It is not possible to control some pests without eliminating their ability to get in and out of a structure. Physical alteration of a structure is referred to as exclusion or build-out. Pests will always return if there is easy access.
Exclusion is an art form. It is a building specialty just like being a finish carpenter or a cabinet maker. In 25 years I have seen very few main stream contractors do it well and even fewer home owners. It’s not just a matter of the materials used, it is also the method of attachment, and the structural tolerances allowed.
Exclusion for rodents: AKA: Rodent build-out, Rodent proofing, Rat exclusion, Mouse exclusion
Rodents have teeth that can chew through anything softer than steel. Proper build-out materials to be used with rodents include:
Quarter inch galvanized metal screen mesh, sometimes referred to as hardware cloth. This material, in the proper thickness can no longer be found at your large neighborhood home improvement warehouse, but can often be found at farm supply stores and co-ops. Concrete, mortar, or concrete patch, a ready made concrete patch which often works very well can be found in the paint aisle of your local home improvement store. Metal flashing, or strapping metal; make sure that you do not purchase or use the softer, aluminum flashing which rats will sometimes chew through. Solid wood, reinforced with screen or flashing if necessary; it is not unusual for rats to chew on a 2X to enlarge a gap which gives them access. Brass wool, or Stuff-It; does not rust and works well, but only tightly packed in small gaps. Steel wool – but only as backing to fill large gaps, it should be covered over with concrete, mortar, or concrete patch.
Materials that should not be used for rodent proofing:
Expanding foam insulation is not only soft and easy to chew; rodents like chewing on it and are attracted to chemicals in the foam. Steel wool rusts and can be pushed or pulled out of large gaps, it should only be used as backing for concrete patch or mortar. Cedar, other really soft woods, or any thin non-reinforced wood in areas of high activity
Keep in mind that mice can squeeze through openings as small around as a dime and rats through an opening as small around as a quarter.
Exclusion for birds:
Birds are not usually as destructive as rodents – but often involve the use of tall ladders, and knowing what you are doing can make the difference between and attractive or at least non-obtrusive solution and an unsightly and / or a non effective solution.
Quarter inch galvanized metal screen mesh, sometimes referred to as hardware cloth. Metal flashing. Solid wood, reinforced with screen or flashing if necessary
One final note about exclusion: There is nothing more expensive than paying to have work done, finding out later the work was not done properly, and then having to pay for it to be done all over again.
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Step 1: Gap between metal furnace base and concrete foundation. Gap about the size of a pad of steel wool.
Step 2: Steel wool stuffed into gap, situated about a half inch or so into the opening. This will provide a backing for the concrete patch so that the opening can easily be patched.
Step 3: Concrete patch is applied to the exterior of the gap. This closed off a gap that was allowing rodents to enter the garage around the furnace. Mice need a 1/4 inch gap or a hole as big around as a dime.
Note base of drain pipe covered with heavy duty 1/4 inch mesh screening / hardware cloth. The plastic pipe is vulnerable, as is the expanding foam at the top of the pipe, neither were installed by us. As this is on the exterior and it easily monitored, it should be a snap to tell if rats try to chew through the vulnerable areas.