The challenge is to determine how the rats gain access. They only nest in the attic, but every night they will go in and out multiple times doing what pack rats do - mainly collecting food and items of interest.
Pack rats are adept explorers, excellent climbers and can chew through wood and even lead. They can find their way into attics through the darnedest places.
They get in through open bird screens. . .
And gaps. . .
And holes . .
And exhaust vents. . .
And roof intersects. . .
At Mr. Pack Rat we have trapped, removed and excluded rats from thousands of homes. We know their tricks and we know where to look.
In about 90 out of 100 homes the entry points are obvious for us. Maybe 9.4 out of 100 are more challenging. These are usually tile roofs with areas can be quite difficult to access and inspect. We know where to look, but we can't always get to it. A rat only needs an opening 1/2 wide to squeeze through and will usually enlarge the hole to the size of a quarter or more.
Then there is that nightmare house, the 1 out of 500 that keeps us up at night. These are the houses that have the "invisible hole". Many pack rat entry points are hidden, but most can be found by moving roof tiles, using mirrors, a flashlights and the know-how of how houses are built and where to look. The invisible hole is much worse. It is both hidden and in an area where it just should not be. Usually under a tile roof, totally covered and not near any of the places you would typically look for a hole.
Here is one from last week:
A hole randomly in the middle of a tile roof. There is no rhyme or reason to it.
How did this happen? Tile roofs have another roof underneath covered with tar paper. The tile keeps the sun off the roof, but the tar paper makes the roof water-proof. Sometimes pack rats chew on the tar paper. In this case the rat chewed in just the right spot to find a tiny crack between two pieces of plywood. The crack gave the pack rat an edge to chew on and in no time chewed a hole right in the attic space.
Here is a picture of the hole from farther away:
How do we find a hole like this?
Experience and persistence. A little luck helps. Sometimes you just have to start removing tile. These invisible holes are what our nightmares are made of.