One of the most common ways for rodents to enter an attic is through a gap between the shingles and the gutter. Gaps like this are extremely common in Washington State due to a quark in the residential building code. This gap, sometimes called a carpenter’s gap or construction gap, can be sealed off using a piece of metal flashing called a drip edge. This piece of metal is also known as gutter flashing or rake edge flashing.
How to check for drip edge flashing
If you’re stumped on how mice, rats, birds, or squirrels are getting into your attic, we highly recommend looking at the exterior of the roof line. If you have a hipped roof (shaped like a pyramid) you should check the entire perimeter. If you have a gabled roof you likely only need to check the two sides with gutters.
Slide your hand to the back of the gutter where it’s secured against the house. If you can fit your hand under the shingles it’s big enough for a rat to squeeze through. Remember, rats only need a gap the size of a quarter and mice only need a gap the size of a dime. Rodents usually leave signs on the areas they frequent the most. Look for chewing, greasy smears called rub marks, and of course droppings.
Drip edge wasn’t in Washington code until 2015
Washington State residential code only began requiring drip edge in 2015, meaning If your home was built in 2014 or earlier, there is a good chance you have a large gap running continuously around the perimeter of your roof. You can read the code yourself online.
Should you install drip edge flashing to seal the attic from rodents?
Yes, you should definitely install a drip edge (AKA gutter flashing) to seal out mice, rats, squirrels and birds. At a cost of $10 to $20 per foot installed, it’s fairly inexpensive and will save you money down the line compared to the cost of damage from an infestation.
In addition to blocking pests, drip edge flashing protects your house from wind and water dripping behind the shingles, hence the name “drip edge.” It’s a wise investment for any roof.
A poorly maintained home on the block (we know you know the one)
A chicken coop nearby
It’s like the old adage, “You don’t have to run faster than the bear, just faster than your friend.” You don’t have to make your house mouse-proof, you just have to make it less attractive than your neighbor’s house. Mice will go where it’s easiest to get water, food, and shelter.
Natural ways to reduce interest from mice…
Bungee your garbage bins to keep the lids snug
Seal food in airtight containers like glass canisters
Clear a 1 foot perimeter around your house, including brush, wood piles, rockery, etc.
Remove standing water like bird baths
Clean up dog poop since it is full of protein, carbs, and other things mice like to eat
Keep bird seed off the ground by investing in a rodent-proof bird feeder and installing it at least 6 feet from “launch pads” like fences or trees
Trim fruit trees and berry bushes on the bottom and sides to prevent rodents coming up for a snack
Step 2. Seal up your house
How to find mouse entry holes
Check your utility lines to ensure pass-through holes are snug:
Sink supply and drain lines
Plumbing stacks on the outside of the house
Gas lines coming into your kitchen or laundry room
Electrical lines, particularly through exterior walls
Verify all utility vents have tight wire mesh and snug pass-through holes:
Bathroom fan vents
Kitchen fan vents
Weather-proof your doors:
Garage doors should have weather stripping to close gaps
Cracks in concrete pads (such as the area below your garage door) should be filled for a seamless seal with the door above
Exterior doors should hang plumb and square so they seal tightly
Scope out your roof for easy access points, then double down on wire mesh:
Dormers have complex joints between shingles, fascia boards, and windows that require precise cuts to stay mouse-proof. Time and poor craftsmanship can create gaps.
Attic vents are necessary to keep moisture at bay but can decay with time. Wasp nests, bird nests, and other animal activity can also puncture your vent grates.
Chimney caps are metal boxes that cover the hole at the top of your chimney. Check yours for gaps or rust. If you don’t have one, buy one for less than $100.
How to install wire mesh for mouse-proofing
Select your wire mesh: Pick a mesh with quarter inch holes and make sure it’s easy to bend. We recommend galvanized mesh since it has a special coating to resist rust, making it last longer. You can buy products like this at most hardware stores for about $10.
