Charles Ellicott Commentary 1 Kings 6:15

"And he built the walls of the house within with boards of cedar: from the floor of the house unto the walls of the ceiling, he covered them on the inside with wood; and he covered the floor of the house with boards of fir." — 1 Kings 6:15 (ASV)

Both the floor. —The true reading is that of the margin, agreeing generally with the Septuagint and the Vulgate: that from the floor to the walls of the ceiling (including in this phrase the surface of the ceiling itself) he covered all with cedar, and laid the floor with planks of cypress.