Ambient temperature temperbead welding employs the gas tungsten arc welding (GTAW) machine process, and avoids both the elevated temperature preheat and postsoak heating operations associated with conventional temperbead welding. American Society of Mechanical Engineers (ASME) Code Case N-638 currently governs ambient temperature temperbead welding activities. N-638-4 limits the depth of an ambient temperature temperbead weld repair to 50% of the base material thickness. This restriction precludes use of the GTAW ambient temperature temperbead process for buttering of through-wall repairs and replacements. This paper describes the ongoing ASME activity to revise N-638-4 to permit through-wall temperbead repairs. The methodology, code text, applicable restrictions, and technical bases for Code Case revision N-638-5 are addressed.