Diaphragms are typically horizontal but can be sloped in a gable roof on a wood structure or concrete ramp in a parking garage.
The diaphragm forces tend to be transferred to the vertical resisting elements primarily through in-plane shear stress.
The diaphragm of a structure often does double duty as the floor system or roof system in a building, or the deck of a bridge, which simultaneously supports gravity loads.
On the other hand, rigid diaphragms transfer load to frames or shear walls depending on their flexibility and their location in the structure.
Diaphragms that cannot be classified as either flexible or rigid are referred to as semirigid.