Holes Near Your Foundation: Causes and When to Act

Holes right along a foundation usually come from chipmunks, Norway rats, or voles, all of which like the shelter a house wall provides — but water pouring from downspouts and settling backfill soil carve foundation-line holes too. Sorting burrow from washout matters, because a rat burrow against the house is the one that needs fast professional attention.

Most likely causes

  • Chipmunks — clean 2-inch holes with no soil, often under steps or foundation plantings
  • Norway rats — 2- to 3-inch worn holes with kicked-out dirt, sometimes angling under the slab
  • Voles — inch-wide openings with surface runways through mulch and ground cover
  • Downspout erosion — irregular washed-out cavities below or downhill from a gutter outlet
  • Settling backfill — soft dips and openings where the soil beside the foundation is compacting

Compare the possible causes

Possible cause Key signs When it happens How likely
Chipmunks Tidy, round 2-inch holes with no dirt pile, tucked beside steps, stoops, or shrubs against the house Spring through fall; new digging peaks in late summer Very common
Norway rats Holes 2 to 3 inches wide with fresh excavated soil, smooth well-traveled edges, and droppings or rub marks nearby Any time of year; burrowing accelerates in fall and around food sources like bird feeders and trash Common
Voles Openings about an inch wide connected by worn runways through mulch beds and ground cover along the wall Year-round; most obvious in early spring when winter runways are exposed Common
Downspout and drainage erosion Irregular, funnel-shaped cavities in the soil below gutters or where water sheets off the roofline, with no tunnel and no animal sign Appears or worsens after heavy rain, spring snowmelt, or gutter overflows Common
Settling backfill and old construction voids Soft depressions or small openings that slowly appear along the foundation line, sometimes swallowing mulch Gradual, but often revealed suddenly after a soaking rain Less common

Visual clues to check

  • Check for excavated soil: a dirt fan means rats or erosion deposit; a perfectly clean hole means chipmunk
  • Line the hole up with your gutters: a cavity directly under a downspout or roof valley is almost certainly water, not wildlife
  • Look for runways: narrow worn paths through mulch connecting small holes are a vole network
  • Inspect nearby walls at knee height and below for greasy rub marks, droppings, or gnawed corners — rat evidence
  • Probe gently with a stick: burrows angle away as a tunnel; settling holes and washouts are shapeless voids
  • Watch the hole for two mornings: fresh dirt, prints, or a pushed-out paper plug means an active animal

The causes in detail

Chipmunks

The strip of sheltered ground along a foundation is prime chipmunk real estate. Their burrows can run 20 to 30 feet, but a chipmunk tunnel is only about 2 inches across and rarely threatens a poured foundation. The realistic concerns are cosmetic sinking under walkway slabs and stoops after years of tunneling, and the fact that a clean rodent-sized hole near the house always deserves a second look to rule out rats.

Norway rats

Norway rats are ground burrowers, and the base of a foundation, slab, or stoop is one of their favorite den sites. Unlike chipmunks, rats leave dirt heaped at the entrance and wear the hole smooth with nightly traffic. The serious risk is proximity: a rat denning against your house will probe for gaps around pipes, vents, and sill plates, and a burrow can become an indoor infestation in weeks. This is the foundation hole that justifies calling a professional immediately.

Voles

Foundation beds mulched deep and planted with junipers or ivy are vole heaven — food, cover, and soft digging in one strip. Voles won't hurt the foundation, but they girdle the shrubs and perennials planted along it, chewing bark at the base under the cover of mulch. Small holes plus surface trails plus dying foundation shrubs is a vole pattern, not a structural one.

Downspout and drainage erosion

Concentrated roof water is powerful: a downspout without an extension can excavate a surprisingly deep hole and wash fines out of the backfill, leaving voids that later collapse into openings along the wall. Erosion holes are raggedy rather than round, have no worn tunnel leading away, and sit exactly where water lands. Left alone, this one actually can affect the foundation, by keeping soil saturated against it.

Settling backfill and old construction voids

The trench dug for a foundation is refilled with looser soil than the surrounding ground, and for years afterward that backfill compacts and settles. Buried stumps, form lumber, and construction debris rot and leave voids that open to the surface as neat little holes with no digger. Carpenter ants sometimes exploit the same rotting buried wood, so a stream of large black ants from a foundation-line hole is worth investigating.

When to worry

  • Any burrow with kicked-out soil plus droppings or gnaw marks — assume rats and act quickly
  • Holes or gaps that continue under the slab, stoop, or porch rather than stopping at the wall
  • Openings around utility penetrations, crawl space vents, or the sill line — potential entry points into the house
  • A depression along the foundation that keeps growing after rain, which signals ongoing washout or a collapsing void
  • Large black ants trailing in and out of a foundation-line hole, especially with sawdust-like debris

What to do now

  1. Walk the whole foundation and map every hole, noting soil, size, and distance from downspouts
  2. Fix the water first: add downspout extensions or splash blocks and regrade so soil slopes away from the house
  3. Remove rat attractants — seal trash cans, clean up birdseed and fallen fruit, and store pet food indoors
  4. For voles, pull mulch back to a thin layer, leave a gap at shrub stems, and clear dense ground cover in the beds
  5. Backfill confirmed-inactive holes with tamped soil, and bury quarter-inch hardware cloth where chipmunks repeatedly dig
  6. Seal gaps around pipes and vents with metal mesh and mortar — after any animals are gone, not before
  7. If rats are suspected, or holes align with entry points into the home, call a licensed pest control professional now rather than after you see one indoors

