Raccoons are a common wildlife nuisance. They harbor in culverts and drainage ditches before entering buildings, attics and chimneys, often through gaps in extended windowpanes. Female raccoons may breach attic screens or roof vents to gain entry, to establish dens to bear young. Sometimes raccoons rear young in separate areas, and may remove and displace young as needed. Unlike other wildlife, raccoons make latrines, meaning they lay their waste material in one spot.
Limit access to rooftops by removing overhanging branches. Exclude chimneys by securely fastening a commercial cap of sheet metal and heavy screen over the top of the chimney. Young may be present April through August, so before evicting adults to make repairs, make sure no young are present. Cages used for trapping should be larger, approximately 10x12x32 in.
— Dr. Reid Ipser, Director of Technical Services, Nisus Corp.