The construction industry is quietly undergoing one of its most significant shifts in decades. As projects become more complex, more constrained, and more dependent on specialist expertise, the traditional “single‑stage” design and build model is starting to show its limits. Developers want earlier starts. Designers want more time. Contractors want clearer risk boundaries. And everyone wants fewer surprises.

This is where phased design & build is stepping forward — not as a workaround, but as a smarter, more strategic way to deliver complex structural works.

At Cambell Brown Engineers, we’ve been at the centre of this shift. We’ve seen first‑hand how phased procurement can unlock programme, reduce risk, and give clients the flexibility they need without compromising design integrity. But we’ve also seen how easily it can go wrong when the industry treats it as a simple contract split rather than a fundamentally different delivery model.

It’s time to rethink how we approach early structural packages — and what “good” looks like.

The Rise of the Specialist‑Led Structural Phase

A decade ago, enabling works were modest: demolition, site establishment, utilities. Today, they often include full basements, complex temporary works, piled walls, waterproofing, and even major portions of the superstructure.

This evolution reflects a simple truth:

Specialist structural contractors now have the capability — and the appetite — to deliver major structural packages under design & build.

But capability alone isn’t enough. The industry must recognise that structural contractors excel at structural design, temporary works, and delivery — not at coordinating facades, MEP, lifts, BMUs, or architectural interfaces that may not yet exist at tender stage.

The Real Challenge: Design Responsibility in a Moving Environment

Some structural elements are clean, self‑contained, and ideal for early procurement — demolition, utilities, foundations, piles, drainage, and below‑ground waterproofing. These can be designed and delivered by a structural contractor with minimal risk.

But what about rafts, cores, or even parts of the superstructure? Yes, a structural contractor has the technical competence to design them. The real question is: should they?

  • Will the lift fit the shaft when no lift design exists?
  • Will the riser be large enough when the M&E strategy is still a sketch?
  • Will the structure meet the needs of the next phase when that phase hasn’t been designed?

A structural contractor can deliver a structure — but without whole‑building information, they cannot guarantee it will be the right structure.

And before we assume we can simply “write this into the contract,” we need to ask whether that truly sets the project up for success. Are we empowering the structural contractor, or asking them to take responsibility for design decisions that will only be made months later by others? Cores, rafts, and superstructures with façade or services interfaces require whole‑building knowledge. This is the domain of the main contractor and the full design team. Their performance criteria depend on information that simply doesn’t exist at the point of structural tender. Here’s the uncomfortable truth the industry often avoids:

You cannot outsource design responsibility for elements that depend on future design decisions.

A phased contract only works when design demarcation is deliberate, not convenient. At Cambell Brown Engineers, we recommend that coordination risk remains with the client and their design team, while the structural contractor undertakes a clearly defined contractor‑designed portion. Then all designers and the structural Contractor are novated to the main contractor.

Two Contracts, Two Designs, Two Digital Worlds

One of the most overlooked aspects of phased procurement is digital separation. A phased contract is not one project delivered in two parts — it is two projects, each with its own

  • Contract
  • CDE
  • BIM model
  • Drawing set
  • Approval pathway

Trying to run both phases through a single model or drawing set is a guaranteed route to confusion. The employer’s engineer is designing a building. The contractor’s engineer is delivering a building. These are different tasks with different outputs.

At CBE, we advocate for — and implement — a clean digital split. It protects all parties, reduces rework, and ensures that each contract is administered on its own terms.

Dual Roles for Engineers: A Modern Necessity

One of the most misunderstood — yet most powerful — aspects of phased procurement is the role of the structural engineer. In the right setup, the engineer can — and often should — support both the employer and the structural contractor, but only when the two roles are kept entirely separate.

That separation isn’t duplication. It’s governance.
The employer’s engineer is responsible for the coordination.
The contractor’s engineer is responsible for the delivery.

These are fundamentally different tasks, requiring independent models, independent drawing sets, and independent responsibilities.

This clear divide protects design intent, avoids conflicting priorities, and prevents engineers being pulled into informal coordination roles outside their appointment. And where the design is still evolving, dual roles may introduce a conflict of interest — in those cases, it can be advantageous for the contractor to appoint their own structural engineer.

CBE regularly supports this approach. Whether we act for the employer, the contractor, or both under separate appointments, we maintain clean boundaries, transparent communication, and a coordinated design history that the main contractor can confidently inherit at novation.

Why Phased Procurement Is Becoming a Strategic Advantage

When structured correctly, phased design & build offers clients something incredibly valuable:

  • Early start without premature design freeze
  • Reduced risk from existing conditions
  • Specialist-led structural delivery
  • Maintained design flexibility for the main works
  • Clearer allocation of design responsibility

But the real advantage is cultural. Phased procurement forces the industry to be more intentional about design boundaries, digital workflows, and contractual clarity. It rewards teams who plan ahead, coordinate early, and understand the difference between structural design and whole‑building design.

At Cambell Brown Engineers, we believe phased procurement isn’t just a trend — it’s a sign of a maturing industry. One that recognises that complexity demands structure, clarity, and specialist leadership.

The Future: Phased Delivery as Standard Practice

As buildings become more complex and programmes become more compressed, phased design & build will continue to grow. But its success depends on the industry adopting a more disciplined, structured approach — one that respects the boundaries between phases, responsibilities, and design intent.

Our view is simple:

Phased procurement works brilliantly when it is treated as two independent projects that must fit together — not one project artificially split in two.

This is the mindset shift that will define the next generation of complex urban development.