> Roller shutters, nothing easier than that. These things are standard in Germany.
The problem is not that they can't figure out how to cover the window, the problem is that you're forcing them to pay extra for the window they're only going to cover up.
> The problem is slumlords.
Slumlords exist because housing supply is constrained. If good housing was affordable, nobody would take a trivial discount to live in a slum.
> Allowing usage of unfit rooms (i.e. no/small windows, basement rooms) for permanent living once makes it very hard to force landlords to upgrade these rooms or condemn them later on
The key is to force them through competition rather than zoning. Nobody wants to live in a crappy apartment but they will if it's the only thing available to them. Make something better affordable and the owner of the crappy apartment would have to improve it to find a tenant.
> Rooms without windows to escape are deadly fire traps, and basement rooms can be just as deadly (or at least destructive) in floods.
Rooms don't have to have windows to have fire exits. "Floods can destroy your stuff" hasn't prevented every suburban homeowner from keeping stuff in their basement, and it's not obvious how that's even relevant to residential tenants keeping their stuff in the interior section of an above-ground floor of a formerly commercial building.
> Whatever we create now will most likely outlive us, so we better do it right now instead of just kicking the can down the road for the next decades!
Buildings last a long time. What you use them for can change in a week. If you turn a commercial building into low-cost apartments during a housing shortage and then you later resolve the housing shortage by building higher quality apartments, you can turn it back into a commercial building, or whatever else is needed at the time.
The problem is when you're prohibited from converting it to the use which is currently in demand, and then rents are high and people are screwed because you took away a bad option and only left a worse one.