A drainage member for use in promoting the drainage of water away from a substrate positioned adjacent the drainage member which includes an elongated, longitudinally extending base formed of a flexible material and having a plurality of outwardly extending projections. The projections are spaced from one another to form drainage channels between the projections. The elongated base has a plurality of expansion zones formed of the flexible material and extending generally transversely of the longitudinal extent thereof, the expansion zones comprising a deformation of the flexible material that absorbs longitudinal expansion of such material when it is exposed to heat without any significant increase in the longitudinal length of the drainage member.