I have been playing around for ages and cannot do it! I even made something in Blender but it only imports as an actor not a brush so I cannot cut holes in objects with ‘subtractive’.
Any help is appreciated, I can’t seem to find anything on YouTube either re round or curved windows in UE4.
Yes and no ^^ -> you can create simple curved stuff, but there is no way to smooth them! When you want something curved, just add more vertices and place them so that you get a curved shape.
So for a “real” curved shape you will have to use meshes from a 3d program
That’s great thanks, can you just explain how I can add vertices to existing brushes please? I have been trying but failing, I cant seem to find the option and its frustrating 
Go into the brush editor - select an edge of the brush - click on split
But dont expect too much (better when you do it in a 3d program) ^^
Thank you very much indeed :O)
If you don’t mind can I just ask, I created an arched window in Blend and exported it as an FBX file. Its in UE4 but I cannot cut that shape hole out of the wall in UE4 because its obviously not a brush. Is there a way I can change its type in Blend and import it as some kind of cutting tool? Is that the mesh you were referring to? Sorry this is all very new to me
No, it’s not possible to convert a mesh to a bsp brush. So when you use meshes you will have to edit them in your 3d program - import them.
Ok cool so when its imported as a mesh into UE4 I can then use it to cutout holes in UE4 objects? Is there a special file type or just FBX? Sorry ill spam you with questions because this has been an all-dayer trying to sort it out and its really annoying lol
Oh wait - I re-read it sorry…so I cannot cut into UE4 objects with anything imported, I have to import the walls etc too then? Ahh I think I see now thanks
You could use a combination between meshes and bsp brushes, but it’s recommended to just use meshes in your levels -> performance + more flexibility (uv mapping, advanced shapes,…)
Just for clarification
bsp brush -> an inbuilt geometry editor in the UE4 (should be used for prototyping and not for entire levels)
meshes -> 3d objects which were made in a 3d program like blender/3ds /maya. They cant be modified in the engine (you can just add materials and collisions to them)
Thanks for all your help you have been very patient and helpful today cheers
What I like to do, just for blocking out purposes, is to create a doorway sized subtractive brush, and place a cylinder of matching dimensions on top of it, and align it so the center of the cylinder is right on top of the doorway. Make sure they are both subtractive, and you should be able to cut out perfect arches