Example aspects of a retainer clip for a compression post, a compression post for a building, and a method of adjusting a length of a compression post are disclosed. The retainer clip can comprise a retainer body defining a first lateral body end, a second lateral body end opposite the first lateral end, a retainer opening formed through the retainer body and positioned between the first and second lateral body ends, and a retainer tab extending into the retainer opening; a biasing element positioner extending from the second lateral body end, the biasing element positioner comprising a positioner end wall, the positioner end wall defining an inner surface; and a biasing element engaging the inner surface of the biasing element positioner.