Locate the rat's nest and all potential entry points. Look around the inside and outside of your home for small holes, gaps and openings. Some common places to look are behind cabinets, stoves, refrigerators, basements and attic crawl spaces. Check the roof, around windows, doors, vents and the foundation when investigating the outside of the house. Rats are skilled climbers, and could access the attic from the outside.
Seal all holes with steel wool. Secure the steel wool with caulk: Rats can't chew through it. Large holes may be filled with cement or metal sheeting. These materials can be purchased at a local hardwood store. Gaps and holes that remain open will allow rats to continually enter your home.
Catch the rats by setting traps and laying poison. Read the directions carefully before using traps and poison. Mix the rat poison with peanut butter and place a dime-size amount on each trap to use as bait. Avoid attracting more rats by using more bait than necessary. Place the traps in corners, the basement, the attic and any other areas that show evidence of rodent activity.
Clean and dispose of all dead rats and their droppings. Wear plastic gloves, goggles and a dust mask for protection. Rats carry diseases that you don't won't to breathe in or expose your skin to. Sweep up all feces, throw away all urine-soaked items and clean up with a mixture of diluted bleach to disinfect and sanitize the entire area.
Thoroughly clean your entire home with ammonia. Dilute the ammonia by using one-third ammonia with two-thirds water. Scrub corners of walls, baseboards, inside cabinets and behind appliances. Ammonia is made of nitrogen and hydrogen and emits a very sharp odor. Open windows for ventilation and wear rubber gloves to protect your skin. The smell of ammonia is overwhelming to cockroaches and they typically avoid areas where ammonia has been used.
Eliminate all food sources. Store food in sealed plastic or metal containers. Clean up after cooking and eating. Wash all dishes, sweep the floor and wipe up all spills immediately. Keep pet food and water put away at night. Dispose of trash regularly and place in a plastic or metal can with a tight lid, to prevent cockroaches from feasting on the garbage.
Treat the home with boric acid. Boric acid, also known as boracic acid, is a powerful insecticide, highly effective at killing roaches. Compared to other insecticides, boric acid is modestly priced at just $5 for a 16-ounce bottle. Apply the white powder in closed-off areas, under the kitchen sink, behind kitchen appliances, bathroom cabinets, closets, the basement and the attic and inside all floor and wall cracks, crevices and gaps. Boric acid is dangerous if ingested. Do not apply boric acid where children and pets can reach it.