The research is about systematic measurement of labour productivity to indicaternwhether construction labor productivity is low in the case of building projects inrnAddis Ababa, and if it is; to assess productivity problems and their causes.rnA review of other country studies, project reports and consultation with practitionersrnwere made to identify the productivity problem areas and process factors for inclusionrninto the study instruments. A case study of seven projects on three construction trades,rnnamely concrete, steel reinforcement placing and masonry works, revealed that 11rnfront line factors are responsible for low productivity; the major ones in the order ofrntheir rank are lack of materials, instruction delay, rework, change of workers, lackrnof tools and less work load and congestion.rnThe research result showed that nearly all projects (except project 5) have arnproductivity performance ability ratio (PAR) greater than one indicating that thernstudied crewsâ€™ productivity performance was low. In addition opinion survey ofrnforemen on the amount of effective productive time of workers showed that on thernaverage the studied craftsmen spend only 56% of the total paid time.rnAn open system theory of management was applied to identify the major managerialrncauses of productivity, which resulted in four factors contributory to low laborrnproductivity; these are: external precondition factors, technical management subrnsystem, managerial systems and organizational behavior factors. That is; Therncausal problems for low productive performance was analyzed and it was found thatrnunfulfilled conditions from project site external bodies, lack of project managementrnsystems, poor technical management in areas of developing productivity standardsrnand construction methods, average leadership efficiency and low project culturerntowards workers satisfaction are responsible for low productivity performance.rnKey words: process factors, open system theory, construction trades, performancernability ratio (PAR)