Kallast vs kallaste. I've never fully understood when to add the 'e' - it seems inconsistent. Is it a bestämd vs obestämd thing?
Yes, just as you say ett kallt rum but det kalla rummet with an -a you add an -e to the superlative: Rummet är kallast but det kallaste rummet.
Is there anywhere this system is explained in detail? I'm finding it quite confusing.
Cheers, thanks for clarifying!
I would say "Jag bor i kallaste rummet." Why is Det necessary?
It's not grammatical to leave it out, though some people may do so in colloquial speech.
Im swedish and i didnt even know it was supposed to be det kallaste i kormally just say jag bir i kallaste rummet