From the homeowner, 

"The barn wood did come off of my grandpa's barn that he built.  It was a horse barn.  My brother actually lives on the property now...

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...We saw the school doors in a parade home in Ada. They told us they were old school doors from Central High School in Grand Rapids.  In the house in Ada they were painted differently.  They had a medium to dark stain, and the grain of the wood was white.  They looked cool. When I brought the doors home and started sanding them, we liked the natural color of the doors.  Then we just decided to keep the natural color, and just put a matte polyurethane on them."