Observatory access stair, view from the bottom looking into the attic.

The observatory stair has been capped with an insulated horizontal door to keep the house isolated from the attic space.  The door is balanced with a counterweight and pulley system and will stay in place wherever it is left.  The counterweight slides up and down the center 2x4 truss seen in the attic in the right image.  A conventional door will also be hung at the bottom of the stair leading into the control room.