Can Mice Come In Through Air Bricks? Yes, and Here’s How

Air bricks are those small ventilation openings you’ll see in the walls of many homes, usually near ground level. They’re designed to let air flow under your floors and prevent moisture buildup that can lead to rot and mold.

But while they’re great for keeping your home dry and well-ventilated, they can also create an easy entry point for unwanted guests. If you’ve noticed signs of mice in your home and you have air bricks in your walls, you might be wondering: can mice come in through air bricks?

Yes, mice can definitely come in through air bricks. The gaps and openings in air bricks are more than big enough for a mouse to squeeze through. Since mice can fit through holes as small as a dime (about 6mm), the ventilation holes in most air bricks are like open doors for them.

Air bricks are usually designed with multiple small holes or slots to allow airflow, and these openings are often large enough for mice to enter without any trouble. Once a mouse gets through an air brick, it has direct access to the space under your floors, and from there, it can easily find its way into the rest of your home through cracks, gaps, or other openings.

Why Air Bricks Are Easy Entry Points for Mice

Air bricks are positioned at ground level or just above it, which is exactly where mice like to travel. Mice typically move along walls and foundation lines when they’re searching for food, water, or shelter.

When a mouse comes across an air brick during its nighttime foraging, it’s basically found a pre-made entrance to your home. The mouse doesn’t have to chew through anything or work hard to get in.

Air bricks are especially attractive to mice during colder months. When temperatures drop, mice start looking for warm places to nest and raise their young. Your home, with its warmth and potential food sources, becomes very appealing.

The space under your floors (accessed through air bricks) provides an ideal environment for mice. It’s usually dark, quiet, undisturbed, and offers plenty of places to hide and build nests.

How Small of a Gap Can a Mouse Fit Through?

This is really important to understand if you’re trying to keep mice out. Mice have incredibly flexible bodies with collapsible rib cages that let them squeeze through openings that seem impossibly small.

A mouse can fit through any hole that its head can pass through. Since a mouse’s skull is the only rigid part of its body, if the head fits, the rest of the body can follow.

For most adult mice, this means they can squeeze through holes as small as 6mm (about 1/4 inch or the size of a dime). Young mice can fit through even smaller gaps.

Most standard air bricks have ventilation holes or slots that are much larger than 6mm. Some have rectangular slots that are 10-15mm wide, while others have circular holes ranging from 10-25mm in diameter.

This means that pretty much every standard air brick on the market has openings large enough for mice to enter. Even air bricks with smaller ventilation holes can still be entry points if the mortar around them has cracked or if the brick itself has any damage.

Signs That Mice Are Using Your Air Bricks

If you’re not sure whether mice are actually coming in through your air bricks, there are several signs you can look for. Mice leave behind evidence of their presence that’s usually pretty easy to spot once you know what to look for.

Droppings are one of the most obvious signs. Mouse droppings are small, dark, and pellet-shaped (about the size of a grain of rice). If you see droppings near your air bricks, either on the outside or inside, that’s a strong indication that mice are using that route.

You might also notice gnaw marks around the air bricks. While mice don’t need to chew through the air brick itself to get in, they often gnaw on the edges or surrounding mortar as they explore the area.

Grease marks or smudge marks are another telltale sign. Mice have oily fur, and as they repeatedly use the same path, they leave behind dark, greasy streaks on surfaces. Check the edges of your air bricks for these marks.

You might actually see mice entering or exiting the air bricks, especially during dawn or dusk when they’re most active. If you’re really quiet and watch your air bricks during these times, you might catch them in the act.

Strange scratching or scurrying sounds coming from under your floors or inside your walls near air bricks can also indicate that mice have made their way inside. Mice are most active at night, so you’ll probably hear these sounds after dark.

The Problems Mice Can Cause After Entering Through Air Bricks

Once mice get into your home through air bricks, they don’t just stay in one spot. They’ll explore, nest, and can cause a surprising amount of damage for such small creatures.

Mice constantly gnaw to keep their teeth from growing too long. This means they’ll chew on just about anything they encounter, including electrical wires, insulation, wood, plastic pipes, and even concrete in some cases.

Chewed electrical wires are particularly dangerous because they can create fire hazards. According to some estimates, rodents are responsible for up to 25% of house fires with unknown causes.

Mice also contaminate areas with their urine and droppings. A single mouse can produce 50-75 droppings per day, and their urine has a strong, musty odor that can permeate your home.

These droppings and urine can carry diseases that are harmful to humans. Hantavirus, salmonella, and leptospirosis are just a few of the diseases that can be transmitted through contact with mouse waste.

