The most reliable sign of rats under decking is the presence of burrow entrances, roughly 3 inches in diameter, with smooth, compacted edges and no cobwebs or debris blocking the opening. An active burrow looks well-traveled and clean, while an abandoned one collects dust and spider webs. But burrows are just one piece of the puzzle. Rats leave several other telltale clues that, taken together, confirm you’re dealing with a rodent problem rather than another animal.
Burrow Entrances and Soil Disturbance
Rats are subterranean animals, and the sheltered, dark space beneath a deck is prime real estate. Look around the perimeter of your decking, especially where the deck meets a wall, fence, or shed. Active burrow holes are about 3 inches across and appear smooth around the edges from repeated use. The soil directly around the entrance is often packed down and free of leaves or grass clippings.
What makes rat burrows particularly concerning under decking is depth. Rats can burrow straight down at least 36 inches into the ground, which means they aren’t just scratching out a shallow den. Over time, extensive burrowing can undermine the soil supporting your deck’s footings or posts. If you notice soil sinking or shifting near structural supports, rats may have hollowed out the ground beneath them.
Droppings Along Travel Routes
Rat droppings are one of the easiest signs to spot and identify. Norway rats (the common brown rat found in most yards) leave rectangular pellets about 3/4 inch long with blunt ends, usually clustered in small groups. Roof rats leave slightly smaller droppings, around 1/2 inch long, that are curved with pointed ends and more scattered.
Freshness tells you a lot. Fresh droppings look dark, shiny, and moist. After a few days they dry out and turn gray and crumbly. If you’re finding fresh droppings near your deck’s edges, along fence lines, or on nearby paths, the infestation is active. Check where the deck boards meet the house wall, around any gaps in the skirting, and near stored items like garden furniture or firewood.
One common source of confusion: squirrel droppings are similar in size to rat droppings but have a noticeable twist or pinch at the midpoint. Mouse droppings are much smaller, only about 1/4 inch long, roughly the size of an uncooked grain of rice with pointed ends.
Gnaw Marks and Material Damage
Rats gnaw constantly to keep their continuously growing front teeth in check. They can chew through wood, plastic, rubber, vinyl, aluminum sheeting, and even concrete block. On a deck, look for fresh gnaw marks on joists, support posts, lattice skirting, or any plastic or rubber components. Fresh gnaw marks are lighter in color than the surrounding material and have visible parallel grooves from the teeth.
Electrical wiring and outdoor lighting cables running near or under the deck are also at risk. Rats frequently gnaw around pipes, conduits, and cables. If outdoor lights or electrical outlets near your deck stop working, damaged wiring is a real possibility, and a potential fire hazard. Any small gap or crevice in your deck’s structure can be quickly enlarged by gnawing, turning a minor opening into a rat-sized entrance.
Sounds, Smells, and Nighttime Activity
Rats are primarily nocturnal. If you hear fast scurrying or scratching sounds from beneath your deck after dark, that’s a strong indicator. The sound is distinctly rapid and light compared to the heavier, slower movement of raccoons or opossums. Raccoons also produce chittering and scratching noises, but they’re louder and more deliberate.
Smell is another giveaway. Rat urine has a sharp, ammonia-like odor that intensifies in enclosed spaces. If you notice a persistent, unpleasant smell near the base of your deck, especially in warm weather, an active colony is likely. Rats also build nests from shredded material like insulation, leaves, fabric, or cardboard. Finding piles of shredded material near or under the deck confirms nesting activity.
Greasy Rub Marks and Worn Paths
Rats follow the same routes repeatedly, running along walls, fence lines, and structural edges. Over time their oily fur leaves dark, greasy smudge marks on surfaces they brush against. Check the bottom edges of your deck skirting, nearby fence panels, and the base of walls adjacent to the deck. These rub marks are subtle at first but become more obvious as traffic increases. You may also see worn, narrow trails through grass or mulch leading to and from burrow entrances.
Ruling Out Other Animals
Several animals shelter under decks, and correctly identifying which one you’re dealing with saves time and money. Raccoons leave much larger droppings, show signs of digging for grubs, and produce louder nighttime noises including distinctive chittering. Opossums are quieter, nocturnal, and generally don’t create burrows. Squirrels are mostly active during the day, so daytime scurrying overhead or under the deck points to squirrels rather than rats.
The combination of small (3/4 inch or less) pellet-shaped droppings, 3-inch burrow holes, gnaw marks, and fast nighttime scurrying is unique to rats. If you’re seeing all of these signs together, you can be confident about the identification.
Health Risks of Rat Activity
Rat droppings, urine, and saliva carry serious pathogens. Diseases spread through direct contact with contaminated material, through breathing in particles from dried waste, or through contaminated food and water. The bacterial infections most associated with rats include leptospirosis (spread through urine-contaminated water or soil), salmonellosis, and rat-bite fever. Hantavirus, though more commonly linked to certain mouse species, is also a concern with rodent waste in enclosed or semi-enclosed spaces.
If children or pets play near the deck, the risk increases. Avoid sweeping or vacuuming droppings dry, as this can send contaminated particles airborne. Wet the area first and wear gloves during cleanup.
Trapping and Removal
Snap traps remain one of the most effective tools for dealing with rats under decking. Place traps along the edges of walls, fences, or deck skirting where rats naturally travel, with the trigger facing the wall or structure. Use multiple traps rather than relying on a single one, and set them in pairs or groups of three.
For bait, choose something the rats are already eating nearby, or use a pea-sized amount of a food attractant like nut butter placed on the trigger. A useful technique called prebaiting involves placing baited but unset traps for a couple of days until the rats are comfortable eating from them, then setting the traps once the bait has been taken multiple times. This dramatically increases catch rates.
Always wear gloves when handling traps or removing caught rodents. Double-bag any carcasses before disposal, and check local waste regulations since some municipalities don’t allow rodent carcasses in regular trash. Stake or tie down traps to reduce the risk of catching non-target animals like birds or raccoons.
Preventing Rats From Returning
The space under a deck is attractive to rats because it’s sheltered, dark, and often undisturbed. Physical exclusion is the most durable solution. Hardware cloth (galvanized wire mesh) with openings no larger than 1/2 inch can be installed around the deck perimeter to block access. Because rats can burrow 36 inches straight down, the mesh should extend below ground level, ideally buried in a trench at least 12 to 18 inches deep with an L-shaped footer angled outward to discourage digging underneath.
Eliminate food sources nearby: secure trash cans, pick up fallen fruit, remove bird feeders or switch to designs that don’t scatter seed on the ground, and don’t leave pet food outside overnight. Keep vegetation trimmed back from the deck’s edges, since rats use dense plantings and overgrown shrubs as cover. Store firewood, garden supplies, and other clutter away from the deck to reduce hiding spots. Rats are opportunistic, and a deck that offers food, shelter, and concealment is far more vulnerable than one that doesn’t.