Bridging documents

By Timothy Allinson, P.E.,
Murray Co., Long Beach, Calif.

Those of you with some experience in the design-build world are probably familiar with the term “bridging documents.” I have seen many sets of bridging documents come through my office — some are excellent while others are less so. To understand the purpose of bridging documents, a review of the design-build process is warranted.

In design-build project delivery the owner contracts directly with one entity to design and construct their project. The risk the owner takes is relinquishing some control over the design, but the reward is a typical savings of 6% in construction cost and a 33% faster schedule. Further, the design-builder assumes all of the design risk from the owner.

Frequently because of the nature of a project an owner cannot risk total surrender of the design to the builder. In such a case the owner will include with their request for proposal (RFP) a set of bridging documents that help define specific requirements of the project. The documents are usually prepared by a bridging architect and engineer who contract directly with the owner. These documents can range from performance requirements, or functional expectations, to prescriptive requirements, which are more specific and detailed. The more prescriptive the bridging documents, the more control the owner maintains, and the more risk he assumes. The use of bridging documents is often referred to as modified-design-build.

In the formal bridging process the bridging architect will prepare a schematic design for the owner’s benefit, often with input from the engineer but no formal engineering documentation. Once the architectural concept is blessed by the owner the bridging architect and engineer will prepare design development level drawings and a combination of performance and prescriptive specifications. This combination of drawings and specs, coupled with other legal documents, will make up the contract documents and will also serve as the design-build RFP.

The criteria as to what to include in the bridging contract is a fine line to draw. As the bridging engineer you should include all the design information necessary to protect the owner, but not spend time designing anything that can be determined by Code or the performance specifications. If you include too much you might inadvertently paint the owner into a corner; if you do not include enough you might not guarantee the quality and intent of the design. Plus, chances are the engineering fee does not include enough money for a fully developed design. If you don’t know the fee you should ask your boss how many labor hours were included for the engineering and try to stay within that budget. However, you should never let fee compromise the quality of your work. Sometimes fees are low for the sake of establishing a relationship, which makes it a marketing effort more than an engineering money maker.
It is healthy to have an understanding of the bidding process from the perspective of a bidding subcontractor in order to determine what to include on your bridging documents, should you be contracted to prepare them.

Once upon a time a bidding plumbing contractor would be given a full set of drawings and specs to properly bid a job, inclusive of all trades. Then when paper became expensive we would be lucky to receive a hard copy of the plumbing sheets and specs. These days we are usually just given a link to a website to download and print what we need, thus shedding the printing cost on us.

Putting that gripe aside, the plumbing documents should include at least enough information to understand the scope of the job, and should give particular attention to any unique attributes of the systems. When we print a set of the plans, they are given to various estimators to “take-off” the different systems, so there should be a drawing sheet to represent every (typical) floor in the building(s), if for no other reason than the estimator can highlight or draw-in the system piping for their take-off.

The other day my office received a set of bridging documents that were so incomplete we couldn’t even determine how many buildings there were from the plumbing set. The only way we knew there was more than one building was because the drawing title said “Building E.” That got us wondering about buildings A through D. It turned out there were seven buildings.

Often bridging documents don’t include riser diagrams, and this is an egregious omission, especially since the floor plans are never fully developed. Riser diagrams help the bidding subcontractors understand how the engineer expects the systems to be configured. They are a valuable use of time and paper — even though the engineer might think of them as intuitively obvious.

So, in short, a bridging package should include the following:

• A cover sheet with sufficient schedules to define the quality level of fixtures and equipment;

• A site plan that indicates utility connections and evidences there has been an initial pass at coordination with the civil engineer;

• Floor plans sufficient to quantify the number of fixtures and suggest the general pipe routing;

• For hospitals, locations of medical gas valve and alarm panels, as there is great room for interpretation as to the minimum requirements;

• Schematic details of any unusual program requirements. Example: we are bidding a job that has an interconnection between a set of pumps and an emergency water tank. The engineer did not define if the change-over to the emergency supply should happen automatically or manually, and there is a big cost difference between the two;

• It is not necessary to detail the piping of a typical toilet room — any good plumber knows how to do this. But if there is something unique and specific about how the owner wants the distribution piping run, then that should be defined. This can often be achieved with riser diagrams;

• Schematic riser diagrams should be included for each system showing general piping distribution;

• Typical details that serve to dress up the drawings are unnecessary, but details for non-typical elements should be provided. For example, we bid a job that showed a sewage ejector as 7'-6" deep. Further inspection revealed it actually had to be 23' deep! The engineer plopped a typical detail on their plans without giving it any real thought; and

• Lastly, try to think like a contractor (God forbid!) and define anything you can anticipate as being unclear. One hot water circulation pump per zone or two? Type, size, and quantity of water heaters? Is the water pressure known? Is a PRV rig required on the incoming service? And so on.

After the project is awarded the bridging engineer is usually retained to review construction documents prepared by the design-build contractor, shop drawings, and submittals. This process is not an opportunity to request anything of the subcontractor that was not defined in the bid. Remember that anything not defined in the bridging documents that is later requested in the review process will become the subject of a change order. Try to keep this in mind as you are preparing your bridging documents.

 

Timothy Allinson is a senior professional engineer with Murray Co., Mechanical Contractors, in Long Beach, Calif. He holds a bsme from Tufts University and an mba from New York University. He is a professional engineer licensed in both mechanical and fire protection engineering in various states, and is a leed accredited professional. Allinson is a past-president of aspe, both the New York and Orange County Chapters.