ABOUT TIME LOL
Eric Williamson, Design Lead for Fortnite Battle Royale, has announced in a new post over on Reddit that Fortnite v7.20 will feature a change to combat walls being built partially into the ground, as seen in the thumbnail. This happens particularly often in areas surrounding the main river, but can be found all across the map and has frustrated players since the launch of the game, so it's nice to see a fix finally being introduced. Here's a before and after of how it's going to work. As you can see, when a wall is partially underground, an additional wall will also be built on top of that one free of material cost. According to the blog post: "This feature will kick in when you attempt to place a structure edit: wall that: Requires a connection to a building piece The connecting piece is at least 70% underground Under those circumstances, the required connecting piece will now build automatically and for free. In addition, the connecting piece will inherit team ownership rules (and the material type) of the desired piece."
Before Patch v7.20
After Patch v7.20 They haven't yet decided whether this will apply to stairs eventually, but it won't with Patch v7.20. SOURCE: Reddit