(Needs work obviously. Should it be combined with obstacles or no?) Barricading is a useful and often necessary way to keep the zombie at bay and give you some safety when trying to sleep.
You can barricade doors and windows with wooden planks each plank adding one third of a health bar, as well as create small and large fortifications using the Carpentry skill (n for a small fortification, Ctrl+n for a large one). Moving shelves, benches and chairs by (p)ushing them into door- or hallways can also work.
Barricading creates a buffer between areas with its own health bar, although relatively weak in the case of (b)arricaded doors or windows. Any zombie or survivor trying to get in needs to destroy the barricade on the door or window before they can enter or break it down.
When somebody starts bashing a barricade to get in while your character or any companions are sleeping, the noise can wake them up if they are near enough to hear it. This can be valuable as an early warning while resting or waiting out the night in your shelter. The chances of you waking up increase with each level of the Light Sleeper skill taken. You can only create barricades on closed doors and windows, each level of Carpentry you take increases the amount of "barricade health" that the door/object receives per barricade action.
Most buildings will contain something you can brea(k), creating planks for you to (b)arricade with. Large houses such as in the Residental District are poor choices of safehouses. While they're a good source of Planks due to furniture, their large size makes them very difficult to properly barricade and almost impossible to defend. Smaller 1-3 room homes are much easier to defend, and often contain at least one bed.