The construction industry across the world is characterized by inefficiencies, but the phenomenon of non-value-adding activities (NVAAs) has not been researched in the context of developing countries. The research aims to study the phenomenon of NVAAs, their causes, and their impact in public construction projects in Nepalese cities. A sample of 60 contractors, consultants, and government officials was interviewed to attain a 96.67% response rate, i.e., 58 participants. The results showed that the most common non-value-adding activities in human resources were "lack of required competencies," which was the most prominent, having the highest value of its relative importance index, 0.79, and "inadequate supervision," which had the second-highest value of its relative importance index, 0.78. The main causes include "lack of skilled workers" (RII=0.75), "poor planning" (RII=0.73), and "delayed design approval" (RII=0.73). Time and cost overruns (RII=0.78 and RII=0.75) were the most visible NVAAs. A strong consensus was found among stakeholders (correlations: 0.623-0.919, p>0.05). The study applies Lean Construction principles, recommending improvements in skills development, planning, and design approval, which could boost productivity by 15-20% and reduce time and costs in public infrastructure projects.