Mice reproduce incredibly quickly. A female mouse can have 5-10 litters per year, with 5-6 babies in each litter. This means a small mouse problem can quickly turn into a major infestation if it’s not dealt with promptly.

How to Block Air Bricks to Keep Mice Out

The good news is that you can block air bricks to prevent mice from entering while still maintaining proper ventilation for your home. The key is using the right materials that allow airflow but keep mice out.

Wire mesh or hardware cloth with very small holes (no larger than 6mm) is the most effective solution. You want to use galvanized steel or stainless steel mesh because mice can chew through plastic, aluminum, and even copper over time.

Cut the mesh slightly larger than your air brick opening. Then, you can either fit it inside the air brick cavity or attach it to the outside using screws or strong adhesive designed for outdoor use.

Make sure the mesh is secured tightly with no gaps around the edges. Even a tiny gap can be enough for a determined mouse to squeeze through or widen over time.

Some people use expandable foam to fill gaps around air bricks, but this isn’t a good long-term solution on its own. Mice can easily chew through foam. If you do use foam, combine it with wire mesh for better protection.

You can also buy air bricks that come with built-in mesh or screens specifically designed to keep rodents out. These are a good option if you’re replacing old air bricks anyway.

Other Entry Points to Check Besides Air Bricks

While air bricks are definitely a common entry point for mice, they’re not the only way these little rodents can get into your home. If you’re dealing with a mouse problem, you need to check and seal all potential entry points.

Look for gaps around pipes, cables, and wires where they enter your home. Even a small gap around a water pipe or electrical conduit is enough for a mouse to squeeze through.

Check the areas where your walls meet your foundation. Cracks in the foundation or gaps in the mortar between bricks can provide entry points.

Damaged or missing roof tiles, gaps in the soffit and fascia, and holes in the eaves can all allow mice to enter through your roof. Yes, mice are excellent climbers and can easily scale the outside of your house.

Gaps under doors are another common problem. If you can see daylight under your exterior doors, a mouse can probably fit through that gap. Door sweeps or weather stripping can help seal these gaps.

Vents for your dryer, bathroom, or kitchen can also be entry points if they don’t have proper covers or if the covers are damaged. Make sure all exterior vents have tight-fitting covers, preferably with mesh screens.

When to Call a Professional

Sometimes, despite your best efforts to seal entry points and set traps, mice keep finding their way in. This is when it’s time to call a professional pest control service.

Professionals have the experience to find entry points you might have missed. They know all the sneaky ways mice can get into homes and can do a thorough inspection to identify every potential access point.

If you’re dealing with a large infestation, professional help is really important. A few mice can quickly turn into dozens, and at that point, DIY methods are usually not enough to solve the problem completely.

Professional pest control technicians can also identify and seal entry points more effectively than most homeowners. They have access to commercial-grade materials and equipment that aren’t available to the general public.

They can set up monitoring systems to track mouse activity and determine if your mouse problem has been completely resolved or if there are still mice getting in somewhere.

Some pest control companies also offer guarantees on their work. This means if mice come back within a certain time period, they’ll come back and treat your home again at no extra cost.

Maintaining Your Mouse Defenses Over Time

Keeping mice out isn’t a one-time job. You need to regularly check and maintain the defenses you’ve put in place to make sure they’re still effective.

Check your air brick mesh at least twice a year (spring and fall are good times). Look for any signs of damage, rust, or gaps that might have developed. Mice are persistent, and they’ll keep testing defenses for weak spots.

After severe weather, always do a quick inspection. Heavy rain, strong winds, or freeze-thaw cycles can damage or dislodge protective mesh and create new gaps.

Keep the area around your air bricks clear of debris, vegetation, and stored items. Clutter provides hiding spots for mice and makes it easier for them to approach your air bricks without being seen.

Trim back any plants or bushes that are touching your house walls. Mice use vegetation as cover and as a way to climb up to higher entry points.

Inside your home, maintain good sanitation practices. Don’t leave food out, clean up crumbs promptly, and store food in sealed containers. Even if mice can’t get in through your air bricks, you don’t want to attract them to your property in the first place.

Conclusion

Air bricks can definitely let mice into your home if they’re not properly protected. The ventilation holes in air bricks are more than large enough for mice to squeeze through, and since these bricks are usually positioned at ground level, they’re easy for mice to find and access.

The best way to prevent mice from entering through air bricks is to cover them with fine wire mesh (6mm or smaller) that allows air to flow but keeps mice out. Make sure you use galvanized steel or stainless steel mesh that mice can’t chew through.

But don’t just focus on air bricks. Mice are opportunistic and will use any opening they can find. Check your entire home’s exterior for gaps, cracks, and holes, and seal them all to keep these unwanted visitors out for good.