The only reason raccoons or squirrels take up residence in your attic is to have babies. The reasons they have selected YOUR attic is that they could gain access and that they feel that YOUR attic is the safest place to keep their babies---it is your mission to convince them otherwise!
Here are three effective means to convince unwanted attic occupants that YOUR attic is NOT a safe place for their babies:
PREDATOR SMELL. Place a stinky dog blanket (the smellier the better) near or as close to the area of animal activity in your attic. Purchase fox urine at sporting goods stores, saturate some tennis balls with it and toss in the attic.
MAKE A LOT OF NOISE. Periodically, over a 3 day period, go into the attic and make a lot of noise. Blow whistles, honk air horns, and clang pots and pans. You can also attach a box or cans to a cord, toss it into the attic, and drag it across the rafters. Make the noise during the sleep period of the animal (raccoons sleep during the day; squirrels at night).
LIGHTS. Keep bright lights on in the attic or run trouble-lights 24 hours a day for the 3-day period.
Utilizing all three of these methods will assure you of a critter-free attic in about 3 days.
The raccoons/squirrels will move their babies (one by one) to a new nest. Raccoons will move their babies during the night and squirrels during the day. Give them ample opportunity to do this. Do not block entrances/exits and make sure to keep your dogs inside as much as possible. NOTE: This technique does NOT work for mice/rats. This technique should not be used for owls since a mother owl cannot move her babies.
Your job is NOT yet complete. You must now repair the animal's access to your attic. Block entryways with thick boards or wire and trim back tree branches. Other squirrels and raccoons are waiting to take up residence in your attic, so act quickly. This method of removal has been used hundreds of times over the years in the Montgomery county area and has proven 100% successful.
Lastly, trapping is a very ineffective way to deal with raccoons/squirrels in attics. You may be able to trap the mother but it is almost always impossible to trap the babies. The babies will die in your attic. Also, studies show that trapped raccoons and squirrels released into new areas have low survival rates.