Generally players will create a tight wall off with there naked barracks (no add-ons) and once they are ready to build a tech lab or reactor they will lift off the barracks and land it with enough space (add-on facing the ramp).
While this is more vulnerable then other spawn positions where your add-on is on the other side of the barracks, it still provides you with a tight wall off and is better than nothing.
Specifically in the 1-1-1 build you mentioned. Because there is so much add-on switching going on, it is possible to have either your factory or starport (depending on what units you go) building your extra add-ons. Most players also throw down a second barracks shortly after as well (which can also help build add-ons)