Albert Barnes Commentary 1 Kings 6:34

"and two doors of fir-wood: the two leaves of the one door were folding, and the two leaves of the other door were folding." — 1 Kings 6:34 (ASV)

Fir-tree — Rather, this refers to juniper (see the note on 1 Kings 5:6). Each door was made in two parts, which folded back one on the other like shutters by means of hinges. The weight of the doors no doubt made it inconvenient to open the whole door on every occasion.