Your local building code will list all the framing requirements for whatever type of structure you're building. Most exterior walls require spacing of 16 inches on-center, while many non-load-bearing interior walls only require 24 inches of spacing. However, there are also varying requirements depending on your construction material, so checking your municipality's rules is essential.

Bump-out additions can add some space to a closet without requiring any significant structural work. This entails pushing back the existing rear or side of the closet, simply moving the wall into either an adjacent room or unused space. For ground-floor closets, this could even be extended to the exterior of the home, but that has its own complications. Bump-outs are a good discussion to have with your contractor if you’re just looking to increase the space a little—not renovate the entire closet space.

There are approximately 5.33 board feet in a 2x4. You can use the board foot calculator in this article to easily find the answer. A 2x4 is 2 inches of thickness by 4 inches of width, so you need to find the length, with 8 feet being the most common. You’d use the calculator here to multiply 2 times 4 times 8, and then divide by 12, arriving at a total of 5.33 board feet. 

Yes, you can find ceiling joists using simple tools if a stud finder isn't available.

Using a hammer requires patience and a keen ear. Gently tap the ceiling in a grid pattern, listening for sound changes. A hollow sound indicates space between joists, while a solid, dull thud suggests a joist. Mark the location with a pencil and confirm by tapping from different angles.

Alternatively, you can use a nail, but this method will leave small holes. You'll feel increased resistance when the nail hits a joist. Mark the spot and repeat the process every 16 or 24 inches to map the joist locations. This method is considered less reliable than using a stud finder.