Benefits and Challenges of Design-Build - Design-Build for Water and Wastewater Projects - page 11

Schedule

One of the most cited benefits of DB is the potential to reduce the project schedule. The
schedule savings can come from eliminating the bid phase associated with the more tradi-
tional DBB project delivery method and from the overlapping of the design and construc-
tion phases (Figure 2-2).
Some of the first research studies to document the time saving benefits of DB were
performed for vertical structures (i.e., buildings) and transportation projects. Although
the infrastructure elements and performance requirements for water and wastewater proj-
ects differ from those of vertical construction or transportation, the approach of having
design and construction performed by the design-builder and the project execution tasks
are similar. These studies found that construction speed for DB projects was 12 percent
faster than for DBB projects and total project delivery speed was at least 30 percent faster
than for DBB project (Table 2-1). In a similar study of transportation projects, DB was
found to reduce overall project delivery time by 14 percent (Table 2-1).
Likewise, in a study specific to water and wastewater facility projects, DB projects
were found to have significantly shorter schedules and less schedule growth than design-
bid-build projects (Table 2-2). The median schedule duration for DB projects in the study
was 23 months compared to 40 months for DBB projects. In terms of schedule growth,
design-build project schedules grew (i.e., the difference between the original contracted
duration and the actual duration) by half as much as DBB project schedules (i.e., 1 month
for DB projects versus 2 months for DBB projects).
It is the integrated project delivery approach of DB that promotes schedule savings
by allowing construction to begin before the design is complete. Because the designers
and constructors are part of the same team, there is no need to develop 100 percent
design drawings for bidding purposes. Depending on the level of detail necessary and
the requirements of permitting agencies, construction can begin before design is fully
detailed, thus resulting in time savings for DB projects.

Design-Bid-Build
Sequence

Design Bid Construction

Potential
Time
Savin gs

Design-Build
Integration

Design

Construction

Bid phase elimination and single
contract allow for integration of
design and construction

Figure 2-2. Potential time savings with design-build