Strange behavior with dxf 3d data in Blender

Hey there,

i’m working alot for architectual visualizations in blender and i get allways this problem with 3d dxf data in cycles. When i render the data with cycles in blender, there showing some wierd lines up and most faces looking shredered (First Image). GPU and CPU both. In Viewport, the mesh looks good. I haven’t these problems when i render it with BI. (Second Image)

Allready tried to “remove doubles”, recalc normals. I really dont know whats the problem is.

Maybe you got an idea.
Thanks for watching