Most people use steel wool or spray foam to stop mice from entering their home. These often work to solve the immediate need. But it looks sloppy and it doesn’t keep them out very long. There are some very effective professional exclusion products that we utilize in our repairs. While this article will not cover the art of professional rodent exclusion, it aims to provide you with the information to make a better, long lasting repair using store bought materials.

You might want to remove the rodents before you seal your home. Then monitor for new activity after the home is mouse proofed.

So how large of a hole can a mouse enter? A mouse can contort its body to fit inside an entry point that is 1/4″ in diameter. That is amazingly small! I think they say the size of a nickel. A man’s pointer finger is just about the diameter hole that a mouse can squeeze through.

Begin by inspecting the most obvious places first. Sometimes it is an easy plug. Other times you really have to dig.If your home is constructed with brick, you might have more difficulty finding the entry points. Also, if you have a ranch, you may have to reach new heights. Mice might not be entering from cracks along your foundation. They can climb up houses and enter the home from rather high up. Brick and stone facades make it more likely that there are elevated entry points.

Places to Look

Along the Foundation Walls

The easiest place for a mouse to enter a home is along the foundation walls. Foundation walls are constructed of clay block, cement block, and stone. Foundation walls can consist of a brick outer wall with structural block behind it. Foundation block is connected with joints of mortar. It is common to have mortar deteriorate overtime. If the breaks in the mortar are significant, deep enough and larger than 1/4″, mice can enter through these points.

Foundation walls raise up only a few feet from the ground, making this the most common point of entry. They can even contain purposely constructed weep holes that make it a simple task for mice to pop right in. If mice are in the basement, consider areas around the foundation as the first suspect.

Around Entry Door Garage Doors and Basement Windows

These are biggies. For homes with attached garages, repairing the garage door weatherstripping should be your number one priority. Even if it looks good across the length, go to the end points of the rubber weatherstrip. On each end of the door, there is almost always gaps existing perfectly to allow mice entry into the structure.

Check around the framework of entry doors. Look below the threshold. If anyone has ever installed a new door in an old house you can understand how this is a common issue. Significant gaps between the door frame and the actual frame work of the home are common. Underneath the door threshold, there can be a mailbox size void all the way down to the sill plate. Often the only thing that separates mice from these voids are molding and a line of caulk. Wood surrounding a door rots or the caulk seal wears out over time. When this happens, mice can enter. Chipmunks also like to enter underneath entry door thresholds. These rodents often nest close to these points in the wall insulation, or in the insulation stuffed along the sill plate.

Under Porches, Decks and Stairs

Nearly every mouse proofing job performed has entry points in these areas. A lot of the time there are gaps in the foundation block underneath porches and decks. No one ever goes under there porch. Over time, this neglected area can deteriorate. Mice love coming and going in low traffic areas under porches and decks.

A ledger board is used to attach a porch or deck to a home. This strip of dimensional lumber is bolted horizontally across the home. Inspect this, and any structural supports connected to the home. Since lumber surrounds these gaps, a wire mesh screen stapled in place over these gaps, provide a quick and easy fix.

People with poured concrete steps have problems when the steps settle away from the home. This leaves a gap for rodents to squeeze behind and find a vulnerable point of entry in the actual foundation. Properly repairing gaps behind prefabricated concrete steps can be an difficult since the steps need to be pulled away from the home for access.

Behind Siding

There are 3 main types of siding: Wood, vinyl, and aluminum. Each one has its own weak spots. You will want to stick your fingers behind the bottom row of siding and run them along the entire perimeter of the home. The bottom row of siding should sit flush against some form of backing. There are a number of materials that may be used behind siding. These materials may have fallen out in spots, or there may be gaps between pieces from when it was installed.

Sometimes siding has less than a finger gap all the way around the house. The foam board insulation, expansion board or plywood backing may be intact all the way around the home behind the siding. It is not until the corners that you find the problems. Aluminum and vinyl siding have corner pieces. These are usually hollow tubes that give rodents a vertical runway up the house. Not good. If you hear mice in the walls, false soffits, and attics, this is a good reason why.

Anywhere Up

Yes mice can go vertical up a textured wall surface, like brick. They can also climb up gutters. If you have a brick home, a home with a stone facade, or a ranch, look up for entry points. With brick, the entry points can vary greatly. Many new homes have stone facades on the front of the home. Where these columns meet the next section- there can be issues. The top row of stone usually meet a row of aluminum that transitions into the soffit. Other times, there is a wood framework above the stone facade.

On buildings with low roofs, they frequently enter through attic/ roof ventilation. Power ventilators are the most common culprits. They are almost never screened properly. Other places to look up at are the molding below the gutter, junction points of different sections of roof, fascia board behind gutters, and other types of framing/junctions. Gable and soffit vent screens usually deteriorate over time allowing insect, bird and rodent entry. Birds love gable vents with deteriorated screening.


Crawlspaces can complicate rodent proofing greatly. There are some homes in the Cleveland area that have a crawlspace under the entire home! Check weep holes and crawlspace ventilation for proper screening. Also inspect the junction where the crawlspaces attach to the original portion of the home.

How To Plug a Mouse Entry Point

Any gap larger than 1/4″ needs to be sealed. But how do you seal a hole once you find it? There are many different materials that can be used. What is the best choice? The best way to plug an entry point is to match the product with what was originally there. That way you don’t have caulk in your mortar and foam in your caulk.


If the mortar between the wall blocks is significant, tuck pointing walls may be the proper procedure. You will want to match the new repair with the color of the existing mortar. This can is sometimes best left to a professional. They sell mortar repair in tubes to be applied with a caulk gun. This might be the easiest option for home owners. For large tuck pointing jobs, we refer our customers to British Stoneworks of Lakewood, OH.

Spray Foam

When you have a rodent hole, it is very easy to fill it up with a can of spray foam. While this is a valid option to fill voids, it should only be used as a filler or backer. Foam should be sealed over because rodents can gnaw through it. It is also not a good option for kitchens since it is porous and can create an unsanitary condition. For homeowners you can purchase Great Stuff Pest Block. It has a taste repellent inside of it. That works to deter gnawing but it will not stop a rodent from digging it out. When applying foam, is it important not to overfill. Spray foam expands. If it does over expand you can push it back in before it completely cures. Otherwise you can return after it is hard and cut the excess off.

Exclusion Material

Homeowners can use 1/4″ hardware mesh as the best option along with a high grade sealant. Steel wool is okay to use inside where it will not get wet. Steel wool will rust outside and stain the building material underneath. The material will also shrink and corrode making it useless. Aluminum screen that is sold for windows and doors can be folded and stuffed into holes. Rodents can chew through it so it is not ideal in certain instances. Overtime it will become brittle and lose effectiveness.


Rodents can push exclusion material out of holes sometimes. Therefore a high grade sealant should be used to hold it in place. This also seals the repair. Sealant color can be matched to the existing surface to blend it in nicely. Sealants are different from caulk. Caulks are not resistant to rodent gnawing. Sealants are formulated to bond to building material, not crack or shrink, and harden for a more permanent repair.

The Sandwich Effect

Fill a void with spray foam. Then use a layer of exclusion material and press it into the uncured foam. The foam will lock it into place on the backside. Then you can use a sealant (not caulk) to use on the outer surface. It creates a sandwich effect that is very effective.