Small Holes Around Foundation of House: Causes & Fixes: Fast-Track Guide to Identifying and Solving Foundation Hole Problems

Noticing small holes around the base of your house usually means something is tunneling, seeking food, or exploiting drainage paths. Left alone, these voids can invite moisture, undermine soil bearing capacity, and create pest highways into your crawlspace or basement. The U.S. Environmental Protection Agency notes that moisture intrusion is a primary driver for pest activity in and around foundations, while industry data show that even a 1/8-inch gap can admit mice. Workplace and building research echoes the impact of poor environmental control: according to Steelcase research, environmental discomfort and distraction can cut task performance by double digits—at home this translates to maintenance oversights that compound small defects into costly failures. Add to that WELL v2 guidance highlighting moisture and pest prevention as a health safeguard, and the case for early action is clear.

From a structural standpoint, voids along a foundation can concentrate water, soften soils (reducing bearing capacity), and accelerate freeze–thaw damage. The Illuminating Engineering Society’s guidance on exterior lighting underscores safe, glare-controlled inspection lighting outdoors—a practical reminder that you’ll find and fix more when you can properly see grade transitions and weep paths after dusk. To ground this in numbers, Steelcase’s research on environmental quality links improved monitoring and upkeep with higher perceived control and reduced stress—conditions that, in residential settings, correlate with proactive home care. Additionally, WELL v2 Moisture Management strategies emphasize exterior drainage and pest-proofing as first-line defenses for occupant health and building durability.

Common Causes of Small Holes Near Foundations

I typically see six recurring culprits, each with a distinct hole size, soil signature, and risk profile:

1) Rodents and Small Mammals

- Mice and Rats: Entry points as small as 1/4 inch for mice and 1/2 inch for rats. Holes may appear under siding laps, meter penetrations, or at slab edges. Fresh rub marks or droppings are telltales. Steel wool stuffed into voids is only a temporary deterrent; you need rigid metal mesh and sealing compounds.

- Voles: Golf-ball-sized openings in mulched beds, shallow runways through grass, and sudden plant decline. They rarely breach the foundation but undermine landscaping and can expose the footing to surface water.

- Chipmunks: 1–2 inch holes, little to no soil mound, often at downspout ends, steps, and patio edges. They like warmth near foundations and will follow utility lines.

2) Insects

- Carpenter Ants: Often use existing gaps; look for frass (sawdust-like) near siding bases. Moist wood is an attractant—fix drainage first.

- Ground-Nesting Bees/Wasps: Clean round holes in dry, sandy soil. These are seasonal; filling with damp soil and improving ground cover usually resolves.

3) Burrowing Wildlife

- Moles: Volcano-like mounds and sub-surface tunnels; they chase grubs and aerate soil. Structural risk is low but can redirect water toward the foundation.

- Groundhogs/Skunks: 4–6 inch entries with significant spoils, often under decks and steps. These can undercut stoops and porch slabs.

4) Water and Erosion Pathways

Poor downspout discharge and negative grading carve channels. Repeated saturation reduces soil density; frost heave then opens voids at the foundation–soil interface.

5) Construction Voids and Settling

Backfill settlement after utility work or new landscaping can leave sinkholes along the foundation line, especially with overwatered beds or heavy irrigation.

Quick Diagnostics You Can Do in 30 Minutes

- Measure: Note hole diameter and count. Photograph with a coin for scale.

- Inspect Soil: Fresh, damp, or pellet-like spoil suggests mammals; clean, sand-only bores hint at solitary bees.

- Track Activity: Smooth the area in the evening; check for fresh disturbance in the morning.

- Moisture Check: After a rain, look for ponding against the foundation and flow from downspouts.

- Entry Scan: Walk the perimeter at dusk with a soft, glare-controlled flashlight to spot gaps at sill plates, vents, and penetrations.

Targeted Fixes by Cause

Rodents and Chipmunks

- Exclusion: Install 1/4-inch galvanized hardware cloth as an L-shaped barrier—12 inches down and 6–12 inches out from the foundation, backfilled with compacted soil and gravel. Seal utility penetrations with a backer rod and elastomeric sealant, then cap with metal mesh.

- Trapping/Control: Use covered, tamper-resistant stations positioned along runways. Avoid broadcast poisons that can lead to secondary wildlife harm.

- Habitat Adjustments: Replace dense groundcovers against the foundation with river rock or open mulch; keep firewood and storage 20 feet away.

Voles and Moles

- Turf Strategy: Reduce grub populations via targeted biological controls (e.g., beneficial nematodes) to remove the food source for moles.

- Bed Edges: Use steel edging or buried mesh skirts around ornamental beds near the house to discourage tunneling toward the foundation.

Groundhogs/Skunks

- Structural Protection: For decks and stoops, add a buried apron of welded wire mesh (2x4 inch) 18 inches deep and 12 inches out. Skirt the perimeter with ventilated, chew-resistant panels.

- Humane Removal: Coordinate with local wildlife control where relocation is regulated.

Ground-Nesting Bees/Wasps

- Soil Management: Lightly moisten and tamp, then overseed with deep-root turf or groundcover. Avoid pesticides when possible; pollinators are beneficial.

