The present paper addresses the problem of detecting closed compartments produced by a set of planar faces in the space. The topology of the set is general, and edges in the final piecewise planar surface can belong to one, two or more faces; boundary representations for non-manifold solids are particular cases. An octree structure (dubbed compartment Octree) that defines a 3D graph through the volume defined by the set of faces is proposed, and it is shown that a seed propagation algorithm on the graph can be used to detect the existing closed compartments. The algorithm can either compute the total number of compartments or detect if the set of faces define a closed solid volume, the outside part being considered as a separate compartment.