Abstract: A simulated log siding for a cabin, house or other building is disclosed which can be constructed of tree heartwood, such as oak, or vinyl plastic. In the heartwood species, elongated planks are provided which have an outwardly bowed outer facing surface and a fiat inwardly facing surface. Each plank contains a notched inwardly facing lower edge and a rail extending along an upper edge of the outwardly bowed surface. The rail of a lower row of such planks inserts into the rabbet joint of an immediately adjacent upper row of such planks to provide a moisture barrier between adjoining rows. In the vinyl plastic species elongated planks are provided which also have an outwardly bowed outer facing surface. A flat panel is attached along an upper edge of the bowed surface which contains an outwardly projecting, downwardly opening catch channel or member.