Komentarz do Diwrej ha-jamim II 3:7

And he overlaid - Heb. וַיְחַף like וַיְצַף, and he explains what he overlaid in the Housethe walls and the sideposts.

and its walls [i.e., the walls] of the sideposts of the House, which were [made] of stones, and he explains: “its walls and its doors with gold.” In I Kings (6:15) it says: “until the walls of the ceiling (קִירוֹת הַסִּפֻּן).” Now this is why he calls the roof קִירוֹת הַסִּפֻּן, because the roof was like an inverted ship (סְפִינָה) or boat, for it is customary to make the ceiling round, like a ship.