In ECOTECT, all planar surfaces have a normal from which their orientation is derived. You can display surface normals using either the Surface Normals or the Show Selection Normal items in the Display menu. This surface normal is derived from the direction of the nodes that make up the polygon, based on the right hand rule as illustrated in the image below. If you point the fingers of your right hand in the direction of increasing vertex indexes, then the direction your thumb points in is the same as its surface normal.

Object normals are important when calculating the orientation of faces for incident solar radiation, thermal analysis or exporting to other applications. Thus it is important to ensure that the surface normals of all exposed surfaces face outwards from the center of each zone to which they belong.

To Reverse an Object's Normal

To reverse the surface normal of any object, first select it and then click the Reverse Normals item in the Modify menu, or use the Ctrl+R keyboard shortcut.

You should the see the surface normal flip.

You can use also the surface normals of objects as a basis for selection. See the By Orientation items in the Select menu for details.

Things to note about surface normals

When a surface normal is flipped, the object's nodes are not reversed in memory. It simply sets a flag in the object that tells all the analysis and export routines that this object's nodes should be read backwards.