Given the development of Additive Manufacturing (AM), popularly known as 3D Printing, the coexistence of AM and conventional manufacturing (CM) in AEC will be a reality for the foreseeable future. Case studies on two AM metallic building components demonstrated that AM for building components is technologically feasible but cost-prohibitive today, and, in some cases, has lower environmental impacts than CM. Firstly, a feasibility study was conducted to assess the applicability, time to manufacture, and manufacturing cost of AM vs. CM of specific metallic building components. Secondly, Life Cycle Assessment (LCA) was used to assess environmental impacts of AM and CM for those two cases. The case studies were the first well-documented comparative analyses of AM vs. CM for building components, and they contribute to the emerging "AM-in-AEC" knowledge base with their assessment approach, findings and documented baseline efforts for the analyses. The studies also revealed that AEC practitioners lack a systematic way to rapidly and consistently assess the applicability (A), schedule (S), environmental impacts (E), and cost (C) of AM compared with CM to produce building components. Future work includes formalization of such an ASEC multi-criteria framework and impact assessment of the formalized assessment process on the effort and the consistency of the assessment between different assessors.