In architecture , a bay is the space between architectural elements, or a recess or compartment. Bay comes from “Old French baee,” meaning an opening or hole.


  1. The spaces between posts, columns, or buttresses in the length of a building, the division in the widths being called aisles . This meaning also applies to overhead vaults (between ribs), in a building using a vaulted structural system. In timber frame buildings a bay is the space between posts in the transverse direction of the building and aisles run longitudinally.
  2. A recess in a wall, such as a bay window
  3. The space between joists or rafters, a joist bay or rafter bay.