Cabins give each individual ten cubic meters of space. On larger vessels private rooms are common. As ships get smaller, the number of crew packed into a single wardroom increases. Asari prefer shared spaces even on large vessels while krogan territorial instincts make it impossible for them to cohabitate even on the largest ships.
On smaller vessels, "hot bunking" is the norm. Crew members are assigned different watches share the same bunk. When one gets off-duty, he wakes up the person in the bunk. While that crewman is on duty, the first gets his rack time.
Spacecraft compartments can be isolated by air-tight doors in case of decompression. The cinematic version of explosive decompression is fiction; holed compartments either take enough damage that the occupants are killed instantly, or leak slowly enough that they are able to reach protective gear.
Compartments are equipped with Emergency Life Supports Apparatus: fireproof plastic bubbles with air bottles. Small when stowed, ELSA comfortably accommodate one individual inflated. Damage control procedure cuts off ventilation to burning compartments. Without oxygen to consume, fires die in seconds. The compartment is re-pressurized afterward for crew recovery.
Mass effect fields create an artificial gravity (a-grav) plane below the decks, preventing muscle atrophy and bone loss in zero-gee. Large vessels arrange their decks perpendicular to their thrust axis. The "highest" decks are at the bow, and the "lowest" decks at the engines. This allows a-grav to work with the inertial effects of thrust. Ships that can land arrange their decks laterally, so the crew can move about while the vessel is on the ground.
Warships normally turn off their a-grav systems during combat, reducing heat generated by systems and increasing combat endurance. To provide a point of reference for navigating in zero-gee, floors are painted a different color from the walls and ceiling.