I have a problem with join meshes. In grasshopper I’m using the Pufferfish Offset Mesh component to give thickness to different joined meshes. The geometry seems to work in gh
Joining meshes to large complicated objects always brings some challenges further down the line. Use Mesh Flip after UnifyNormals to reverse the direction. If in doubt, simply bake the mesh to Rhino and use Dir command to see the directions.