How to reduce squalor?

Any buildings that I can build? I can't upgrade the city/fort yet.
Thanks for any replies.

I think buildings that give a health bonus reduce the growth of squalor. Even if they don't, their health bonus counters its affects anyway.

So the buildings you need would be the Town Hall line of buildings, Bimaristans as Muslim teams, Public Baths and Aqueducts as Byzantium. Also high level religious buildings give a health bonus.

also make sure that the city is not overpopulated. If you have a wooden wall around a city with a population of 20,000 then that will definately be an issue

Alright, thanks. And if the city is overpopulated, I take it there's nothing for it but to let them starve until I can upgrade the city?

If you can upgrade it yet because there's not an option, then the city/castle isn't over populated.

There are some traits that change squalor and no buildings, but overall it is determined by the % population of the maximum the current walls can hold, up to 80%.