Your best bet might be to extend the duct a few feet above the roofline to make the vent inaccessible to rats.
Roof vents and rats.
Caulk all exterior wall cracks.
Chris cudmore oct 24 13 at 18 29.
One common style of vent that is located on the roof is commonly called a j vent.
Rats can easily climb pipes rain spouts cables and other vertical objects where holes can provide an entrance to your home.
The soil vents also known as a vent stack can let rats into your home.
I actually don t think this can be done legally.
Rats climb down and get into your plumbing system and get into your home through the toilet.
Rats often enter homes and business s through vents located on the roof.
These entry points need to be sealed in order to prevent rats from entering the structure through roof vents.
Use a heavy grade of steel wool copper mesh or metal scouring pads to fill cracks and holes in exterior walls.