International audienceWe study billiard dynamics on non-compact polygonal surfaces with a free, cocompact action of Z or Z(2). In the Z-periodic case, we establish criteria for conservativity. In the Z(2)-periodic case, we study a particular family of such surfaces, the rectangular Lorenz gas. Assuming that the obstacles are sufficiently small, we obtain the ergodic decomposition of directional billiards for a finite but asymptotically dense set of directions. This is based on our study of ergodicity for Z(d)-valued cocycles over irrational rotations