Modern software systems are highly interconnected and have been under constant change for many years. IT decision makers find it difficult to predict and plan change projects due to the complexity of the enterprise systems. Thus, a large proportion of projects with the purpose of changing a software system environment fail, i.e. they tend to take longer time and cost more than expected. This paper suggests enterprise architecture as an approach to model software systems and their environment. An enterprise architecture metamodel for maintainability modeling and analysis is presented. IT decision makers can use this metamodel in order to make cost predictions and do risk analysis for their change projects.