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MEP BIM services
7 October 2019
Kuldeep Bwail

How Contractor’s Design Portion (CDP) Fits into the Construction Process

Every link in the chain of the construction process is vital. One such link is the contractor’s design portion (CDP). The CDP comes into play when consultants on a construction project do not or cannot provide BIM models for audiovisual (AV) systems, security, sound masking, etc. Project contractors then require specialist entities or consultants to provide these electrical design services, or other services, so that these systems can be coordinated with the existing MEP (M&E) design or with other disciplines.

So, how do we understand what CDP is?

The CDP in a project is an agreement, or assurance, or contract by the main contractor to design certain portions of the construction. The main contractor can choose to create these designs with in-house expertise or procure the design work from specialist subcontractors. The work thus completed may include detailing work by specialist manufacturers and installers also. It is important for the main contractor to make sure that the various specialist designs contributed by various subcontractors are coordinated.

For example, if a suspended ceiling needs to be installed, the relevant subcontractor must know the details of the grid system and where the fixings should be for the suspended ceiling. Also, the details of space available above the ceiling for access for maintenance must be provided to the subcontractor. Design managers can help communicate and coordinate these details.


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Some features of the CDP process are as follows:
  • Building regulations approval must be procured by the main contractor for any subcontractor designs.
  • Project design consultants must determine at what point their design is shared with specialist subcontractors for completion.
  • Clarity in communication is vital for what the specialist subcontractor is required to provide. Function, form and quality must be described accurately in a performance specification.

In projects where building information modelling (BIM) technology is used, sometimes the CDP process may be disturbed or even eliminated. If a fully integrated, coordinated model of the building has been created at the time of the appointment of the main contractor, the model may not necessarily be given to the contractor. The client’s design team may prefer to retain control of the model. Now, specialist subcontractors must collaborate with whoever is managing the BIM model. In such cases, where BIM models including MEP designs have been created by design consultants, specialist subcontractor designs may have to be used in the pre-construction design stage rather than the construction stage.

Thus, when the design team works with the subcontractor designs at the pre-construction stage, tendering contractors must adopt specialist subcontractor designs within the tender offer. This means that the main contractor’s bid will include the specialist subcontractor design’s scope, price and programme in the main contractor’s bid.

Though a variety of services may be included in the CDP gamut, more common systems for which BIM models are provided by specialist subcontractors include audiovisual (AV) systems, security, sound masking, etc. Subcontractors need to provide several services for these systems. Here’s an overview:

What AV Design Consultants (Subcontractors) Need to Provide:
  • AV Functional capabilities, designs and budgets need to be developed.
  • Project requirements must be defined with a written specification and bid form.
  • AV system design must be coordinated with the project team
  • Complete system design package, with system drawings, specifications, equipment lists, etc. must be developed.
  • AV room layout and elevation drawings with critical dimensions must be developed.
  • Connection-level drawings for video, audio, control, LAN must be created.
  • Sound reinforcement systems must be configured.
  • Cabinet layouts, equipment rack elevations, jack field layouts, etc. must be designed.
  • AV Systems must be tested and commissioned to ensure system functionality.
  • Punch List documents must be prepared and followed up.
  • Client/user training assistance may need to be provided.
  • Networked AV devices must be coordinated with the client’s IT team.
  • Electrical circuiting, conduit and architectural work requirements must be identified as part of the final design.
  • Special instructions to the bidders must include details of relevant equipment, engineering, project management and AV Integrator installation services and supervision of cable contractor.

Productivity and accuracy in design and construction is improved by using BIM technology. Using BIM services can help generate realistic feedback on the functioning of security systems. Individual system devices can be located using BIM models and coordinated with other devices to ensure that all devices are correctly placed, connected and performance can be analysed. The security system can be integrated with the other operating systems in the building, so that the contractor can determine how the security system and devices relate to the spaces they occupy, the people they serve and the activities they enable.

Ideally, security (CCTV/Access Control) design subcontractors should provide the following:

  • Bid documents with supporting drawings and a bid form for submission to qualified vendors
  • Proposals evaluations, providing comparative bid analysis and recommendations
  • Shop drawing submission reviews

These services are subject to access control and CCTV monitoring requirements.

Similarly, sound masking design subcontractors should ideally develop the following:

  • Sound masking system requirements in conjunction with the project team
  • Sound masking floor plans and drawings
  • Bid documents and supporting drawings, with bid form
  • Shop-drawing submissions

The use of BIM models in MEP BIM services improves visualisation, productivity, coordination of installation documents, speed of project delivery and reduces costs. Specialist design consultants can benefit from the capability that BIM designs have for coordination and deliver a high-quality, cost-effective system. Conflicts are eliminated before installment, resulting in fewer modifications and delays.

The CDP part of the construction process can be made easier and more cost effective with experienced and technically certified human resources for main contractors in the West. Proficiency in AutoCAD and Revit that MEP Consultants in India possess, combined with their ability to read and understand construction and related documentation, makes MEP (M&E) design services sourced from India a preferred option for Western firms seeking to ease the contractor’s design portion of the construction process.