Unless the roof is sloped to drain over the roof's edge, there should be drainage installed for the roof system. Roof drains could be installed at the low points of the roof. Roofs should have some type of controlled method for disposing of water that collects so it discharges to the ground surface at least 5 feet away from the foundation walls, or into a drainage system. Gutters are sometimes not installed in areas that don't get heavy snow or much rain.
While roof overhangs and porch roofs protect building walls from impinging rain, gutters serve to protect building walls and the foundation from roof water runoff. Roof gutters, downspouts, and leaders or diverters form the initial components of a drainage system for the building and site. A proper design of gutters and downspouts for water-shedding sloped roof systems should be assessed during a roof inspection. Common problems with guttering are associated with installation and maintenance. Home inspectors can check if properly sized materials are being used, if guttering is appropriately sloped toward adequately sized downspouts, and if discharge is directed away from the building's foundation and perimeter. Discharging water at the building's inside corners should be avoided. Some local stormwater codes may require special filtration treatments of roof water runoff.