CGT on renovated PPOR?

Is there a limit on the amount of money one is allowed to invest in renovating your PPOR before it loses its CGT exemption?

I think I read it somewhere a few months ago but am at a loss to recall where, but an amount like $170K comes to mind.

I want to very substantially my PPOR in a couple of years, and while not ever intending to sell it, do need to keep open the possibility that I might one day change my mind.

Can anyone offer enlightenment on this?
I don't think there is ANY limit, as long as it is your PPOR and you are not making a business of doing it year after year.