A construction element is provided for forming a corner of a surface of a building, the surface including wall panels attached to framing studs. The construction element includes: a corner-forming surface that that is shaped to extend, in a cross-sectional view, between two separate wall panels, such that ends of the corner-forming surface, as viewed in the cross-sectional view, substantially match respective corners of the wall panels; and a fastener strip that, in a state in which the corner-forming surface is in its installed position with respect to the framing studs, is substantially parallel to one or more of the framing studs, such that a fastener can attach the fastener strip to one or more of the studs without passing through the wall panel.