Noah was exempted from the extermination. He was to build an ark, in order that he himself, his family, and the animals might be preserved. תּבה, which is only used here and in Exodus 2:3, Exodus 2:5, where it is applied to the ark in which Moses was placed, is probably an Egyptian word: the lxx render it κίβωτος here, and θίβη in Exodus; the Vulgate arca, from which our word ark is derived. Gopher-wood (ligna bituminata; Jerome) is most likely cypress. The ἁπ. λεγ. gopher is related to כּפר, resin, and κυπάρισσος; it is no proof to the contrary that in later Hebrew the cypress is called berosh, for gopher belongs to the pre-Hebraic times. The ark was to be made cells, i.e., divided into cells, קנּים (lit., nests, niduli, mansiunculae), and pitched (כּפר denom. from כּפר) within and without with copher, or asphalte (lxx ἄσφαλτος, Vulg. bitumen). On the supposition, which is a very probable one, that the ark was built in the form not of a ship, but of a chest, with flat bottom, like a floating house, as it was not meant for sailing, but merely to float upon the water, the dimensions, 300 cubits long, 50 broad, and 30 high, give a superficial area of 15,000 square cubits, and a cubic measurement of 450,000 cubits, probably to the ordinary standard, "after the elbow of a man" (Deuteronomy 3:11), i.e., measured from the elbow to the end of the middle finger.

Genesis 6:15 Parallel Commentaries

cubits.

Genesis 7:20 Fifteen cubits upward did the waters prevail; and the mountains were covered.

Deuteronomy 3:11 For only Og king of Bashan remained of the remnant of giants; behold his bedstead was a bedstead of iron...