Can Mice Cause Structural Damage? What Can Happen When They Move In

by | Mice, Rodents

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Seen some holes in the shed or droppings laying around? You might have mice. When these furry rodents move in, they get up to all kinds of mischief, but can they cause structural damage?

Mice can cause severe structural damage to homes, offices, apartments, sheds, and any other types of buildings. Mice commonly chew holes in pipes, gas lines, insulation, wooden beams, retaining walls, and other materials. They also chew through electrical wiring, and often build a nest nearby, which greatly increases the risk of a fire.

In short, mice are more than pesky – they’re dangerous. In this article, I’ll shed some light on the types of structural damage mice can cause and what materials mice can get through and what they can’t.

What is ‘structural damage’?

Structural damage is any damage to a building or structure, such as an office building, house, barn, or apartment. For example, an uneven floor or cracks in the roof and walls are classed as structural damage because they are problems with the permanent building / structure. It’s not damage to what’s inside the structure or things that are movable, such as furniture.

Severe structural damage is when this damage happens to the most important parts of the structure that the structure can’t be without, such as load-bearing walls or the roof. Without a roof or load-bearing walls, the structure would break down.

Whatever the structural damage, it’s usually a costly exercise to fix.

Why mice chew so much

Photo of a mouse hiding by some leaves

Mice are born to chew, and they aren’t too fussy about what they do chew.

Mice have four front teeth – two at the top and two at the bottom. These front teeth never stop growing, so a mouse must keep on chewing on things to keep the front teeth short. If the mouse doesn’t do this, the teeth get too long and the mouse can’t open its mouth, and it slowly dies of starvation.

Mice want to avoid that at all costs.

Mice have well-developed muscles for chewing through very tough materials. These jaw muscles make it possible for mice to move their jaw forward and backward. As they gnaw on things, the teeth are grinded down but stay sharp. These strong jaw muscles also give mice the strength they need to chew enough each day to keep their teeth short.

What a mouse can chew through

If you’ve ever had a mouse infestation, it might seem like mice can chew through anything. While that isn’t actually true, mice can chew through a lot of things, like:

  • Concrete and cinder blocks that aren’t cured correctly, are getting old, or are loose
  • Drywall
  • Fabric
  • Fiberglass
  • Insulation
  • Lead
  • Linoleum
  • Low-gauge aluminum
  • Organic materials
  • Plastic (hard or soft)
  • Rubber
  • Soft vinyl
  • Wires and cables
  • Wood

Considering many structures are built with these materials, with wires and cables running through them, you can easily see how mice can quickly do a lot of damage.

What a mouse cannot chew through

When it comes to building materials, these are about the only things mice can’t chew through:

  • Concrete that’s cured properly
  • Copper and copper mesh
  • Brick
  • Steel and steel wool
  • Glass
  • Rocks

As you can see, the list of things mice can’t chew through is much shorter than the list of things they can. There’s a much greater chance that mice will cause structural damage than not.

What types of structural damage do mice cause?

Mice can do all kinds of damage to a building. Let’s take a look at the most serious types of damage to be prepared for.

Damage to electrical wiring

Photo of electric wires behind an air conditioner eaten by mice
Mice often chew holes in wires and cables, like in this picture.
Source: Mohammed El Damir, Bugwood.org

Chewing through wiring is probably the most dangerous thing mice can do because of the threat of starting a fire.

It is estimated that 25 percent of all fires attributed to “unknown causes” are probably started by rodents gnawing on gas lines, electrical wiring and matches.

Illinois Department of Health

This means that mice and their rodent counterparts, rats, are probably responsible for one quarter of all fires with unidentified causes.

Holes in insulation

Insulation is made from many different materials, but wool and polyester are usually in the mix. Wool and polyester and other materials in insulation make the perfect addition to any mouse nest, especially as a heater in the cooler months of the year.

This is one of the reasons why mice love chewing through insulation.

Insulation is there to keep your building cool in Summer and warm in Winter, so damage to it can cause temperature problems inside, and cost you a lot more in cooling and heating bills.

Holes that leak

Mice have been known to chew holes through walls and in roofs. A mouse doesn’t need a big hole to squeeze through – a quarter of an inch will do – but their holes are often big enough to let water into the building.

When the rains come, water runs in through the holes and causes even more structural damage, like a warped or rotten floor.

And if the holes get big enough, other rodents and insects will be able to get into the structure.

How to tell if you have mice

Photo of a mouse hole and mouse droppings
There are many ways to tell if you have mice. Look for tiny mouse holes in walls, close to the ground. And look for small black droppings on the floor, like the ones in this photo.
Source: Liz Kasameyer, Johns Hopkins School of Public Health, Bugwood.org

Here are the top 12 tell-tale signs that you have mice:

  1. You see mouse droppings lying around – an adult mouse leaves up to 75 little brown droppings lying around each day
  2. There’s a bad smell like something’s rotting
  3. You hear sounds like scratching and scurrying
  4. You see paw prints made by mice – mice have four toes on their front feet and five toes on their back feet
  5. You see a mouse or find a dead mouse
  6. The insulation has moved or parts are missing – insulation makes a nice nesting material and is often taken back to a mouse’s nest
  7. There are brown or yellow urine and faeces stains on the floor
  8. You see greasy trails along the floors or the walls, which is dirt left by a mouse’s body
  9. You see small pathways less than 2 inches wide in your grass or soil – mice tend to run along the same path
  10. You find a mouse hole or nest outside or in the building
  11. You find gnaw marks on furniture, parts of the building, or holes in food
  12. You find chewed up papers, wood, or other things

Is it possible to rodent-proof a structure?

Photo of holes around pipes where mice can crawl in
Cabinet under sink improperly sealed around drain and water pipes – Mice and other pests may enter the home through these openings.
Source: Liz Kasameyer, Johns Hopkins School of Public Health, Bugwood.org

It is possible to take steps to keep mice and rats out of a structure.

If you are planning on putting up a structure, you’ll find a detailed explanation with construction tips at Wildlife Damage Management.

Here are the best tips I could find to make an existing structure rodent-proof or to keep them away altogether:

  • Immediately seal any holes in walls or roofs. Put steel wool or steel mesh in the hole (mice cannot chew through this) and cover the hole.
  • Seal all holes around pipes and plumbing work
  • Make sure your bins seal tightly – nothing attracts mice and other rodents faster than rotting food
  • Keep your lawn trimmed and cut back overgrown bushes – mice love hiding in long grass and under thick bushes so predators can’t eat them
  • Make the bottom 18 inches of all outer walls smooth, so mice can’t climb up them
  • Make sure all doors close tightly

Final thoughts

Mice are backyard pests, plain and simple. They can destroy just about anything and will do so to keep their teeth short enough, find food, and build a nest.

If you suspect you have a mouse problem, deal with it immediately before you find serious structural damage or a fire starts.

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MONIQUE

Monique loves gardening and spending time in her backyard, where she grows flowers, succulents, herbs, fruits, and vegetables.

Monique spends a lot of time researching how to protect her backyard from harmful pests and trying to attract beneficial insects and animals.

She shares everything that she learns and tests here at Backyard Pests.