Is there a consistent rule when you double the n's ?
This has to with how these words are derived
innovation = in + novation
1540-50; < Latin innovātus past participle of innovāre to renew, alter, equivalent to in- in-2 + novātus (novā(re) to renew, verbal derivative of novus new + -tus past participle suffix)
renovation = re + novation
1400-50; late Middle English (adj.) < Latin renovātus (past participle of renovāre), equivalent to re- re- + nov(us) new + -ātus -ate1
so innovation has two n's because the prefix and root both have n