Use a heavy grade of steel wool copper mesh or metal scouring pads to fill cracks and holes in exterior walls.
Roof vents and rats.
The soil vents also known as a vent stack can let rats into your home.
If you have overhanging trees textured walls or anything that would let a rat climb on your roof then you should have aluminum screens installed on all your soil vents.
Rats often enter homes and business s through vents located on the roof.
Rats can easily climb pipes rain spouts cables and other vertical objects where holes can provide an entrance to your home.
Especially on a roof where you will have difficulty getting up to clean it.
On your roof seal off openings such as vent pipes.
One common style of vent that is located on the roof is commonly called a j vent.
Chris cudmore oct 24 13 at 18 29.
Your best bet might be to extend the duct a few feet above the roofline to make the vent inaccessible to rats.
Rats climb down and get into your plumbing system and get into your home through the toilet.