Multi-piece polymer building products

A polymer building product, such as a vent, mounting block, etc., for mounting to the exterior of a building and concealing the edges of siding disposed adjacent the building product, the building product comprising:

• a base portion having an axial wall bounding a central area, and a flange for securing the base portion to a substrate, the flange extending outwardly away from, and oriented generally perpendicularly with respect to, the axial wall;
• a top portion including an axial wall bounding a central area, the axial wall dimensioned to be receivable over the axial wall of the base portion in lapped relation therewith, and a substantially continuous peripheral flange extending outwardly away from, and oriented generally perpendicularly with respect to, the axial wall, the peripheral flange dimensioned so as to conceal the edges of siding disposed adjacent the base portion;
• engaging elements disposed on the axial wall of one or both of the base and top portions for securing the base and top portions together when the axial wall of the top portion is telescopingly received over the axial wall of the base portion in lapped relation therewith;
• and
• wherein the axial wall of one or both of the base and top portions is configured so as to provide clearance between that axial wall and the engaging elements disposed on the other of the axial wall of the base or top portions when the base and top portions are mated in a first rotational orientation of the top portion relative to the base portion, and to permit the engaging elements to secure the base and top portions together when the base and top portions are mated in a second rotational orientation of the top portion relative to the base portion.