Converting to Static Mesh problem

So I created part of my map for my game quite early in a somewhat inefficient way, but I should still be able to convert parts of it to a static mesh to tidy it up for the sake of performance. However when I try to convert these older pieces of my map to a static mesh I the parts basically become hollow and I haven’t really been able to find anyone else with this problem anywhere. Btw I’ve tried copying and pasting the part, alt dragging it, and reapplying the textures, same result each time. alt text

could be some bad normals. before converting to static mesh what does it look like from the back side? is there geometry there

How would I go about trying to fix normals in case that is the problem?

based on your picture id say its not a normals issue. looking back at the previous pictures, the third one in particular, it looks like that plane of geometry is out of place like its visible through the windows. im not sure what would cause an issue like that.