#4 - Design-Bid-Build Method (Part -1)

A significant percentage of buildings are built using the Design-Bid-Build (DBB) approach. The two major benefits of this approach are more competitive bidding to achieve the lowest possible price for an owner, and less political pressure to select a given contractor.

In the DBB model, the client or owner hires an Architect, who then develops a list of building requirements (a program) and establishes the project's design objectives. The architect proceeds through a series of phases: Schematic Design, Design Development, and Contract Documents. The final documents must fulfill the program and satisfy local building and zoning codes. The architect either hires employees or contracts consultants to assist in designing structural, HVAC, piping, and plumbing components. These designs are recorded on drawings (plans, elevations, 3D visualization), which must then be coordinated to reflect all of the changes as they are identified. The final set of drawings and specifications must contain sufficient detail to facilitate construction bids. Because of potential liability, an architect may choose to include fewer details in the drawings or insert language indicating that the drawings can not be relied on for dimensional accuracy. These practices often lead to disputes with the contractor, as errors and omissions are detected and responsibility and extra costs reallocated.

Stage two involves obtaining bids from general contractors. The owner and architect may play a role in determining which contractors can bid. Each contractor must be sent a set of drawings and specifications which are then used to compile an independent quantity survey. These quantities, together with the bids from subcontractors, are then used to determine their cost estimate. Subcontractor selected by the contractors must follow the same process for the part of the project that they are involved with. Because of the effort required, contractors typically spend approximately 1% of their estimated costs in compiling bids. If a contractor wins approximately one out of every 6 to 10 jobs that they bid on, the cost per successful bid averages from 6% to 10% of the entire project cost. This expense then gets added to the general and subcontractors' overhead costs.

The winning contractor is usually the one with the lowest responsible bid, including work to be done by the general contractor and selected subcontractors. Before work can begin, it is often necessary for the contractor to redraw some of the drawings to reflect the construction process and the phasing of work. These are called general arrangement drawings. The subcontractors and fabricators must also produce their own shop drawings to reflect accurate details of certain items, such as precast concrete units, steel connections, wall details, piping runs, and the like.

The need for accurate and complete drawings extends to the shop drawings, as these are the most detailed representations and are used for actual fabrication. If these drawings are inaccurate or incomplete, or if they are based on drawings that already contain errors, inconsistencies, or omissions, then expensive time-consuming conflicts will arise in the field. The costs associated with these can be significant.

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Article continued in - #5 - Design-BId-Build Method (Part -2)