The only way to take an occupied building is by the bloody tactic of storming in with one of your units. This is called an assault. Each occupied building may be assaulted by a single unit during each Movement phase. The assaulting unit must declare a charge against the unit in the building. There can be no multiple assault charges against a building, as the assaulting unit is imagined to surround it. If multiple units are forced to declare a charge against an enemy-occupied building, only one can complete the charge – the controlling player decides which one will do so after rolling the charge distances. The other units automatically fail their charges.
An assault charge is resolved just as if the building were the target unit. If the unit's charge distance is equal to or greater than the distance to the building, it is successful, otherwise the charge is failed as normal. A unit that is assaulting the building is not allowed to charge another target at the same time – it must wheel to bring as many models as possible into contact with the building and close the door in such a manner that it does not contact any enemy units when the charge is completed.