I'm making a hole in the wall using the Boolean function and my success is tenuous at best. It fails and looks crappy initially, but renders fine.

In the prep phase, I created a wall and an object to be used for the boolean operation.



I pushed the "green object" through the wall so that it intersects completely.



I selected the wall, THEN the green object and chose Mesh > Boolean > Difference and voila! ... a hole. But appearances can be deceiving as I have just created an n-gon that contains many edges and results in non-quads. There is a fix though...



I selected the faces around the inside of the hole and delete them.



I then selected an edge or two and then from the menu chose Select>Select Contiguous Edges but had to double-check to make sure the entire edge was selected.



Then I chose the Edit Mesh>Extrude command and pushing inward on the Green Arrow, I created a slight bevel.



I chose Extrude again and immediately switched to the Move tool and pushed the edge backwards until the edge was aligned with the back of the wall.



I created yet another bevel to close the gap...



I merged the paired-up vertices to complete the operation.



This is the result! I've performed this operation a half-dozen times, being careful to keep things clean, but the result is the same each time. The kicker is, it looks perfectly fine when it's rendered.

BUT, if I use the Mesh>Smooth command it ruins the hole and rendering no longer works. Is this everyone else's result? If not, what am I doing wrong?