Much has been written on Off-site Manufacturing (OSM) in construction, particularly regarding the perceived benefits and barriers to implementation. However, there seems to be a wide misunderstanding of the state of OSM associated with the concept of decision by many of those involved in decision making process within the house building industry. This has led to a demand for guidance's on decision making process for construction project leaders particularly at early project stages. Choosing a construction method for a project will require an optimum decision strategy which involves careful understanding, measurement and evaluation of a number of decision factors that can have the most influence on successful decision action. This paper, therefore, aims to identify the key decision factors to be considered at evaluation stage when choosing to use Off-Site Manufacturing (OSM) as a construction strategy in house building projects. This will reveal the key drivers for change in the industry towards the use of OSM in house building.