After exclusion, I sprayed some foam sealant in cracks I couldn’t reach easily, then layered steel wool over it. That combo held up well against gnawing.
Use a UV flashlight or blacklight, droppings and urine glow under UV. Helps you find where to place traps or bait.
Once I caught a few, I cleaned up all their nesting debris, paper, insulation fluff, etc. Removing that hides their scent and discourages reinfestation.
@NoiselessNina Good point. Traps alone aren’t enough. Combine sealing, trapping, and upkeep checks for a few weeks. That’s how you win.
I treat the attic first, then move to walls, floors, and lower levels of the house. Rats like to shift downwards if attic gets active. Be methodical.