[Web(flash?)][~2000-2010] Game about defending an apartment from zombies

You had 2 other npc's in the house to help you defend it. They were positioned on different storeys. Each had a different gun. You could command them to some extent to change their positions.

The zombies would come from the left and right, break the barricades, and try to reach and break a radio/generator(?) positioned on the roof. Their behaviour wasn't that complex, they'd just climb the stairs to reach the device or chase you if you stood too close to them.

As the game progressed, you would unlock different upgrades like better guns or new/bigger apartments. You could also fix broken barricades. I think there was some kind of currency system to handle these.

The game had a side view of the apartment, where the inside was visible as if there was no wall (kind of like terraria). Although I am not sure, I think the game was pixelated. Either that or had very simple, unrealistic graphics.