The Barn is a two floor building. A staircase connects the two floors. The second floor uses much less space than the first floor; it looks out onto the first floor, with a balcony overseeing the first floor courtyard.
The downstairs contains desks for detectives in an open plan seating area. All the detectives have desks. It does not appear as if uniformed officers have desks at all.
The Strike Team's "clubhouse" is also on the first floor. The clubhouse has two doors: one opens onto the main floor, while the other opens to an exit. Both doors were removed by Lt. Jon Kavanaugh during Season Five, but were restored by Detective Kevin Hiatt in Season Six. The clubhouse also has small lockers used by Strike Team members.
The first floor also has "cages" with chain-link fences to hold people who have been arrested, and an evidence room staffed by an officer. There is also a small workout room with dumbbells connected to the main entrance.
The men and women's bathroom are also on the first floor. The men's bathroom broke shortly after the Barn opened, so both men and women used the women's bathroom until Captain Rawling fixed the men's bathroom in Season 4. The men's toilet clogged again in Season 5. (Trophy)
The hallway exiting the building is partially blocked by large vending machines that Detective Steve Billings had installed.
The upstairs contains an interrogation room, along with another room where interrogations can be watched over closed circuit television. The interrogations are also often taped onto video cassette, although this can be disabled from the interrogation room.
The Captain's office is also usually a large room on the second floor; Captain Rawling turned the Captain's office into a war room against the One-Niners, although Captains Aceveda, Billings, and Wyms all used it as their own office. Lieutenant Jon Kavanaugh also took over the Captain's office to coordinate his own investigation. Captain Billings had a leather couch installed in the office while he was captain; that couch is now used by Captain Wyms.
- Like the bathrooms throughout most of the series, the locker room is also co-ed.
- The name "The Barn" was created during the Season 2 Episode "Co-Pilot" by Det. Tom Gannon.