This paper deals with solutions to the equationis the unit ball in R N , N ≥ 2, and u + := max{u, 0}, u − := max{−u, 0} are the positive and the negative part of u, respectively. We extend to this class of singular equations the results recently obtained in [24] for sublinear and discontinuous equations, 1 ≤ q < 2, namely: (a) the finiteness of the vanishing order at every point and the complete characterization of the order spectrum; (b) a weak non-degeneracy property; (c) regularity of the nodal set of any solution: the nodal set is a locally finite collection of regular codimension one manifolds up to a residual singular set having Hausdorff dimension at most N − 2 (locally finite when N = 2). As an intermediate step, we establish the regularity of a class of not necessarily minimal solutions.The proofs are based on a priori bounds, monotonicity formulae for a 2-parameter family of Weiss-type functionals, blow-up arguments, and the classification of homogenous solutions.