Trim assembly and method of manufacture

A method of manufacturing a one-piece trim assembly for insertion in the interior of a wall opening adjacent to an exterior window assembly held therein, comprising the steps of:

• selecting pieces of solid cellular foam polyvinyl chloride or polystyrene corresponding to the dimensions of said wall opening to form jamb return members for covering at least a portion of an interior surface of the wall opening and casing members for covering at least a portion of an interior surface surrounding the wall opening;
• cutting both ends of said jamb return members and said casing members to a predetermined length;
• attaching the corresponding ends of said jamb return members together to form a jamb extension assembly;
• attaching the corresponding ends of said casing members to form a casing assembly;
• aligning said casing assembly on top of said jamb extension assembly;
• and
• affixing said casing assembly to said jamb return assembly to form a single one-piece trim assembly,
• whereby the one-piece trim assembly can be installed into a wall opening adjacent to the window assembly or the like independent of any additional structure.