Jack,
I avoid using SEO operations with the mesh as much as possible.
If the foot print of your building is not too complicated, Create a Hole in the mesh instead of using multiple SEO's operations.
Win 10 Home Premium - AMD Phenom IIX6 1090T Processor 3.20 GHZ 8.00 GB RAM 64-bit Opp. Sys NVIDIA Quadro 4000 AC 22, MEP