A house mouse can compress its body through a gap the diameter of a pencil — approximately 6mm. Rats require roughly 19mm. These are not large openings, and they exist in virtually every residential structure built before modern construction standards: the gap where a pipe enters a foundation, the compressed corner of a door sweep, the open space behind an exterior dryer vent, the crack where a settling foundation has separated from the sill plate. Exclusion work identifies and seals these entry points systematically, a process that is labor-intensive but provides permanent results.
The Most Common Entry Points
Professional exclusion inspections focus on the areas where structure meets exterior: foundation gaps, utility penetrations (pipe, conduit, cable entries through walls and foundation), door and window perimeter gaps, garage door seals, weep holes in brick construction, roof line gaps at the junction of soffit and fascia, and the open space inside hollow block foundations. Rural Missouri homes with crawlspace foundations present additional entry opportunities at the crawlspace access doors, vents, and the sill plate junction that are less common in slab construction.
Exclusion Materials by Application
| Material | Best Use | Notes |
|---|---|---|
| Copper mesh (Stuf-Fit) | Pipe gaps, irregular openings | Rodents won't chew through; flexible for irregular shapes |
| Hardware cloth (½" galvanized) | Vent covers, crawlspace openings | Durable; use 19-gauge minimum |
| Foam + hardware cloth | Large foundation gaps | Foam alone is not rodent-proof |
| Door sweeps (heavy-gauge) | Door bottom gaps | Brush-style survives uneven thresholds |
| Sheet metal flashing | Garage door corners, sill gaps | Permanent; requires fasteners |
| Concrete/mortar | Foundation cracks, block voids | Best for permanent structural repairs |
Rural Missouri Exclusion Considerations
Rural properties present exclusion challenges that suburban homes typically don't face. Older construction with stone or mixed-material foundations has more gap complexity than poured concrete. Homes surrounded by agricultural fields face persistent pressure from field mouse populations that spike after harvest when cover is removed. Properties adjacent to wooded land maintain year-round pressure from deer mice and woodland species. In these environments, exclusion is particularly valuable because no bait program can keep pace with the reinfestation pressure from adjacent habitat — the source must be addressed at the structure.
D&D Pest Control serves Franklin County and rural Missouri for rodent exclusion as part of their rodent management programs. Visit ddpestcontrolmo.com for service information, or find providers in our Missouri directory.