Abstract: A relatively simple log for use in log buildings includes a first large, longitudinally extending, V-shaped groove in the top of the log, and a pair of smaller longitudinally extending, inverted V-shaped grooves in the bottom of the log on opposite sides of a plane through the longitudinal axis of the log and through the vertex of the top groove, the spacing between the second grooves being such that outward extensions of the sides of the top groove in one log would intersect the outer sides of the second grooves in a superjacent log resting on such one log. In a wall structure, loose insulation fills the top groove and denser sealing insulation fills the smaller, bottom grooves.