There will be houses in one area.
Also i think some people will ask this, "Would the server lag from that amount of zombies?"
I though about this for awhile and came up with a solutution. Since my server can only take around 20 zombies at a time without serious lag, i devised a system to trigger zombies to spawn when you enter an area/room. Its like a power grid, but it controls zombies/lights/emitters.