The old adage "shoemaker, stick to your last" has special applicability in the construction industry. This is because construction commonly involves three distinct disciplines: owners, designers and contractors.
From a legal liability standpoint, each of the three groups should refrain from performing functions of the other. Otherwise, the consequences may be serious.
For example, contractors should avoid making architectural or engineering decisions. Contractor's temptations to save either time or expense by unilaterally changing something in the work or making some deviation from plans or specifications frequently pose legal problems. If a contractor makes a design change without the approval (preferably written) of the architect or engineer, he runs the risk of being liable for faulty redesign.
Similarly, an architect or engineer who dictates the means, methods or techniques of construction may be held legally responsible for additional costs, delay or other expenses if his method proves unworkable. He may also be held liable for injuries to workers if the use of his means, methods or techniques results in accidental injuries.
In a recently decided case an owner-developer instructed his architect to disregard the recommendations of the soils engineer and directed the contractor to build a parking lot according to the architect's specifications notwithstanding the contractor's awareness that the specifications were inadequate. The parking lot failed. Predictably, the owner-developer lost the lawsuit. The appellate court ruled "Once the developer assumes control over the design and construction...he or she owes a duty of care in the exercise of that control." Fortier v. Dona Anna Plaza Partners, 747 F.2d 1324 (10th Cir. 1984).
A related problem is that one venturing outside of his own may be held to the legal standard of care required of an expert. Thus, a contractor who makes engineering decisions may be judged according to the skill and care required of engineers-even though he is not one.
The current AIA General Conditions (AIA Document A201-1976) requires the contractor to carefully study the contract documents and report any error, inconsistency or omission "he may discover" to the architect. However, there is no suggestion in that language that the contractor may make any necessary corrections himself-and he certainly should not!
Moral: Stick to your last or you may get stuck!