A force-driven generative grammar rule is proposed as a design exploration method for planar networks in static equilibrium within non-convex domains. The aim is to enrich the catalog of unconventional structural typologies. Empty or partial networks in equilibrium are used as the starting point of the process. The rule’s successive application always leads to complete networks but ensures static equilibrium throughout the process. Overall, it operates as a form-finding engine for planar trusses and helps designers to gain knowledge and develop intuition about structural design. A number of case studies highlight the factors that affect: the number of iterations, the exploratory power, as well as the additional parameters that are required to apply a rule. Extension of the method to more general applications is eventually suggested.