What not to do

  • Don't stuff burrows with poison bait where pets, kids, and wildlife can reach it
  • Don't seal exterior gaps while animals are still active — you can trap rodents inside your walls
  • Don't pour concrete into a hole before you know whether it's a burrow, a washout, or a settling void; each has a different fix
  • Don't flood foundation-line holes with a hose — you'll saturate the soil against your foundation and solve nothing
  • Don't dismiss a musty smell or scratching in walls near exterior burrows; that's the follow-up clue that matters most

Think you know the suspect?

These animals commonly cause this clue — see their full sign profiles:

Frequently asked questions

Can holes near the foundation damage the foundation itself?

Animal burrows rarely harm a poured or block foundation directly — the tunnels are small and shallow relative to the footing. The genuine structural threats are water-related: downspout erosion and washed-out backfill keep soil saturated against the wall and can undermine slabs, stoops, and walkways. Fix drainage problems regardless of what animal is or isn't present.

How do I tell a rat hole from a chipmunk hole by the house?

Soil and wear are the two tells. Chipmunks carry dirt away, leaving a clean 2-inch opening; rats bulldoze soil out into a fan at the entrance and polish the hole smooth with nightly use. Rat holes also come with corroborating evidence — capsule-shaped droppings, gnaw marks, and rub marks along the wall — that chipmunks don't leave.

Why do holes keep appearing under my downspout?

Each hard rain sends hundreds of gallons through that downspout onto one spot of soil, blasting out fines and carving a cavity. Adding a 4- to 6-foot extension or a splash block that carries water away from the wall stops the excavation, after which you can backfill, tamp, and re-mulch the area.

Is it safe to just seal the holes with steel wool or foam?

Only after you've confirmed nothing is living inside and nothing is entering the house. Sealing an active burrow traps or redirects the animal — sometimes into your crawl space. Do the paper-plug test for several days first, then close soil holes with tamped earth and close structural gaps with metal mesh and mortar; foam alone is chewed through easily.

Related yard clues

Yard Holes Two-Inch Holes in Yard: Chipmunk, Rat, or Something Else? A round hole about two inches across is classic burrow size, and the usual suspects are chipmunks, rats, and thirteen-lined ground squirrels. Chipmunk holes are clean with no soil pile, rat holes are worn and hug structures, and ground squirrel holes sit in open, sunny lawn — those three clues sort out most cases. Read the guide → Yard Holes Holes Under the Fence: What's Digging In (or Out)? A hole under a fence is usually a travel gap scraped out by rabbits, skunks, or a neighborhood dog — or the edge of a real burrow if a groundhog has moved in along the fence line. The key distinction is pass-through versus home: a shallow trench under the boards means something is commuting through your yard, while a deep hole with a big dirt pile means something is living there. Read the guide → Yard Holes Small Holes in Yard With No Mound: What's Digging? Small holes in your yard with no dirt mound are usually caused by squirrels, chipmunks, foraging birds, earthworms, or ground-nesting insects. The size of the hole, how deep it goes, the time of year, and whether the damage appeared overnight can narrow down the cause quickly. Read the guide → Yard Holes Large Holes in Yard: Groundhog, Fox, Skunk, or Armadillo? A hole 6 inches across or bigger is a den entrance, and in most American yards the owner is a groundhog — an 8- to 12-inch hole with a big dirt mound is their signature. Foxes, armadillos, and skunks dig or borrow similar burrows, especially under sheds, decks, and porches, so smell, mound size, and location are what separate them. Never fill a large hole until you know it's empty. Read the guide →

Still not sure? Compare with these clues

Home Exterior Clues Mud Tubes Near Your Foundation: The Termite Warning Sign Pencil-width mud tunnels running up your foundation wall are most likely shelter tubes built by subterranean termites — the single most important early warning sign of an active infestation. Mud dauber wasp nests and rain-splashed soil can look similar at a glance, but termite tubes follow continuous vertical paths from soil to wood. Of every clue on this site, this is the one that should never wait: schedule a licensed termite inspection promptly. Read the guide → Yard Holes One-Inch Holes in Lawn: Identify the Digger by Size Holes about an inch wide in a lawn are most often the work of voles, young chipmunks, ground-nesting bees, or — in wet, low-lying yards — crayfish. An inch is a telling size: it's too big for most insects and too small for rats or full chipmunk burrows, so checking depth, soil, and location will usually name the digger. Read the guide → Animal Droppings Droppings in the Garage: Mouse, Rat, Bat, or Squirrel? Droppings in a garage are most often from mice, with rats, bats, and squirrels as the other usual suspects. Mouse droppings are 1/4-inch pellets with pointed ends scattered along walls and shelves; rat droppings are two to three times larger with blunt ends; bat droppings pile up in one spot beneath a roost near the ceiling or wall top. Before you identify anything, know the cleanup rule: never sweep or vacuum rodent droppings dry. Read the guide →