Apartment 4A

Apartment 4A is the primary setting in The Big Bang Theory, and is apartment where Sheldon and Leonard live. It is situated in an apartment complex at 2311 N. Los Robles Avenue in Pasadena, California. The apartment, described by Howard as Nerdvana, is full of games, action figures and everything else that he considers cool.

It is located on the fourth floor of the building, and is located across from Apartment 4B, where Penny lives. 4A is known to be a corner apartment, being that it has windows facing outside on almost all sides.

Layout
The apartment has one living room, one bathroom and two bedrooms. A hallway links the the living room to the bedrooms. The kitchen is part of the main living area.

Immediately upon entering, the wall on the right houses Sheldon and Leonard's desks, as well as the TV. The wall ends in the kitchen part. This wall is rarely visible, being the wall that is the view into the apartment from which the episodes are filmed, and has only been shown on two occassions (one is in "The Euclid Alternative" [S2E05]). There is an unseen window on this wall, being that Sheldon likes to open it to create a cross breeze when he is sitting in his spot.

The wall immediately to the left after entering the apartment has a long bookshelf that ends at a small closet, with the wall itself ending at a large window with a desk and telescope. The City Hall of Pasadena can be seen from from this window, which has has been used on several occasions: in "The Tangerine Factor" (S1E17) Penny used it to throw her ex-boyfriend Mike's iPod out the window; in "The Panty Piñata Polarization" (S2E07) Sheldon shows Penny that he'd hung her clothes from a telephone pole outside; in "The Einstein Approximation" (S3E14) Sheldon throws a white board from the window, causing the sound of braking and car horns, implying that there is a fairly large road just down the window; in "The Ornithophobia Diffusion" (S5E09) a blue jay lands on the window sill outside, which upsets Sheldon.

After the window, there is a corner and the hallway that leads to the bathroom, as well as Sheldon and Leonard's bedrooms. The kitchen is a small area that has an island with rarely used barstools since they eat in the living room area.

Sheldon at one point in time had painted luminous arrows on the floor to show someone the nearest exit in case of an emergency during the night. He shows them to Raj in "The Roommate Transmogrification" (S4E24), but got rid of them before "The Friendship Contraction" (S5E15), when he explains that they are "wildly carcinogenic".

Production-wise, the bathroom interior, Sheldon's bedroom, and Leonard's bedroom are actually filmed on a different set than the rest of the apartment. The actual apartment set ends at a corner in the hallway immediately after the bathroom door. This is for easier filming access and better view of the actors for the studio audience.

The Bathroom
The bathroom has a double bath/shower. Sheldon and Leonard have a shower curtain with the periodic table of elements printed on it. Sheldon has placed a UV light box there to stop his toothbrush from being infected by germs as well as placing tape on the floor. The tape serves to avoid splatter on the mirror from flossing teeth, and to stop urine from getting on the floor when men use the toilet. Sheldon also has a squeegee to clean the mirror.

Sheldon's Bedroom
Sheldon's bedroom is located immediately after the bathroom. Sheldon usually keeps his bedroom locked, and rarely allows anyone inside.

Leonard's Bedroom
Leonard's bedroom is the last room in the hallway. There is a ledge outside that runs by both bedroom windows. Sheldon uses this during the episode "The Bozeman Reaction" to access Leonard's room because he was too paranoid to go out of his bedroom because of them being burglarized earlier in the episode.

History
In The Staircase Implementation, the story of how Leonard and Sheldon meet is revealed. We find out that Sheldon had placed an ad for a roommate after his former roommate was driven to the brink of madness from Sheldon's antics. Leonard encounters Sheldon's former roommate on his way to the interview with Sheldon. The roommate tells Leonard to run away. Leonard is accepted by Sheldon as his new room-mate and inherits the former roommate's room, only to discover that the roommate had painted "DIE SHELDON DIE" on the wall in red paint.

At this time, the apartment also had significantly less furniture in the living room. Sheldon's only placement was two lawn chairs and cinder blocks in which he placed the TV. Even at this point in time, Sheldon's lawn chair was placed in the exact spot that he claims later on the couch. Their first major addition in furniture to the apartment was the leather couch, in which Leonard buys for a hundred dollars from tenants on the first floor who were moving out.

In the episode "The Bozeman Reaction", the apartment got burglarized. Some of Sheldon and Leonard's game systems were stolen. The Police were also called to the apartment in the episode "The Zarneki Incursion", in which Sheldon's World of Warcraft account was hacked.

An apartment flag is mentioned in the episode "The Staircase Implementation", and is a small blue flag with a yellow coat of arms lion on it. Flipping it upside down signifies that the apartment is in distress.

List of known items in the apartment

 * Periodic table shower curtain
 * Hulk hands
 * Razer Orca headset
 * Master Chief helmet
 * Green Lantern Lantern
 * Various Comic Books
 * NES
 * SNES
 * N64
 * NGC
 * Nintendo Wii
 * PS1
 * PS2
 * PS3
 * X-Box
 * Xbox 360
 * Various Games
 * Leonard's high school yearbook
 * Sheldon's laptop
 * Leonard's laptop
 * Sheldon's whiteboard
 * Leonard's whiteboard
 * Gollum pencil holder
 * Leonard's bat signal
 * Dart board
 * Batman cookie jar
 * Microwave oven
 * Toaster oven (until it was destroyed by the guys' robot)
 * DNA molecule model
 * Amazon Kindle
 * Longclaw
 * Leonard's green light saber
 * Boba Fett Helmet
 * Sheldon's reverse osmosis machine
 * Sheldon's model trains
 * Sheldon's spot on the couch
 * Various action figures