Gutters what to how to and common issues
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.
Effective Roof Drainage
Effective roof drainage is a must for two reasons. First, the roofing system needs to drain quickly so that large volumes of water are not trapped on the surface. Second, water runoff from the roof needs to be managed so that it is not being directed toward the foundation.
Guttering systems, like everything else, have evolved greatly over the last couple of hundred years, starting out as crude wooden troughs and ending up with the vinyl and metal systems that we use today. It is fair to say that most guttering systems are high-maintenance. Homeowners with conventional uncovered gutters are required to regularly clean out vegetation and debris that get blown into them. Gutters often need to be re-fitted when severe weather detaches them from the fascia.
Roofing gutters should slope down toward the downspout at the rate of 1/16-inch per foot, or 1/4-inch per 5 to 10 feet. An angle less than this won't allow water to move effectively, and much more of an angle will cause the water to move at too great a speed, potentially resulting in overflow over end caps and corners.
In terms of standards, home inspectors are not required to measure the amount of gutter slope. To do it accurately would be time-consuming, would require a transit or water level, and would exceed InterNACHI's Standards of Practice.
A more practical approach is to make sure that all gutters slope toward the downspout. In judging adequate slope, look for signs of standing water in portions of the gutter away from the downspout, and eyeball the margin against the fascia. It is not uncommon to see gutters installed too low on the fascia, or to see roof coverings projecting too far over the gutter. In both cases, this may lead to the water over-shooting the gutters completely. Typical gutter systems hold up better when the brackets are spiked or screwed through the fascia and into the ends of the rafters, and not just into the 3/4-inch fascia board