Direct Answer
An RFI (Request for Information) is a formal written question submitted to the engineer or GC when the design documents are unclear, contradictory, or silent on a condition that affects fabrication or erection. You should submit an RFI any time you cannot confidently proceed without risking a wrong decision — never guess at design intent on a structural member.
Full Explanation
RFIs are formal contract documents — they create a paper trail of a condition that was not clear in the design, and the engineer's response becomes a binding clarification. An RFI should clearly state: what drawing(s) or spec section the question references, what the specific unclear or contradictory condition is, what the impact on fabrication is (can't proceed, affecting schedule), and optionally a suggested solution. The response from the engineer is typically issued as an RFI Response or clarification drawing.
What This Means for Your Shop
Every RFI you submit that results in a design change is potential change order documentation. RFIs are how fabricators protect themselves from scope creep and design errors that would otherwise be absorbed as rework. Maintain a complete RFI log and ensure every open RFI is resolved before the affected work is performed.
Common Mistakes
Making an assumption rather than submitting an RFI because 'it seems obvious' or 'it'll hold up the schedule.' Assumptions that turn out to be wrong are almost always more expensive than the schedule impact of an RFI.
Recommended Process
Establish an RFI template at project start. Submit RFIs as soon as unclear conditions are identified, not the day before you need to fabricate. Track all RFIs in a log, including the response date. Flag any RFI that remains open past its response deadline to the GC.