No two buildings — or gutter systems — are exactly alike. Whether it’s a shopping mall or country club, a large estate or a neighborhood home, every guttering project has specific needs. And though 5- and 6-inch gutters are industry standards, factors ranging from architecture to geography can affect decisions about proper sizing.
“Start by looking at the roof line,” advises Bruce Andrews, owner of Bruce Andrews Seamless Gutters/Gutter Helmet in Maiden Rock, Wis. “When you see the number of squares of shingles, it will tell you how many gallons of water can come off of the roof during a storm. The bigger the roof the more water it will generate.”
Since gutters exist to drain water away from buildings, then estimating the amount of water a gutter must potentially carry is a key to determining the correct size for the trough. But Dan Vitale of Vitale Seamless Gutters in Somersworth, N.H., says in addition to the size of the roof, “Slope is another important factor to consider.” His own rule of thumb is 6-inch gutters for most commercial projects and 5-inch for most residential jobs. Yet different conditions may require an adjustment in gutter size.
A third consideration is the downspouts. “You should worry more about your downspout sizes rather than your gutter size,” advises owner Doug Craig of Viking Metal Products in East Point, Ga. Happily, he points out, the first chapter of the Sheet Metal and Air Conditioning Contractors National Association (SMACNA) gutter manual “has in detail the maximum rainfall for locations around the country, so that you know how many square inches of rainfall to plan for each downspout.”
Size-specific solutions
Since Andrews’ crews perform both residential and commercial work, they must know what to look for at each jobsite. Based on the SMACNA manual’s data regarding expected rainfall, he notes, “We might see that 5-inch gutters need an extra-large downspout. In the Midwest, for example, you can have everything from a steady all-day rain to a half-inch downpour in a few minutes.”
After sizing up the gutters, Andrews continues, “When we get to a house, we make sure the drainage is right.” Even if gutters are the correct size for the project, an improperly installed gutter system can cause overflows, backups, blockages, ice damming and other problems.
Andrews has also encountered projects where the steep pitch of the roof necessitated extra downspouts. Yet the decision is not always cut-and-dried. “Whenever possible, we hide the downspouts and try to keep the aesthetics of the building in mind,” he explains. One way to balance function and appearance, he suggests, is to “maintain the look the customer wants by using colors that match as closely as possible, so that the work blends into the building.”
The demands of form and function sometimes require a combination of 5- and 6-inch gutters. “We’ve done some large sheds and used 5-inch gutter on smaller overhangs and then 6-inch for longer runs,” Andrews reports. “But since the different sizes weren’t installed close to each other, it maintained the look of the building.” Depending on the job, Bruce Andrews Seamless Gutters might use larger downspouts — or more downspouts — for the bigger gutters on a job where both 5- and 6-inch styles are used.
Whatever size gutter is needed, Andrews adds, “You must have a splash guard for every valley.”
Estimating by experience
Vitale Seamless Gutters is a full-service residential and commercial installer. Through his 15 years of experience on projects of every building type, Vitale has learned, “Each house, each roof size, each fascia board is different. You can try all the formulas, but in the end it comes down to experience.”
For his part, Vitale disagrees with installers “who think that putting a commercial downspout on a residential gutter will enable it to hold more water. But the hole on the eave tube can only be so big. So it’s not as effective and it costs more money. After all, you can only put a certain amount of water through a straw.”
But if bigger downspouts aren’t always the answer, then what? “We installed a gutter system for a golf course facility that had tremendous roof areas, with multiple roofs coming down in the same point,” Vitale relates. “Rather than waste money on putting the larger gutters around the entire building, we used a commercial-size gutter for the front and back of the building and residential-size gutters on the sides.”
And in one extreme case of unique architecture, Vitale has even “done a commercial gutter with residential downspouts, because of the way the building was constructed.”
In addition to considering the architecture of a structure, Vitale advises installers to keep in mind the rainfall in their respective markets. “Before sacrificing the look of a home by installing a gutter that seems twice the size of the 5-inch style,” he notes, “ask yourself, ‘Am I in an area like Florida that regularly gets downpours? Or in an area like the Northeast which might get one or two torrential rainstorms per a year?’”
Though Vitale keeps an open mind for each job, he contends, “About the only time you would probably install a commercial gutter on a residential project is if there’s a double vent on the roof. If the roof drip-edge sticks out too far, so that it won’t catch a 5-inch gutter, then you have to use the commercial size. And sometimes the way the valley is formed means you’ll have shingles that hang far out from the fascia board, so a residential-size gutter might not catch the water.”
On any project, Vitale believes it is good practice to fasten gutters every foot instead of the standard 3 feet. As an additional precaution he emphasizes the importance of splash guards. “For any type of valley,” he states, “we put a deflector at least a foot in each direction in the valley. That way, the water will properly displace into the gutter. If we didn’t, any residential roof with a good-size valley would need a commercial-size gutter.”
Manufacturer’s recommendations
As a manufacturer of commercial gutters for the Southeast, Viking Metal Products are made to order. “One of the issues we have in the South is gutters getting clogged by pine cones,” explains Craig. “We want to make sure that not only the gutters are big enough, but the downspouts are an adequate size for everything to flow through.”
Craig says the function must at times be balanced with form. “There are times when you have buildings where aesthetics must be considered,” he relates. “So I’ve seen K-style gutters put on the front of a commercial project, and then standard 8-inch box gutters on the back. The customer wanted K-style on the front to coordinate with the cornice work.”
Another example for the customized needs of commercial jobs, continues Craig, is the need to coordinate roof drainage with any underground drainage system. “If an underground drain system has already been installed,” he explains, “you must customize the downspouts for the drain holes, rather than just letting the water flow into the grass.”
In some cases, Craig acknowledges, commercial-sized gutters may be appropriate for residential jobs. “Valleys will affect the size of the gutter,” he relates. “Steep valleys might mean that the water could jump or run over a residential-sized gutter. I know of spec homes where 6-inch gutters were the best choice.”
For many companies, the size of gutter they install — and the projects they pursue — are driven by the size of gutter machine they own. Many newcomers begin with a 5-inch machine that covers most residential projects. But taking your business to the next level — where custom home jobs and light commercial projects beckon with high profit margins — may require the ability to install larger gutters or a combination of sizes and styles.
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