Albert Barnes Commentary 1 Kings 6:8

"The door for the middle side-chambers was in the right side of the house: and they went up by winding stairs into the middle [story], and out of the middle into the third." — 1 Kings 6:8 (ASV)

The door for the middle chamber - that is, the door that gave access to the middle “set of chambers.” The chambers on the ground floor were possibly reached by individual doors in the outer wall of the lean-to. The middle and upper floors were reached by a single door in the right, or south, wall; from there, a winding staircase ascended to the second tier, and another staircase went from the second to the third. This door to the stairs was in the outer wall of the building, not in the wall between the chambers and the temple. Placing it in the temple wall would have desecrated the temple far more than the insertion of beams.