Small elements are changed such as plants and the door numbers
Noted here: How does ‘The Big Bang Theory’ staircase work?
However, in reality, there is only one hallway-staircase set on Stage 25 on the Warner Brothers lot (a separate set is available for the lobby, which connects to the stairs).
When scenes involving multiple floors are filmed, the ...
Yes, there are several exits.
In S05E14 (Stress Relief, Part 1), Dwight stages a fire and everyone tries escaping. During this scene, once they notice the "fire" they attempt a total of four exit doors.
After they try those doors and have no luck, Michael freaks out and yells, "okay we're trapped, everyone for ...
Sunken living rooms were very popular in houses built in the 1960s and 70s, where they are often used in open plan designs to create "rooms" without walls, or to add ceiling height without raising the roof level.
They define the space. Sunken spaces are great for large, open concept homes. When walls are few, having rooms on a lower level clearly ...
Yes I know for sure there is a backstair case. Here is a clip of Dwight dragging Stanley from the annex through a hallway in the back down a staircase that leads to the front door of the building downstairs.
I found the answer in this wiki post:
The sets are always excellent, with wonderful attention to detail, the work of Production Designer Jerry Wanek and Art Director John Marcynuk. [...] Jensen said of the motel rooms: "Jerry Wanek's just a crazy guy, and likes to use his talents when he gets the ability to, and the motel rooms are his passion.
As you can see from the image gallery when searching "Lighthouse Interior", there are many which share the same staircase feature.