FAIf non-current assets are improved e.g by $8000, do you add the value to the depreciable amount?

I don't know.

the answer is, yes you do

It all depends on whether the improvement is itself considered a separate depreciable asset or if it is an improvement on the current asset. For instance if a new wing is added to a building, that new wing may be recognised separately and depreciated separately. You have to look at the context.