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