One way to avoid silos is to assign leadership roles to needs-based teams. Such teams only exist until the needs are met and work from agreed goals to contribute to school improvement. This approach helps maintain high morale. The following link leads to an overview of distributed leadership.
A one-team approach
The school leader needs to be in control of culture and proactive in ensuring a 'one team' approach. Silos of power should not exist. These are self-serving groups within a school that develop subcultures, becoming exclusive and competitive. They are counter-productive and a hindrance to building a school-wide culture.
Image courtesy of Michael Leunig