General Information

In typical construction, downspouts are spaced from 20 feet to 50 feet with a 60-foot maximum. The final routing of the roof water may determine whether a small gutter with many downspouts will be more feasible than a large gutter with few downspouts. House-sized gutters are readily available. But in many rural locations, specially formed gutters may be quite expensive. Gutter hangers are normally spaced 3 feet on center (o.c.).

In an environment with broad temperature changes, the gutters need to move without being restrained by the hangers. An alternative is to build the gutter with shorter lengths, allowing a space between sections for expansion. Table 1 shows the thermal expansion/contraction of a 100-foot length of gutter with 100 degrees of temperature change.

It is estimated that the annual runoff from a 40- by 80-foot barn roof near Folsom, La., will average about 60,000 gallons. Uncontaminated roof water can be discharged into the waters of the state or stored for farm use, such as watering livestock. Frequently, dairy barns present special problems because of their huge roof areas that require large gutters and downspout capacity.

Positioning gutters to reduce snow and ice slide failures may be a major consideration. If the building eave-line has a 2- to 3-percent slope, gutter capacity is increased compared to gutters mounted nearly level. Most gutters are mounted level for appearance, but a slope of one-sixteenth inch per foot is desirable for drainage.

An alternative to roof gutters for buildings with at least a 12-inch overhang and where an open channel will not be polluted is a surfaced channel or a stone-lined, tile-drained ditch alongside of the building. Also, an open channel could conduct water from a small gutter with multiple downspouts.