Get Version 1.1!
The door is a dynamic object which will only open for friendly units. It can also be locked via the radial menu to stop friendly units from opening it. This is your cheap rickety Door weaker as the Door and the Reinforced Door but a lot cheaper.
The door must be built on flat terrain. It can be built on the ground, on bricks or on logs. The Door requires 3 Planks to be built.