A live oak canopy over a residential street in New Orleans where roof rats travel

Step 1: work out which rat you have

This decides everything else. Roof rats are slim and dark with a tail longer than their head and body combined, and they live high: attics, soffits, upper walls, tree canopy. Norway rats are heavier, browner and blunt-nosed, and they live low: pier spaces, burrows along the foundation, storm drains and catch basins.

If you cannot see one, read the droppings. Roof rat droppings run about half an inch and taper to a point at both ends. Norway rat droppings are larger, up to three quarters of an inch, and blunt like a capsule. Mouse droppings are about the size of a grain of rice. Fresh droppings are dark and soft, old ones are gray and crumble.

Location tells you nearly as much. Noise overhead after dark is a roof rat. Noise under the floor of a raised house is a Norway rat. Rustling in a kitchen cabinet at night is usually a mouse.

Step 2: find how they are getting in

Walk the outside of the building and look up. Soffit and fascia joints, gable and turbine vents, the junction where a lower roof meets a wall, and anything touching the roof: live oak limbs, palm fronds, banana clumps, cable lines, a fence running to the eave.

Then look down. If the house is raised, get under it or at least look along the skirting for missing boards, open pier bays and burrow holes at the perimeter. On a slab house, check weep holes, the space behind brick veneer at grade, AC line penetrations, dryer vents and the bottom corners of the garage door.

Then inside. Under the kitchen sink and behind the dishwasher, around the tub trap, in the water heater closet, and anywhere a pipe passes through the floor. Use the quarter test: if a gap is as wide as a quarter, a roof rat can use it. A dime-sized gap is enough for a mouse.

Step 3: trap, and put the traps in the right place

Placement decides the outcome. Rats travel with a wall or a beam against their flank and avoid open floor, so traps go tight against the wall, along rafters and top plates, on joists under the house, and behind appliances, with the trigger toward the wall. Set several. One trap on a runway with an established population is not going to keep up.

Bait matters far less than people think. Peanut butter, dried fruit or a wad of cotton all work. Expect the first catch to take a few nights, because rats are wary of new objects in a space they know.

Skip glue boards for rats. They usually will not hold a full-grown rat, and one that drags a board into a wall void creates a worse problem than you started with.

Step 4: seal the building, or you will do this again

This is the step homeowners skip and the reason rats come back. New Orleans has no freeze hard enough to cut the outdoor population, so the pressure on your house is constant and year round. An unsealed house gets found again within a season.

Use materials rats cannot chew. Galvanized hardware cloth over vents, open pier bays and skirting gaps. Sheet metal or flashing at soffit and fascia joints. Copper mesh packed into pipe penetrations and then sealed over. Expanding foam on its own is not exclusion. Neither is caulk on its own. Rats chew both.

Then cut the access: limbs back from the roof, vines and ivy off the walls, firewood and stored material away from the foundation.

Step 5: clean up what they left

Droppings, urine and nesting material carry bacteria and, just as importantly, carry scent that tells the next rat the space is good. In an attic that usually means removing contaminated insulation rather than trying to save it.

Do not sweep or vacuum dry droppings with a household vacuum. That puts the dust in the air, which is exactly what you do not want to breathe. Protective equipment and a HEPA-filtered vacuum are the right tools.

When to stop doing it yourself

Call someone if you are hearing activity in more than one part of the house, if you have been trapping for two weeks and the catch is not slowing, if the rats are in the attic or under the floor where you cannot easily work, or if you have found chewed electrical wiring. Chewed wiring in an attic is a fire risk and not worth waiting on. Call 504-395-3296 and an experienced local exterminator can take it from the inspection.

How to Get Rid of Rats in New Orleans