Wall sill assembly and wall construction having a wall sill assembly

A wall sill assembly for use in a wall construction comprising:

• a sill base member including:
• a base wall having an upper surface, a lower surface opposite the upper surface, and an inner end and an outer end opposite the inner end;
• an inner wall extending in a direction which is one of oblique and perpendicular to the base wall, from the inner end of the base wall;
• an extension interface extending in a direction which is one of oblique and perpendicular to the base wall, from the outer end thereof;
• and
• an extension sill member including:
• an extension interface coupling;
• an extension base wall extending from the extension interface coupling;
• and
• an extension end wall extending from the extension base wall opposite the extension base wall;
• wherein the extension sill member is positionable so that the extension interface coupling at least partially encapsulates the extension interface, with the extension base wall extending over a portion of the upper surface of the base wall, and with the extension end wall extending away from the upper surface of the base wall, in a spaced apart configuration relative to the inner wall.