Static Edges are those which are not linked to any walls. Even if you draw a static edge along a wall, it will not move if you move the wall. A static edge is fixed in space. To create a static edge, click on any of the line tools available.

You can now create edges similar to how you create walls. First click where you want the starting point of the edge to be. Now move your mouse, and a line will start forming. Once you reach the end point, click there again and the edge will be created.