Bryophytes are increasingly used in “green roofs” (especially in Europe), usually mixed with Sedum in prevegetated mats rolled onto roofs. In this paper, we briefly review the roof moss literature and also report our preliminary findings on voluntarily established roof moss communities near Terra Alta, West Virginia. We found 11 bryophyte species (including one liverwort) on four partly shaded roofs (differing in material, aspect, and pitch) that had apparently been relatively undisturbed for over 40 years. Species richness and composition varied considerably among roofs. The most frequent and abundant taxa were Hedwigia ciliata, Plagiomnium cuspidatum, Brachythecium laetum, and Platygyrium repens, each of which dominated a different roof. We suggest that Hedwigia merits further investigation as a candidate for extensive green roofs, based on drought-tolerance and a growth-form similar to that of Racomitrium -- which is used for green roofs in Japan. We hope that our review and preliminary data will encourage others to study roof mosses, which could potentially play an important role in the worldwide greening of cities.