Genesis 6:16

A window shalt thou make to the ark, and in a cubit shalt thou finish it above. The Hebrew text here indicates that an arrangement was made by which light and air could enter the ark, a light-opening, either under the ridge of the roof on one side, extending the entire length of the vessel a cubit in height, or in the upper deck, thus affording the opportunity for various light-openings in the interior. And the door of the ark shalt thou set in the side thereof. This was the entrance which the Lord afterwards closed, opening it again only at the end of the Flood. With lower, second, and third stories shalt thou make it. There were no individual openings for all these, but they were connected on the inside, probably by stairways, thus affording access to all the cells.