Professional pest surveyors inspect a building the same way every time: start at the ground, circle the walls, and finish at the roof. Follow that route around your own property and you will find the same weaknesses they do. These are the seven doorways pests use, in the order a surveyor checks them.
1. The Gap Under Your Doors
Stand inside with the lights off in daylight. If light shows under an external door, a mouse can follow it in, because 6mm of clearance, roughly a pencil’s width, is all a mouse needs. Garage doors are the worst offenders, as their rubber seals perish and warp within a few years. Fit brush strips or new threshold seals, and remember the side door to the garage that everybody forgets exists.
2. Air Bricks And Vents
Those slotted bricks at the base of your walls keep the building breathing, so never block them. Mice slip through damaged or wide slotted ones with ease, though, and so do wasps scouting cavity walls. Cover each one with a purpose-made air brick cover or stainless mesh. That will keep airflow and exclude the wildlife. While you are crouched down there, check the damp course area for crumbling mortar.
3. Holes Around Pipes And Cables
Every pipe, flue, cable and overflow that passes through an external wall left a hole, and the builder rarely sealed it perfectly. Rats and mice treat these service penetrations as front doors, particularly behind kitchen units where the waste pipe exits. Stuff gaps with wire wool and cap with cement or specialist sealant. Expanding foam alone fails, since rodents chew through it in an evening.
4. The Drains
The route nobody wants to think about. Rats live in sewers, and a cracked drain, a dry, unused toilet or a broken inspection cover gives them a path up into the building. Brown rats swim well and can pass a standard U-bend. If you hear noises under the floor or find rats indoors with no visible entry hole, the drains deserve a camera survey. Fitting a one-way rat flap inside the drain stops traffic permanently while letting waste flow out.
5. The Roofline
Look up. Slipped tiles, rotten soffits, gaps where fascia boards meet and the open ends of corrugated roofing all admit rats, squirrels and birds, and all of them climb far better than people expect. A rat scales a brick wall; a squirrel runs along a phone cable and steps off at your gutter. Loft insulation then makes a perfect nursery. Binoculars from the garden reveal most roofline faults in five minutes.
6. Windows, Frames And The Gaps Around Them
Shrunken sealant beside window frames lets ants and clothes moths file straight in, while open windows on summer evenings invite flies, wasps and mosquitoes by the dozen. Renew perished sealant with a frame appropriate product and consider fly screens on the windows you open most, especially in kitchens.
7. The Front Door, Carried In Your Hands
The seventh entrance is you. Bed bugs ride in luggage and second-hand furniture, cockroaches arrive in delivery boxes and returning grocery bags, and moth eggs hide in vintage clothing. Inspect second-hand purchases outdoors before they cross the threshold, and shake out luggage after any hotel stay.
Walking The Route Pays For Itself
This 7 point circuit takes under an hour twice a year and prevents the majority of infestations before they start. When you find evidence already inside, droppings, gnawing, smear marks along skirting, the calculation changes, and experienced pest controllers in London can trace an active infestation back to its entry point with smoke tests, tracking dust and drain cameras, then seal it properly. Find the doorway first. Everything else in pest control follows from that.