Direct Field Answer: The top 3 rodent entry points in San Gabriel Valley homes are corroded foundation crawl space vents, roofline fascia gaps at gable junctions, and unsealed AC/utility wall penetrations. Rats require a 1/2-inch gap, while mice squeeze through 1/4-inch voids.
After inspecting hundreds of properties in Covina and the surrounding San Gabriel Valley, certain entry points appear on nearly every job. Some are predictable. A few routinely surprise even homeowners who think they know their property well. Performing a professional rodent inspection is the only way to uncover hidden structural gaps.
Here are the ten we find most often — what to look for and why each one requires permanent rodent exclusion and proofing.
1. Foundation Vent Screens
Every house with a raised foundation or crawl space has foundation vents — small rectangular openings that allow airflow under the house to prevent moisture buildup. The original galvanized screens on homes built in the 1940s through 1970s commonly corrode, warp, or come loose from their frames. When the screen goes, the opening is typically 4 to 6 inches wide — more than large enough for any rodent species.
What to check: Push on the screen. If it flexes significantly or falls inward, it's not properly secured. Look for rust, holes, or gaps at the edges of the frame.
2. Gaps at Roof-Wall Junctions
Where the roof sheathing meets the exterior wall — particularly at the tops of gable ends and at corners — there are often small gaps that weren't fully sealed during original construction or became exposed during re-roofing work. Roof rats exploit these exclusively, approaching from trees and power drops.
What to check: Use binoculars to examine your roofline from ground level. Look for dark gaps or openings at the point where the roof edge meets the wall, especially at corners and under the overhanging eaves.
3. Plumbing Penetrations
Everywhere a pipe enters or exits your home's structure — under sinks, where the water main enters the foundation, at the base of toilet flanges, around shower drains — there's a gap between the pipe and the surrounding material. New construction sometimes fills these with spray foam (which rodents chew through). Older construction often leaves them open.
What to check: Look under every sink cabinet at the back wall where pipes enter. Feel around the base of pipes for gaps. Check the area where the water heater's supply and drain lines enter the wall or floor.
4. Garage Door Seals
The rubber or vinyl seal along the bottom of a garage door hardens, cracks, and compresses with age. Gaps along the bottom seal — even small ones — are a primary mouse entry point. Side seals at the door frame also deteriorate and create vertical gaps along the edges.
What to check: Stand inside the closed garage at night and look for light penetrating around the door perimeter. Any light = any rodent.
5. Weep Holes in Brick Veneer
Homes with brick exterior veneer have small gaps left intentionally at the base of the brick — weep holes — designed to allow moisture to drain out of the wall cavity. These holes are exactly the right size for house mice. Many older homes with brick veneer have no screening over them at all.
What to check: Walk along the base of any brick wall and look for small rectangular openings in the mortar joints at the lowest course of brick. Unscreened weep holes are a direct mouse highway.
6. HVAC and Mechanical Penetrations
Air conditioning refrigerant lines, electrical conduit, cable and internet lines, gas pipes — everywhere a contractor drilled through your wall, there's a gap around the line. Spray foam is typically used to fill these, but foam degrades and shrinks over time.
What to check: Walk the outside perimeter of your house and examine every point where a line, pipe, or conduit enters the wall. Pay particular attention to where the AC lines enter and to cable lines — these are often installed by subcontractors who don't prioritize pest-proofing.
7. Attic Fan and Turbine Vents
Attic fan housings and turbine vents that penetrate the roof deck often have gaps around their base where they connect to the roof surface. Flashing can lift, sealant can crack, and the fit between a vent housing and the roof deck is rarely perfectly tight. These are high-value entry points because they open directly into the attic — roof rats' preferred destination.
8. Utility Room Walls
In older Covina homes especially, utility rooms housing the water heater, furnace, or laundry often have partial walls or cabinets with gaps at their base connecting to crawl spaces or sub-floor areas. Once in the utility space, rodents have access to wall voids throughout the house.
9. Overhang-to-Soffit Gaps
Where the exterior soffit (the underside of the roof overhang) meets the exterior wall, there's often a gap — particularly at corners where two planes of soffit meet, and on homes where the soffit material has warped or pulled away. We find open soffit gaps on a significant percentage of homes in Covina's older neighborhoods.
10. Damaged or Absent Door Sweeps
This applies to side doors as well as the main entry. Any exterior door without a functional door sweep — one that actually contacts the threshold when the door is closed — has a gap at the bottom. For mice, which only need a quarter-inch gap, many "functionally fine" door sweeps are operationally useless.
If you want a professional assessment of your property's entry points, call (626) 540-1091. Our 30-point inspection covers all of the above and more in San Dimas, Azusa, Covina, and throughout the SGV. You can also view our pricing guide to see costs for complete exclusion repair.