Commercial tenant on first floor - does this include basement?

[Peter Fokas]

Recently acquired a property that has 1 commercial tenant (restaurant). They are on first floor of building and have been using the basement for storage and other things.  Their written lease with the seller does NOT state anything about use or access to basement. It only states 1st floor.  The seller did let them use the basement (I guess verbal agreement). I on the other hand want everything in writing so can I tell this commercial tenant that they cannot use the basement based on the written lease. I am amenable to allowing them to use the basement but not for free and in writing. Can I do that? Is there any "unwritten" rule that when renting the first floor of a building it automatically includes basement?