Breaking down scene to modular pieces Can i build my entire model within the same scene, then export each piece individually so that they're modular in UE4?

Or do i have to build each piece within its own scene and export separately.

For example

i made 10x1x10 wall and then duplicated it and used the same dimensions with a door cutout in the second piece and then selected the first mesh to export into UE. 

But when i went into UE4 both pieces were there meaning Blender exported everything in the scene. 

So how do i just export the pieces i want one by one after building the entire model?.
Each object can be exported as a separate FBX file. Just select one and check the Selected Objects in the export settings.