Hello, Mr Raynor. I actually called an appraiser today that I have known for years to verify what I thought I knew, before i answered your question. I wanted to check from the authority for you. He concurred that a basement, finished or not , is not included in the square footage of the home. Below ground level is not part of the square footage. In reality, most basements were never constructed to be finished. They were only meant to hold up the rest of the house . This is especially true in Drexel Hill, where my team and I do much of our business. Even a walk out basement, where there are no windows on the other three walls, or the windows are below ground should not be included. In new construction, many homes are now built at grade and the walk out in level with the yard space. Then the measurements could be included. I hope this helps. Please email me at email@example.com or call me at 610-574-6203 if you wish to discuss this further. Thanks for the great question!