unexpected behaviour when extruding a plane mesh


I’m trying to learn blender using some of the great tutorials on the net. In one of these tutorials the author asked me to add a plane mesh, delete the face and extrude it to create a wall. But the constructed wall is open at the start. So we add back the face for the first 4 vertices.

Now I asked my self why delete the face prior to the extrusion. I tried and of course it worked. But the extrusion is now in the opposite direction (just typing e and a number). Opposite to the direction of the normal. I tried with a box. I selected a face and extruded it. As expected the new faces extend away from the box in line with the normal. I flipped the normals and now it extrudes into the box. As expected.

So why is a single face behaving differently?

Thanks for your answers.


I think the question is the facing of the normals after an extrusion? If you extrude in the direction of the normal, it will face inside the box, and the others will as well. Extruding away, or the opposite direction forces the normal to point outwards and the others will too. Typing e and a number forces the extrusion (in my test) to move in the opposite direction of the normal, preserving the outward direction. Typing a negative number forces the extrusion to follow the normal, forcing the other normals inward.

Don’t know if this helps.