As a result, most common interior doors are the same height and range in width from 28 to 32 inches. The length of a door usually depends on its use and installation requirements. There are several types of common doors including sliding doors, folding doors, and double doors. Sliding doors hang on tracks and can be opened from inside or outside the house. Folding doors consist of two sections that fold together when not in use. Double doors have two separate panels that each go up a separate frame member. These are the most secure type of door because they require a key to open them from both sides. When choosing a door, it is important to consider how it will be used. If you need to lock up a storage room or make a closet accessible only by this one door, for example, then a single door that opens into a frame is all you need. But if you need to provide easy access from one part of the house to another, or from your home to the street, then multiple doors with different opening mechanisms may be needed. In addition to considering how the door will be used, you should also look at its appearance and feel.