I actually have a separate mesh to add where the window holes are that are recessed as you said and consists of the frame and glass. I fill them in after it is all imported to UE4. I am going to do some tests myself and check out render time, memory usage and fps with a couple different options. I am still learning the best techniques to used for mesh building… I am old school and would rather build everything out of bsp’s but even after you convert them to a static mesh you have to create a valuable lightmap for them because they don’t look good by default. I mapped with hammer editor with the source engine for years and it was much faster to build levels. I wish the bsp’s would get optimized better. As soon as you map downloads I will take a look.