Carpenter Ants

- Moisture First: Correct leaks, splashback, and mulch piled against siding. Replace damaged trim and ensure a minimum 6–8 inches of visible foundation above grade.

Moisture and Drainage Corrections (High-Impact)

- Downspouts: Extend leaders 6–10 feet from the foundation. Use hinged extensions to maintain access while directing water away.

- Grading: Aim for at least a 5% slope (6 inches drop over the first 10 feet). Where space is tight, consider a shallow swale or a strip drain.

- Surface Materials: Replace fine mulches that float and migrate with angular gravel that locks in place and discourages burrowing.

- Splash Control: Add kickout flashing where roofs meet walls to prevent water streaking the foundation line.

Sealing Small Gaps and Penetrations

- Sequence: Clean, dry, backer rod for depth control, elastomeric or polyurethane sealant, then protective mesh cap where gnawing is a risk.

- Vents: Use louvered, screened covers rated for pest exclusion; maintain free area for required ventilation.

When Layout and Landscaping Help

Good exterior organization reduces habitat and water traps. If you’re reworking planting beds, edging, or patio lines adjacent to the house, prototype the geometry and drainage zones first with a room layout tool so your hardscape grades, planters, and access paths don’t create shadowed burrow pockets or water catchments. This lets you iterate clearances to siding, vent locations, and hose bibb routes before you dig.

room layout tool

Red Flags That Require a Pro

- Recurrent, enlarging holes within 12–18 inches of the foundation

- Cracks that widen seasonally or doors/windows sticking after heavy rain

- Persistent interior musty odor or signs of efflorescence on foundation walls

- Evidence of termites or carpenter ants despite moisture fixes

- Void under concrete steps, porch slabs, or pavers with noticeable settlement

Prevention Playbook (Seasonal)

- Spring: Inspect grading post-thaw, refresh gravel skirts, check downspouts.

- Summer: Trim vegetation 12–18 inches from the house; monitor irrigation reach.

- Fall: Leaf management to keep drains clear; close crawl vents per code and climate.

- Winter: Watch for frost heave gaps; keep snow melt directed away from the foundation.

Material Choices That Last

- Mesh: Galvanized hardware cloth (1/4 inch) or welded wire for larger burrowers; stainless where corrosion risk is high.

- Aggregates: Angular 3/4-inch gravel performs better than pea gravel for locking and drainage.

- Sealants: Class 25 or higher movement-rated polyurethane or silyl-terminated polyether for exterior joints.

Lighting and Inspection Ergonomics

- Task Lighting: A 2700–3000K headlamp with a wide beam helps you see soil texture and droppings without harsh glare. Good lighting cuts missed defects—IES emphasizes visibility and glare control for safer outdoor tasks.

- Access: Keep a 24–36 inch clear perimeter for inspection and maintenance; this spacing improves visibility and discourages nesting.

FAQ

What animal makes 1–2 inch holes near my foundation with little soil piled up?

Chipmunks are prime suspects. They leave tidy entries, often by steps or downspouts. Confirm by evening activity and faint chirps. Install a buried mesh apron and redirect water so the spot isn’t attractive.

Are small holes actually a structural risk?

The hole itself isn’t, but the pathway that channels water to the foundation is. Repeated saturation weakens soil support and can escalate settlement or freeze–thaw damage.

Can mice really enter through tiny gaps?

Yes. Mice can squeeze through openings as small as 1/4 inch. Seal with backer rod, high-movement sealant, and a metal mesh cap for chew resistance.

How far should I extend downspouts to help prevent holes forming?

Typically 6–10 feet from the foundation, adjusted to site slope and soil. Test after a heavy rain; no pooling should occur within the first 5–10 feet.

What’s the fastest humane fix for ground-nesting bees by my foundation?

Lightly moisten and compact the area, then overseed or add groundcover. Reducing bare, sandy soil removes their preferred nesting condition without chemicals.

Is gravel or mulch better against the foundation?

Angular gravel is better. It drains, discourages burrowing, and doesn’t wick moisture to siding the way fine mulch can. Keep 6–8 inches of foundation exposed.

How do I know if a hole is from erosion, not animals?

Erosion holes align with water flow—look for channels from downspouts or slope lines, and no hair, droppings, or rub marks. The fix focuses on grading, extensions, and surface materials.

When should I call a structural engineer?

If you see step cracks, doors sticking after rain, or measurable slab/stoop settlement, bring in an engineer or qualified foundation contractor to evaluate soil bearing and drainage corrections.

Will filling holes with foam work?

Foam alone is not durable outdoors and is easily gnawed. Use it only as a backing. The durable solution pairs mechanical barriers (metal mesh) with sealants and re-graded soil.

Do exterior lights attract more insects to the foundation?

Cooler color temperatures (4000K+) can attract more insects. Use warm-white (2700–3000K) and shielded fixtures to reduce attraction and improve night inspections.

What landscaping layouts minimize burrowing near foundations?

Keep plant mass away from corners, use gravel skirts 18–24 inches wide, and avoid dense groundcovers that touch siding. Prototype spacing and grades with an interior layout planner to preview clearances before installing hardscape.

Can burrows undermine paver patios next to the house?

Yes. Tunneling plus water can wash bedding sand. Edge restraints, polymeric sand, and a compacted base with proper slope prevent this and divert water away.