Project Zomboid Spawning Airlock explained

It’s a bit of an understatement to say that Project Zomboid is a fairly gimmicky game in some respects. Not in a bad way, of course, because it wouldn’t be nearly as popular as it were. The way it handles spawning, for example, isn’t apparent at all at a glance.

While you can disable zombie (re)spawning during the Sandbox scenario creation process, the default state of the game is such that it eventually replenishes the undead populations after you’ve culled them. This may take longer or shorter periods of time, but they’re probably going to come back around sometime down the line. If you’ve already got an awesome base going, you may not care about this all that much, but there’s a catch: zombies can technically spawn within your base if you’re not careful.

This is due to the way Project Zomboid measures the passage of time and its relationship to zombie spawning. Notably you need a proper spawning airlock to make it impossible for zombies to spawn in your base. Sounds complicated, I know, but it’s really quite simple in practice.

How to create a spawning airlock in Project Zomboid

Spawning airlocks are one of those tricks that all the Project Zomboid veterans know and appreciate, but newcomers end up learning about the hard way. To understand what I’m getting at, it’s important to first understand two features of the game itself:

• Project Zomboid respawns zombies and processes their overworld migration based on ticks (i.e. backend passage of time).
• Zombies in Project Zomboid cannot respawn in blocked-off sections of the overworld.

Here’s the jig: simply blocking everything off will indeed work. However, you do need to open a door, gate, or fence to move through it. This process takes even longer still if you need to drive a vehicle through your entryway, and the more ticks pass by with your entryway open wide, the better the odds of the game pushing some zombies into your base.

To alleviate this problem, you just need to build a simple spawning airlock. Here’s a concrete example of me scrapping one up to quickly secure a temporary base of operations:

The picture featured above shows the default metal chain-link fence that was in place when I drove in. It’s the kind of gateway most military and penitentiary installations have in Project Zomboid, and it works well enough to keep zombies out of your hair. To set up a totally foolproof spawning airlock, though, you need to add an extra protective chamber with its own set of doors in front of the original fencing setup. Like so:

This is, of course, just a tiny spawning airlock meant to illustrate my point, but the goal is simple: you want to pass through a door, close it back up, and only then are you supposed to open the gate that actually leads out of your base.

Doing this makes it so that there’s never an opportunity for the game to spawn zombies within the perimeter of your closed-off base, as not a single tick passes by where there’s an open path from the overworld proper to your base. Neat! And easy to pull off, too, so there’s no excuse for you not to have a spawning airlock wherever you settle in Project Zomboid.

These rules may well change as we move into Build 42 and beyond, of course. We now know, for example, that zombies will finally be able to tear down metal fences, which will massively revamp how we set up our bases. That, however, is a problem for some other time, and it’s unlikely the practice of creating spawning airlocks will go away anytime soon.