The attic in my 1896 house was finished by a previous owner. I recently found out that the floor is, I believe 3/8" plywood. Is this thick enough? If not, how thick should it be? Should I pull up what is there an replace it with the required thickness, or is it okay to add more plywood on top of the existing plywood?

I also think the seams are not on joists, there are spots where the plywood feels off. The floor is carpeted, so I am not 100% sure.

Thanks,

Ron