Complex sentence: Part of the millwork in the house was mass-produced in that mill. It mainly consists of the Hall/Stairwell Wainscoting which pattern is also used in wainscoting for the 2nd Floor Bathroom.
Split into simpler sentences: Part of the millwork in the house was mass-produced in that mill. It mainly consists of the wainscoting in halls and stairwell. The same wainscoting pattern is also used in the 2nd Floor Bathroom.