#5 Vent blockage
There is a chance that birds will build a nest in your roof vents if they go over the gutters but ignore the chimney. They will break open the mesh and build their nest there, which can cause a few issues. Not only is it possible for them to possibly access your attic through the vent (and we discussed the problem that creates earlier), but they will also block the airflow and damage the vent.
The blockage will also mean your vent system is not running correctly, and this can lead to moisture build-up on the upper floors, which in turn can be the cause of rotting in the support beams and even cause mold to grow inside your walls.
They are cute, but giving them an alternative space to nest would be better than leaving them there.
