How to Seal Gaps & Keep Pests Out

Mice can slip through a gap the width of a pencil, and insects need even less. The good news is that the same small gaps that let them in also let your heated and cooled air out, so sealing them pays off twice. Here's where to look and what to use.

Where pests get in (walk your foundation)

Take a slow lap around the outside of the house and look low and at every penetration:

• Where pipes, cables, and the AC line enter the wall — these almost always have a gap around them.
• Gaps under and around exterior doors and the garage door.
• Where the foundation meets the siding, and any cracks in the foundation.
• Dryer and exhaust vents with missing or broken flaps or screens.
• Weep holes, soffit gaps, and where utilities meet the roofline.
• Crawlspace and foundation vents with torn screening.

The right seal for each gap

1. Small cracks and gaps around pipes: exterior-grade caulk. For gaps up to about a quarter inch, a good bead seals air and small insects out.
2. Bigger gaps and voids: expanding foam sealant fills larger openings around pipes and in rim joists. Trim it flush once cured.
3. Rodent-prone holes: pack the gap with coarse steel wool or copper mesh first, then seal around it. Mice chew through foam and caulk alone, but not metal mesh.
4. Vents and openings that need airflow: repair or add hardware cloth or screening rather than sealing them shut. Crawlspace and attic vents need to breathe.
5. Door gaps: add or replace door sweeps and weatherstripping (see our drafts guide).

Know when to call a pro

Sealing gaps is great DIY and good prevention. Bring in help when you find signs of a real infestation (droppings, chewing, nests) that needs a pest professional, when a gap is there because of rot, foundation cracking, or pulling-away siding that needs repair, or when the openings are up high or hard to reach safely. A gap caused by rot needs the rot fixed, not just filled.