Necessary and sufficient conditions are obtained for the infinitesimal rigidity of braced grids in the plane with respect to non-Euclidean norms. Component rectangles of the grid may carry 0, 1 or 2 diagonal braces, and the combinatorial part of the conditions is given in terms of a matroid for the bicoloured bipartite multigraph defined by the braces.Theorem 1.1. Let G(B) be an m × n braced grid bar-joint framework in R 2 and let • be a differentiable, strictly convex non-Euclidean norm. Then the following are equivalent.() and the bicoloured braces graph of G(B) is a spanning subgraph of K 2 m,n with an independent cycle in each path-connected component. A simple graph is a cycle-rooted tree if there is an edge whose removal gives a tree, and is a cycle-rooted forest if each connected components is a cycle-rooted tree. We extend this tree and forest terminology to bicoloured multigraphs G whose monochrome subgraphs are simple. Thus G is a cycle-rooted tree if there is an edge whose removal gives a tree. The graph condition in (ii) means that the braces graph contains a spanning subgraph that is an independent cycle-rooted 2000 Mathematics Subject Classification.