Once mice have been treated, proofing is what actually stops them coming back. Mice can fit through a gap roughly the width of a pencil, so “small” gaps matter far more than they seem. Here’s a room-by-room checklist.

Kitchen

• Gaps around pipework under the sink, sealed with expanding foam or a proper pipe collar
• Gaps behind and beside built-in appliances (ovens, dishwashers) where they meet cabinetry
• Skirting board gaps, particularly at corners and where boards meet the floor
• Any gap where worktops meet the wall

Utility Areas and Boiler Cupboards

• Pipework entry points where they pass through external walls
• Gaps around boiler flue housing
• Any airing cupboard access points behind or beside the boiler

Exterior and Air Bricks

• Air bricks fitted with a proper mesh guard (not blocked entirely — they need airflow, just not mouse access)
• Gaps where extensions or conservatories meet the original structure
• Damaged or missing pointing in brickwork near ground level

Doors and Windows

• Gaps under external doors — a proper draught excluder often doubles as a mouse barrier
• Gaps around older single-glazed window frames, particularly in period properties
• Garage and shed doors, which are common secondary entry points into an attached structure

Loft and Roof Access

• Gaps where roofline meets brickwork
• Vents fitted with mesh rather than left open
• Any gap around where cabling or aerials pass through the roof

What to Use to Seal Gaps

• Wire wool or coarse steel mesh stuffed into gaps before sealing — mice can chew through expanding foam alone, but not steel wool
• Proper pipe collars for pipework penetrations, rather than just foam
• Mesh guards for air bricks and vents, which need airflow but not mouse access

When to Do This

Proofing works best once current activity has been treated and confirmed stopped — sealing entry points during an active infestation can occasionally trap mice inside rather than keep them out. Your technician will confirm the right timing for your specific situation.