Ruin

Ruined buildings are darker grey.

Introduction of Ruins

As per the 14 August, 2007 Update:

"Some of the more territorial zombies have taken to ruining buildings; ransacking a building to such a thorough extent that the damage is visible from the street. Ruined buildings can only be repaired by survivors with construction experience and a toolbox."

Creating a Ruin

A building must be ransacked five times for the option to ruin it to be available. Ruined buildings appear on the map as regular buildings, but with a darker background and they can be noticed from adjacent blocks. A powered ruin does not show as being lit from the street until the building is repaired.

Each block of a Large Building (Malls, Mansions, Stadiums, Power Stations and Cathedrals) can be ruined individually.

Junkyards and zoo enclosures can be neither ransacked nor ruined.

Repairing a Ruin

Repairing a ruined building requires that all zombies be removed and the survivor must have a toolbox in their inventory. It gives 1 XP and doesn't use up the toolbox. Repaired buildings have normal status (they are neither ruined nor ransacked).

As per the 28 May, 2008 update repairing ruin costs more AP the longer it has remained ruined. This seems to be equal to 1 AP per full 24 hours the building remains ruined, but as of yet, no cap has been established.
This AP can not be "split" - the option to repair the ruin is a single action that consumes multiple AP, just as standing up from a headshot (or without Lurching Gait) or manufacturing a syringe. This means that buildings untouched for a particularly long time can be impossible to repair.
Additionally, per the same update, if the building is dark the ruins must be lit by a fueled portable generator before repair efforts will succeed.

Ruin Effects

Ruining buildings prevents survivors:

• Barricading,
• Changing into new clothes
• Free running in (attempts land the survivor outside and may injure the survivor, though this injury never causes death)

Ruins (unless heavily or more barricaded, see pinata) can always be entered in the normal manner of entering a building. Free running out of a ruin into an intact building works as normal; the survivor moves to the interior of the neighboring intact building for 1 AP.

More information

• Decay