Select your screws: The ideal screw for installing mesh has a large head so it doesn’t pass through the holes in the wire. Again, we recommend galvanized screws to resist rust. Try to keep the length to about an inch and keep the diameter to a minimum. Using a oversized screws means making oversized holes in your house.
Installing your wire mesh: Cut a section of wire that extends at least an inch beyond the edge of the hole in all directions. Bend the wire so it fits snuggly inside the corner or around edges. If there is slack in your mesh the mice will simply push under it. Anchor the mesh with screws, about one every four inches. When on your roof, DO NOT anchor directly into your shingles or you risk creating a leak.
Can you use spray foam or steel wool instead of wire mesh?
Yes, but we don’t recommend it.
Step 3. Trap mice already in the house
There are two key factors in making sure you’ll get rid of mice naturally– picking the right trap and placing it properly. No matter what type of trap you use we recommend baiting it with peanut butter. It’s cheap, natural, and incredibly tempting to mice.
Why you shouldn’t use poison baits
By far the most common type of mouse bait is an anticoagulant rodenticide. That’s a fancy way to say that it thins the animal’s blood, causing them to bleed out and die slowly.
It’s cruel to kill the animals slowly over time.
Poison has terrible consequences for predators that eat mice like urban owls and your neighborhood cat.
The mice die in your walls. Some pest control companies claim the mice become thirsty, seek water, and then die outside. This is nonsense.
Get more information on the negative impacts of rodenticides from the Audubon Society.
So why are poison baits so common?
Traditional pest control companies rely heavily on poison bait because it is cheap and any employee can do it without training. Setting out a bait box is faster and simpler than doing an inspection, sealing entry holes, and setting traps in strategic locations.
Types of all-natural mouse traps
T-Rex snap traps are reliable, humane, & reusable
The plastic T-Rex snap trap from Bell is a highly sensitive trap with interlocking teeth. They are much heavier than a traditional wooden trap so they stay put. You can also wash and reuse the traps indefinitely, so they are more eco-friendly than disposable traps. The plastic teeth have a lot of force, making for a quick and humane death. The traps have small holes in the base so you can feed a zip tie through and secure the traps on vertical pipes and beams. Parker Eco Pest Control uses these traps exclusively (and no, they didn’t pay us to say that!).
Wooden snap traps are tough to set properly
Victor mouse traps are the stereotypical trap you see in the movies baited with a piece of swiss cheese. Setting these traps involves pulling back the pin carefully, setting the bait, and putting it in the right spot without triggering it. They’re pretty finnicky and go off without catching a mouse often, especially compared to the T-Rex.
Glue traps can be cruel
Glue traps come with a lot of well-deserved horror stories. Mice have been known to languish in the glue, starving to death. They sometimes chew off their own legs to free themselves. If you opt for a glue trap we suggest you use it ONLY under close supervision. As soon as you catch a mouse you should either:
Put on gloves and wipe the mouse down in olive oil to free it from the trap. Set it free outside.
Fill a bucket with water and drop the mouse and attached trap in for a quick death.
Live traps require daily supervision
If you can’t bring yourself to kill a mouse you might lean towards live traps. Simply place a tasty treat inside and let the door snap shut once the mouse is inside. Traps like this MUST be checked daily or you risk leaving a mouse to die slowly from starvation – this is far worse than a quick death from a snap trap.
Where to put the traps
The simplest solution is putting traps where you find the most evidence of activity like droppings, urine smells, or rub marks.
There is some finesse to how the traps are positioned. Mice are neophobic, meaning they are suspicious of new things. You need to make it as easy as possible to stumble into the trap. Look for narrow paths next to walls and hidden corners. Do not waste your time by simply opening your attic door and setting a trap on the open space inside.
Step 4. Natural mouse control outdoors
The A24 from Goodnature is a self-resetting trap that kills 24 mice with a single cartridge. Set it up outside, sit back, and wait. Parker Eco Pest Control will gladly install one.
Owls eat as many as 12 rodents a night! Installing an owl box gives you about a 50% chance of getting an owl every nesting season. Learn more about owls for natural mouse control on our blog.