Attic Space

Is there a minimum size on attic space before it needs access?

If 30 inches of unobstructive headroom can be provided and if the building has compustible ceiling or roof construction.

As stated…

Attic accesses are required for any attic that has a clear ceiling height of 30 inches or more, and the opening needs to be a minimum of 22 inches by 30 inches in size.

Note that one dimension is 22 inches instead of 24 inches - the building codes have made this adjustment so that access holes will fit between commonly used roof trusses, which are usually on 24-inch centers.
Here again, the codes don’t typically specify inside or outside access.