Rats are larger, warier and harder to trap than mice, and they follow different routes — along fence lines, through sewers and drains, and into basements and ground-floor rooms. Keeping rats out is a different job from keeping mice out, and the plan fits the rat: larger gaps, different traps, and the sewer and drain routes that mice never use.
The work has three parts, in order: seal the gaps rats use, remove the food drawing them to the wall, and trap on the routes rats actually travel. Sealing is the half that lasts. Trapping without sealing is a subscription to the same problem.
TL;DR
Problem: rats using sewers, drains, and fence lines to reach the house.
Solution: seal the larger gaps, remove the food at the wall, and trap on the rat routes.
When to call: at the first sign — large droppings, gnaw marks on wood, or rats seen in the yard.
How rats get in
Rats enter through larger gaps than mice — a gap the width of a thumb, a broken drain cover, a vent that has lifted, a gap at the roofline where a tree touches the house. Roof rats use trees and vines to reach the roofline and enter through gaps at the eaves. Norway rats use sewers and drains to reach basements and ground-floor rooms. The inspection maps the gaps by size and by route, because the sealing differs for each.
The routes rats use
Rats travel along fence lines, through sewers and drains, and along the wall lines of basements and ground floors. They avoid open space, and they follow the same routes night after night. Traps placed on those routes catch rats; traps in the middle of a room catch dust. The inspection's map of droppings and rub marks is what puts the traps in the right places.
Food at the wall
A bird feeder spilling seed by the foundation draws rats to the wall every evening. A compost pile against the house feeds them. Pet food left out overnight feeds them. Garbage bins with loose lids feed them. The food list is worked through alongside the sealing, because a house with food at the wall will always have rats at the gaps.
Sealing for rats
Rat sealing uses materials rats cannot chew through — metal mesh, cement, hardware cloth — and it covers the larger gaps mice never need: the broken drain cover, the lifted vent, the roofline gap where the tree touches the house. The tree limbs touching the roof are cut back, because roof rats use them as a bridge. The sealing is done as the trapping clears the population inside, so new rats cannot replace the ones removed.
Steps
Look for the larger signs
Large droppings, gnaw marks on wood, rub marks along fence lines and wall lines, rats seen in the yard at dusk.
Map the routes
Follow the signs to the gaps — the drain, the vent, the roofline, the fence line — and list every one.
Seal with chew-proof materials
Use metal mesh, cement, and hardware cloth. Cut back tree limbs touching the roof.
Trap on the rat routes
Place traps along the fence lines, the wall lines, and the basement runs where the signs are thickest. Check over weeks.