Abstract: A corner piece used in cooperation with retainer strips and exterior siding provides improved protection to a wall of a structure, particularly around rectangular openings in the wall. The corner piece includes a first section extending in a first direction along a first side of the opening and a second section integral with the first section. The second section extends in a direction substantially perpendicular to the first section along a second side of the opening adjacent the first side. The first and second sections form a continuous channel that extends into the retainer strips. A first retainer strip may be received within the first section and the second section of the corner piece may be received within a second retainer strip. As a result, the channel formed by the first retainer strip overlaps a portion of the first section and the channel formed by the second section of the corner piece overlaps a portion of the second retainer strip.