Architects and engineers ("AE") are the arbiters when projects involve formal specifications. The AEs determine whether a bid submission is specification-compliant before making an award. It is not unforeseeable that issues with construction arise from faulty design or construction. In such cases, who is at fault depends on how the mistake in design or construction was made. AEs are licensed professionals just like doctors and lawyers. There are clear repercussions when their design causes damage. When damage is caused by contractors or subcontractors, they are clearly at fault. They would be liable for damage caused to the premises.
AEs, like other professionals, are held to the standard of ordinary skill in the industry. In designing the specification, if the AE practices his or her profession below the standard of ordinary skill in the industry, and designs something that he or she should know causes an unreasonable risk of harm, that person subjects their company to liability when harm results. This would be determined through litigation.
The question of who is at fault is generally meted out during the discovery process. It is a fact-sensitive inquiry requiring specific information on the case at hand, as well as requiring the use of expert witness testimony to establish the standard of ordinary care in the industry.