The development of distributed real-time embedded systems presents a signi?cant practical challenge both because of the complexity of distributed computation and because of the need to rapidly assess a wide variety of design alternatives in early stages when requirements are often volatile. Formal methods can address some of these challenges but are often thought to require greater initial investment and longer development cycles than is desirable for the development of non-critical systems in highly competitive markets. In this paper we propose an approach that takes advantage of formal modelling and analysis technology in a lightweight way, making signi?cant use of readily available tools. We describe an incremental approach in which detail is progressively added to abstract system-level speci?cations of functional and timing properties via intermediate models that express system architecture, concurrency and distribution. The approach is illustrated using a model of a home automation system. The models are expressed using the Vienna Development Method (VDM) and are validated primarily by scenario-based tests.