Attic Space

[lmills]

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

[rnewman1]

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

[David P. Valley]

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.