.

Modularisation and offsite fabrication: unlocking efficiency, creating new risks 

The data centre sector is increasingly turning to modular and offsite solutions to deal with programme compression and labour‑market constraints. Modular MEP skids[1], containerised UPS systems and prefabricated plant rooms are now common features on several UK sites[2].

However, these bring new legal considerations. Title and risk transfer become more complex when large elements of the works are constructed away from site. Contracts should address who bears the risk of damage during factory testing, transport and pre-installation storage. Payment milestones linked to offsite works require careful integration with testing obligations such as Factory Acceptance Tests and Site Acceptance Tests. Modularisation also magnifies the need for early design freeze. Where modules are built on accelerated manufacturing schedules, late design amendments, even minor dimensional changes, can result in significant rework costs. Ensuring that contractor proposals clearly demonstrate mechanical and digital integration with wider systems (including BMS, EMS and control infrastructure) is essential to avoid disputes during commissioning.

Conclusion

As the UK data centre market accelerates and developers increasingly seek repeatable, scalable delivery models, the contractual treatment of design coordination, interfaces and modularisation is emerging as a key differentiator between projects that succeed and those that face delay, cost escalation and performance issues. Getting these fundamentals right at the outset is essential.

In part three, we will examine the later-stage issues that determine whether a facility performs as intended, covering testing and commissioning strategies, security considerations and the growing influence of sustainability obligations on contractual risk allocation.