There are a common series of basic steps that experts recommend for dealing with rats in the attic. The first step is to discover the rat's entryway and make it impossible for it to get back inside, which may even take professional help from an exterminator. Once that's finished, you'll need to deal with the rats left inside. There are many different ways to do that, and choosing your own method will depend on your moral stances and other issues. After the rats are gone, many experts recommend taking extra measures to clean up around your property and inside the attic so other rats won't be attracted to the scent of the rats that used to live there.
The reason it's common to find rats in the attic is because of a particular breed of rat called the roof rat or black rat. These animals like to live in trees and are prone to climbing. Living in an attic is a relatively natural thing for them, and it has some advantages, including access to human food, safety from predation, and shelter from the weather. Roof rats are very common in hot areas, and are especially known to cause problems in the southeastern part of the United States.
The type of extermination method used for dealing with rats in the attic will often vary depending on your belief system. Some people are very particular about harming animals in any way, and they might choose to use no-kill traps that capture the rats alive. These rats will generally be transported out into the woods and released. According to experts, this method can work very well.
There are also other methods such as poisoning and snap traps, along with some more exotic solutions. Poisoning can be effective, but rats rotting in a person's attic can produce an unpleasant smell, and many people believe that poisons are inhumane. Snap traps are probably the most popular technique because they kill rats instantly and allow the person to dispose of the corpse easily. Most experts recommend snap traps as the most effective method of dealing with rats for those who plan to exterminate them instead of releasing them alive.
One common piece of advice among experts for dealing with rats in the attic is to beware of re-invasion. Rats have a great sense of smell, and roof rats tend to flock together in big groups. It's very possible that your roof will have a subtle rat smell even after your rat problem is dealt with, so it's considered wise to clean very well to remove any rat residue.