Have you tried other lots included with this hood? A quick Google search informs that this hood is actually rather buggy.
I have tried one other lot and had no problems. I'll try out some of the smaller lots and see what happens.
Thank you very much for letting me know your search findings. I definitely must be doing something wrong as I haven't been able to find any useful reviews of/comments on this custom world. It's a shame to hear that it's buggy, I haven't found another custom world similar to it, but of course I'd rather know now than invest more time into it.
Stairs have always had problems when transplanted or saved and reloaded, like with a neighborhood. Try uninstalling and reinstalling the neighborhood.
In The Sims 2, when this happened, the stairs would only work in two cardinal directions- that is to say if they were broken on North/South (arbitrary terms since there's no true direction in-game), they'd work fine on East/West. Try building stairs on this lot facing the other way. If those work, that's the problem- and I don't believe there's a way to fix it, but I'd look it up to be sure.
Thank you for your detailed response. I'm not sure how to reinstall a neighbourhood but I will go away and figure that out.
Can I clarify whether 'broken stairs' is a term you are using to refer to steps with various glitches, or a complete inability to function? I ask because the ground floor staircase inside of the house is in the same cardinal direction (I hope I'm using that phrase correctly) as the broken stairs, but appear to work correctly.
Also, the original outdoor steps leading to the front door were split. It is difficult to describe, but if you were a sim with your back to the front door, in front of you would be steps going down in a forward direction. Once you reached a platform there would be a set of steps facing left and a set of steps facing right. They were facing opposite directions. Both the left and right set of steps had a platform at the bottom, off of which was another set of stairs each. Both of these were again turned to face 'forwards' (the same direction as if you headed straight out of the door) and would take you to the bottom of the slope.
I had actually wondered if having two sets of stairs, both with right-angle turns, was causing some of the problems. That's why I rebuilt the stairs into a simple forward-facing slope, as pictured in my first post, but I definitely don't recall the sideways-facing stairs as being any less broken than the forward facing steps. The stairs are more broken since rebuilding them, though.
I hope that makes some sense, thank you very much for your advice.