Contractor Design Portions — commonly referred to as CDPs — are design packages that are transferred from the employer’s design team to the main contractor or a specialist subcontractor as part of the construction procurement. They represent one of the most significant areas of design risk on any construction project, and yet they are also one of the most inconsistently managed. When CDP submissions are reviewed properly, they protect the client’s quality and safety standards and reduce the risk of costly late-stage problems. When they are not, the consequences can be severe and difficult to recover.

On most construction contracts, some or all of the design is produced by the contractor or their specialist subcontractors. Understanding what the contractor is responsible for, and how to review their design submissions effectively, is an essential skill for any project manager or employer’s agent. Poor CDP review processes are a common source of defects, interface failures and contractual disputes on construction projects.

What Is a Contractor Design Portion?

A Contractor Design Portion is a section of the design that the contractor is contractually required to complete, rather than the employer’s design team. Under JCT design and build contracts, the CDP is the norm — the contractor takes responsibility for the whole design. Under traditional procurement, CDPs are used for specific specialist elements: structural steelwork connections, curtain walling systems, mechanical and electrical installations, precast concrete, cladding systems and the like. The extent of the CDP must be clearly defined in the Employer’s Requirements (ER).

Why CDP Reviews Matter

If the employer’s team does not review CDP submissions properly, several problems can arise. Poorly coordinated CDP designs can lead to expensive clashes on site. Non-compliant CDP designs may not be picked up until the work is installed, by which point remediation is costly and disruptive. The employer may also lose contractual protections: under most standard forms, if you approve a CDP submission without identifying a defect, you may be deemed to have accepted the design. The review process is also an opportunity to ensure the contractor’s design is properly integrated with the rest of the project.

What a CDP Submission Should Contain

A proper CDP submission should include design drawings at an appropriate level of detail for the stage of the project, a specification that describes the materials and systems being proposed, calculations where relevant (particularly for structural and services elements), evidence of compliance with the relevant standards and regulations, and a clear statement of any proposed derogations from the Employer’s Requirements. Incomplete submissions should be returned without review, with a clear request for the missing information.

How to Review a CDP Submission

The primary review task is to check that the contractor’s design complies with the Employer’s Requirements. The ER sets the performance specification, the standards and the constraints. Read the relevant sections of the ER against the submitted design, check the specifications and drawings, and assess whether the design meets the required outputs. Note that your role is to check compliance, not to re-design: if the contractor’s design is compliant, it should be approved even if you might have approached the design differently.

Check Compliance with the Employer’s Requirements

CDP elements rarely exist in isolation — they interface with other parts of the building and with other disciplines. When reviewing a CDP submission, check whether the contractor’s design will coordinate with the base-build structure, the MEP services, the facade and the surrounding work packages. Request federated model information where BIM is being used, and identify any spatial or technical conflicts before they reach site. Unresolved interface issues at the CDP stage are a significant source of construction claims.

Check Interface Coordination

A derogation is where the contractor proposes a design that departs from the Employer’s Requirements in some respect — typically because the ER requirement is unachievable, inappropriate, or because the contractor has a better solution. Derogations should be identified explicitly in the submission and assessed carefully. Approving a derogation has contractual implications: it may transfer responsibility for the departed element back to the employer. Any approved derogations should be formally recorded and, where significant, the ER should be updated to reflect the agreed change.

Assess Derogations Carefully

The review status should be recorded formally — whether that is A1 (Approved), A2 (Approved with Comments), B (Revise and Resubmit), or Rejected — and the contractor should be notified in writing within the contractually agreed timescale. Responses should be documented in the review comments, not just verbally. Maintain a CDP register that tracks the status of every submission, so that nothing is forgotten and the audit trail is clear.

Record the Review Status Clearly

JC Virtual PMs provides design management and document control support to clients and employers’ agents on projects with significant CDP elements. We can help you establish a clear review protocol, manage the submission and response workflow, and maintain the records you will need if disputes arise. Contact us to find out more.

How JC Virtual PMs Can Help