Problem with camera focaldistance? Static mesh not participating in DOF.

Hi, I’ve been experimenting with UE4 as an archi viz tool and so far so good, however in one of my test scenes I can’t get the dof effect to work properly on the static mesh that is outside my room. This is what the scene looks like with a slight dof effect enabled on the far side of the room. The mesh outside the room just won’t participate in the effect no matter what I set as focal distance.

So, I enabled Visualize > Depth of Field Layers and it shows that the mesh outside the window as a different layer judging by its shade of grey but I can’t get it to appear out of focus :frowning:

What am I doing wrong guys? Any suggestions on how to fix it?

EDIT : No matter what I change or set in the Depth Of Field properties of my camera, that space outside the window stays grey.