Navigation - Avoid Initiated Buildings

Hello,

I'm working with the built in navigation system in Unity. So far, it works fine, its avoiding the scenery well. But my game is kind of based around a RTS, so whenever I place a building during run time, the building isn't baked within the Navigation system, so it gets ignored by the agents (thus resulting in them just walking straight through it).

Any ideas how I can add the building to the bake during run time?

Thanks