In Houdini, my asset is made of multiple parts and then I merge them all at the bottom of the graph into my output.

When I bring my asset into unreal, there is only one mesh with multiple material slots. I assume that's why I get overlapping lightmap uv errors when I try to bake the lighting, let me know if I am wrong.

I figure that by using the rendered_collision_geo prefix I could split my mesh into pieces (rendered_collision_geo_walls, rendered_collision_geo_floors, etc.) but this just brings in multiple copies of my entire mesh.

Any help is appreciated.

Couple of things could be wrong depending on how you are doing the UV's in Houdini.

Ideally, you want UE4 making your lightmaps. It has a really good layout algorithm and you get really good results bar some very fringe edge cases. Infact, in my opinion this is one of the strengths of UE4 over other engines.

To get this going there are a few prerequisites. 1. UE4 currently only uses existing islands for packing its light maps. This means you need to have nicely laid out UV's for each of those multiple parts. There should be no issues having multiple overlapping UV's with different materials if thats what you are going for because Unreal will pack them with proper padding during this process. However, the islands have to be legit.

2. Ensure that Unreal is calculating lightmaps. I know how to do this through a generic mesh import, but not through Houdini sorry. It should happen automatically because it is a default setting however.

3. When you edit your mesh, ensure it is using the correct UV channel for the lightmap. If you have only laid out your UV's in 1 channel, then this should be UV index 1 (since it starts with 0)

Hopefully this helps