As projects become more complex in their design and construction, coordination and use of project tolerances becomes more critical.
Construction tolerances are defined by the appropriate standard that specifies to what level of measurement the work is to be performed. Generally for concrete commercial and private work, the standard is ACI 117, Specification for Tolerances for Concrete Construction and Materials. For reinforcing steel, contract documents may refer to tolerances in both ACI 117 and in the CRSI Manual of Standard Practice.
The need for the coordination of tolerances becomes especially important when many different construction specialties are involved in a complex structure. On such projects, the work is broken up into separate work packages. This can result in a lack of understanding by subcontractors of the tolerances for their own work and the compatibility of those tolerances with other activities. On more complex projects, it is critical that all work be installed according to the tolerances for each specialty.
In the project specifications, owners and construction managers often include language that requires a subcontractor to measure and verify a previous contractor’s work. The subcontractor can’t always know the extent of this requirement at bid time, creating a difficult bidding problem. Does the subcontractor include costs as well as time in their schedule to perform this task? Or does the subcontractor assume, often incorrectly, that this work is the task of the construction manager or general contractor overseeing all of the work?
CMs and GCs will try to pass these responsibilities and the inherent risk on to subcontractors, making the subcontractors responsible for verification of work over which they have no control. To account for this, subcontractors would benefit by including an alternate in their bid package for both the cost and schedule impact of providing verification of a previous contractor’s work. Even if this alternate is not accepted, it would show clear intent that the subcontractor considered this as extra work and not part of the base bid package.
Because GCs and CMs use separate bid packages, different subcontractors are erecting formwork, fabricating reinforcing steel, placing reinforcing steel, and placing and finishing the concrete. With the GC or CM providing layout control for all of these different subcontractors, conflicts may result as internal tolerance compatibility issues arise with each of the various trades completing the concrete work.
When work packages are separated, it is incumbent upon the GC and CM that they take responsibility for ensuring that internal tolerances for each trade are considered properly. When the GC and CM perform the layout on a project and require all subcontractors to use that layout, they need to ensure that the provided layout allows subcontractors to perform their work within the tolerances as stated by the contract specifications.