Design-Build for Multiplex Projects
Why Separating Designer and Contractor Increases Risk in Multiplex Projects
Multiplex development often appears straightforward, essentially a small multi unit residential building. In practice, multiplex construction behaves more like a compressed version of larger developments. These projects involve tighter sites, stacked dwelling units, complex building code requirements, and significant mechanical, electrical, plumbing, and acoustic coordination within a relatively small footprint.
In cities such as Toronto, multiplex construction must also comply with the Ontario Building Code and evolving housing intensification policies. These requirements increase the importance of careful coordination between architectural, structural, and building systems.
When the designer and contractor are hired under separate contracts and brought together later in the process, the project inherits a structural weakness. The team creating the drawings is not the same team responsible for executing and sequencing the construction.
At 6ixDesig and 6ixBuild, we regularly encounter these challenges when working on multiplex and small multi unit residential developments. Our experience across architectural design, engineering coordination, and construction delivery reinforces a key theme. Many of the risks associated with multiplex construction are not caused by the building itself, but by how the project team is structured and how early coordination occurs between design and construction.
This article explains why these risks are particularly visible in multiplex construction, how integrated delivery models can reduce exposure, and what owners and developers can do when separation cannot be avoided.
How separation creates risk pathways
In a traditional design bid build process, the project moves through two distinct phases. Design occurs first, followed by construction procurement and execution. As explained by Infrastructure Ontario, this delivery model typically requires a completed design before a construction contract is awarded.
The Royal Architectural Institute of Canada also notes that this structure separates design and construction into independent contracts, which can limit early collaboration around cost, sequencing, and constructability.
This structure often generates several interconnected risk patterns.
- Coordination Failures and Constructability Gaps. If the contractor is not involved during the design phase, the design team’s assumptions about sequencing, tolerances, lead times, and trade access may remain untested until installation begins. Even with modern digital coordination tools, unresolved assumptions can surface as conflicts between structural, architectural, and mechanical systems once construction is underway.
- Communication breakdowns and frequent change orders. Unclear or poorly coordinated design information can quickly create problems during construction. In multiplex projects, where many details repeat across multiple units, even a small design ambiguity can multiply across the building and lead to significant cost increases and schedule delays.
- Responsibility and Liability gaps. Separated delivery models can also create disputes over responsibility. When conflicts arise between design intent and construction methods, project teams may disagree about whether the issue falls under design responsibility or construction methods. These responsibility gaps can slow decision making, increase disputes, and complicate accountability across the project team.
- Quality, Safety, and Defect Risk. When design and construction teams operate under separate contractual structures, quality management can become reactive rather than proactive. Designers may focus on documentation and approvals while contractors focus on schedule and cost control. Without strong integration, coordination issues may only become visible once construction work has already begun.
Why Integrated Design Build Reduces Risk
Integrated delivery models aim to reduce these risks by bringing design and construction expertise together earlier in the process.
In Canada, this structure is commonly formalized through agreements such as the CCDC Design Build Contract, where a single entity takes responsibility for both design services and construction delivery.
For multiplex developments, this structure directly addresses many of the coordination challenges described above.
Faster Project Delivery
Design refinement, procurement, and early construction activities can overlap rather than occurring strictly sequentially. This reduces the typical gap between design completion and construction start.
Greater Cost Certainty
A single contract structure reduces interpretation based extras and limits situations where design gaps lead to unexpected costs during construction.
Improved Constructability
Early input from construction professionals and trade partners makes it more likely that building systems, structural details, and envelope assemblies are buildable and coordinated before construction begins.
Clearer Responsibility
While legal responsibilities still exist for both design and construction activities, integrated delivery reduces the practical grey zone between design intent and construction execution.
Delivery Model Comparison
| Risk Dimension | Separated Designer and Contractor | Integrated Design Build |
|---|---|---|
|
Coordination and Constructability |
Constructability often tested after tender and issues discovered during construction |
Early collaboration improves coordination before construction |
|
Cost Certainty |
Budget finalized only after tender and the owner retains more risk |
Greater certainty through single contract pricing |
|
Schedule Reliability |
Sequential phases create handoff delays |
Overlapping phases can accelerate delivery |
|
Change Orders |
Ambiguities can lead to change order escalation |
Integrated teams reduce seam driven claims |
|
Responsibility for Defects |
Accountability may be split between design and construction |
Clearer single point responsibility |
|
Quality and Safety |
Quality management may become reactive |
Quality and safety planning integrated earlier |
Best Practices for Multiplex Developers
For owners and developers pursuing multiplex projects in Toronto and similar urban markets, one principle consistently proves important. Coordination should be treated as a deliverable rather than a byproduct.
If possible, align the procurement strategy with the risk profile of the building. Integrated delivery models allow teams to address constructability, coordination, and pricing earlier in the process.
When full integration is not feasible, project teams can still reduce risk by:
• requiring early contractor feedback during design
• establishing defined coordination milestones
• clarifying responsibility for system integration
• implementing disciplined change management processes
Municipal reviewers focus primarily on regulatory compliance and building code requirements. They do not resolve coordination conflicts between project teams. This makes early collaboration between design and construction especially valuable for multiplex projects.
