Working through the best design for the performance of a system or building is not constructability.
Constructability optimizes the design so that performance is maximized while being cognizant of construction cost and schedule before construction begins and before the design is complete.
It seems that this should be something that is always done - why not optimize the design so that the construction costs are minimized and schedule is shortened?
Typically there are a few culprits that prevent a design team from encorporating proper constructability:
1. The design team that is low bid on the project doesn't have the budget alloted to iterate a design along side construction professionals
2. Based on historical precedent, the design team is relunctant to collaborate with construction professionals to ensure proper constructability
3. The project is fast tracked and major project milestones must be complete prior to seasonal changes
It is too valuable for an owner (in terms of cost savings and schedule duration) to pass up on constructability in the design phase, the culprits above can be countered with the following:
1. An increase in design budget will save the owner more money in the construction phase
2. Collaboration with construction professionals is done all throughout the construction phase, why not start the process early in the design phase to maximize value for the owner
3. If project milestones must be complete prior to seasonal changes, carry forward with first phases of construction while continuing to iterate design for constructability
This part of costructability is often thought of as the construction phase, though proper constructability will also assess and optimize execution prior to construction start.
Think for example if a building has a deep concrete foundation and it is critical for backfill and the above ground structural to be complete prior to the winter season. It may be a wash in terms of cost, and a huge net benefit in terms of schedule, to reinforce the foundation walls with additional rebar to be able to withstand backfill without shoring posts / above ground structural errected.
It is in the best interest of the owner to be mindful of the construction execution in the constructability phase prior to construction.
Certainly once the project is fully into the construction phase, optimizing execution is primarily the responsibility of the general contractor and it's no longer constructability - rather it becomes construction execution optimization. Though it is rare for a general contractor to take on a commercial project without some feedback along the lines of "Why did the engineers do this?" or "I wish the engineers would have done it this way!"
This is the type of scenario that constructability tries to eliminate or mitigate as much as possible, by including construction professionals early on in the design process with periodic and systematic reviews.
Optimizing coordination of the construction trades is the responsibility of the general contractor though their can be value added when the coordination is aided and assisted by the design team and the owner representative.
That being said, this section on optimizing coordination refers to the coordination between the design firm and the construction team during the construction phase, in the best interest of the owner.
As much as constructability prior to design can provide huge cost savings and reduce the duration of the schedule - it is nearly impossible to completely optimize the design and execution so that there are no hiccups in the construction phase. There comes a point in constructability where enough time and money has been spent iterating the design and optimizing the build, and it no longer is of net benefit of the owner to continue with constructability - constuction must begin. At this time, minimal discrepancies must be acknowledged as possibilities when moving into construction execution.
There is value for the owner in having an intermediary between the construction team and the design team during the construction phase in order to optimize coordination between the two teams. This is done so that design discrepancies can be addressed in a timely manner and so that the value/cost/schedule impact of each decision is evaluated to ensure maximum value for the owner.
As is the case with most issues in the construction phase, time is of the essence, and so optimizing coordination between the design firm and the construction team can add value to the owner by mitigating schedule impact - and can also help by mitigating cost impacts for design discrepancies.
Construability is working through the kinks of design early, while optimizing the construction execution, to lower the overall cost and minimize the schedule of a construction project. Constructability is the single most important element of a construction project and is the best opportunity to lower construction costs, improve the schedule, integrate sustainable design principles and impove the performance of the building.
Too often construction projects go ahead to construction without performing proper constructability in the design phase. It is because of this that we unequivocally recommended that any client considering a new build first consider incorporating constructability into the design-build process. Proper constructability can offset the incremental cost of going green - which maximizes the return on investment for the owner while being conscious of the environment at the same time.