Why metal buildings need gutters
Metal roofs shed water and snow faster than shingles, and barns, shops and machine sheds have long, uninterrupted eaves with few corners. All of that water lands in a narrow strip along the wall. On a post-frame building, the posts are embedded in or set on the ground, and the bottom of the wall steel sits close to grade, so constant splash and wet soil shorten the life of both. Gutters carry the water to a few downspouts and away from the building. See gutters for metal roofs.
The National Frame Building Association’s design manual describes the eave as the part of the roof that projects past the sidewall, formed by rafter or truss extensions. That overhang is where the gutter hangs, and how it is built decides what the gutter can attach to.
How much water a big roof makes
One inch of rain on 1,000 square feet of roof is about 620 gallons. A 40-by-60-foot building with a typical overhang has roughly 2,500 square feet of roof, so a one-inch storm drops about 1,500 gallons, half to each eave. In a summer downpour that falls in an hour. Gutters on these buildings are sized for volume: 6-inch K-style or half-round with 3x4-inch downspouts is common, and very long or steep roofs may call for 7-inch commercial gutters. See 5-inch vs. 6-inch gutters.
Attachment: fascia or no fascia
Many pole barns have no fascia board at all; the roof steel simply ends at the eave, sometimes with a metal eave trim. Options:
- Fascia board: adding a treated or steel-wrapped fascia along the eave gives hidden hangers something solid to screw into. This is the most durable approach.
- Straps over the roof panel: roof-strap hangers slip under the panel edge and over the gutter; they work where there is no fascia but must be fastened to purlins, not just to the panel.
- Commercial brackets: heavy steel brackets fastened to the truss ends or purlins carry 6- and 7-inch gutters on larger buildings.
Hanger spacing matters more on metal buildings because sliding snow and ice load the gutter. Closer spacing, about every 2 feet in snow country, keeps the gutter straight. See gutter hangers explained.
Snow and ice
Snow slides off metal roofs in sheets and can tear gutters off or crush them. In snow regions, gutters are mounted so the front lip sits below the roof plane, and snow guards above entries and along long eaves hold snow so it melts gradually. Unheated buildings have fewer ice dams than houses, but water that refreezes in gutters and at the slab apron is still a hazard. See snow guards explained and snow load and gutters.
Downspouts and where the water goes
Long eaves need several downspouts; the University of Minnesota Extension suggests at least one per 50 feet of eave, and more is better on big roofs. Discharge should go away from the building and from the concrete apron in front of overhead doors, where refreezing meltwater makes ice. On farms, keep roof water away from the well, the septic drainfield and manure storage. Buried lines to a ditch, pond or dry well are common; a rain barrel or cistern can supply livestock or garden water. See gutters on rural homes, downspouts and icy walkways and rainwater harvesting from gutters.
Materials
Aluminum is standard. Steel gutters match steel buildings in color and strength and resist dents from equipment and hail, but they must be kept painted or coated where cut. Where copper or stainless fasteners meet galvanized steel, use compatible fasteners to avoid corrosion. In wildfire country, metal gutters and metal guards resist embers. See aluminum vs. steel vs. copper gutters and gutters and wildfire embers.
Guards on outbuildings
Barns under trees clog like houses do, and nobody cleans a 14-foot-high barn gutter often. Guards that fasten down and shed snow reduce ladder work. On open fields with no trees, strainers at the outlets may be enough. See are gutter guards worth it?
Doing the house and the barn together
A gutter crew with a seamless machine on site can run the house, garage, shop and barn in one visit, which is cheaper than separate trips. Ask for one quote that lists each building, its gutter size, downspout count and discharge. See gutters for garages, sheds and outbuildings and how to compare gutter quotes.
Costs
HomeGuide puts seamless aluminum gutters at about $6 to $12 per linear foot installed nationally and the step up to 6-inch at about $1 to $2 more per foot. Long straight runs are efficient to install; tall eaves, fascia boards added for attachment and buried drainage add cost. See our cost guide.