Hi, all!
As far as I can see, when you extrude a surface, it is actually moved, not copied. As a result the original surface ( the “base” ) is lost and if you need it you have to re-create it. So my question is : can you extrude a surface while keeping the original ?
Thanks in advance,
Thierry
a workaround to that is to select the faces that are going to be extruded
press SHIFT+D to duplicate them , then enter
The duplicated faces will be the one selected
Extrude those faces
Select all -> W -> Remove Doubles
And you’re done, the extrusion is done and the original faces are still there
Very nice, Sanctuary ! Seriously, I’d never thought of that 
Many thanks.
Ain’t you ending in non-manifolds by removing doubles?
Although Sanctuary has given you a way to do this you haven’t told us why you want to have this geometry. I for one see absolutely no use for this and can think of any number of serious problems down the line when you do this. Just a tip!