Most gutter companies quote one size for the whole house. That is why so many Wasatch Front homes have five-inch gutters on a back eave that drains half the roof and overflows every March. Here is how to decide size the way we do it: run by run.
The Numbers
A five-inch K-style gutter carries about 1.2 gallons per linear foot and handles roughly 5,500 square feet of roof per downspout in a one-inch-per-hour storm. A six-inch gutter carries about 2 gallons per foot, handles roughly 7,900 square feet per downspout and takes a three-by-four downspout instead of two-by-three. That is about forty percent more capacity, and a downspout opening that is far less likely to freeze solid or plug with cottonwood seed.
Why Snow Changes The Math
Rainfall tables assume water arrives at the gutter at the rate it falls. Snowmelt does not work that way. A bench home in Cottonwood Heights or Bountiful can carry two feet of snow on the roof after a storm, and when a south-facing slope lets go on a sunny March afternoon, the gutter gets a season’s worth of water in an hour. The gutter also has to hold the ice that forms along shaded eaves in January, and six-inch profiles in .032 gauge handle that weight better.
Go To Six-Inch When
- The roof pitch is 8/12 or steeper, so water hits the gutter fast and can overshoot five-inch
- One eave collects water from a large or complex roof, or from a valley that concentrates flow
- The home sits on the bench, in a canyon mouth or above about 5,000 feet
- The roof is metal, which sheds water and snow in sheets
- Downspouts freeze or clog every winter
- You already see overflow at the same corners every spring
Five-Inch Is Fine When
- The roof is moderate pitch, under about 2,500 square feet and drains to four or more downspouts
- The home is on the valley floor in Murray, Taylorsville, West Jordan, Orem or west Layton
- The run is a porch, bay window or small section with its own downspout
- You are matching existing five-inch gutters on an addition and the system has never overflowed
Downspouts Matter As Much As Size
One downspout per thirty to forty feet of gutter is the rule. Many builder installs along the Wasatch Front have half that, which is why corners overflow even with correctly sized gutters. Adding a downspout to a five-inch run is often cheaper than upsizing and solves the same problem. A good estimate looks at both.
What Upsizing Costs
Six-inch seamless aluminum runs about $2 per foot more than five-inch, or $300 to $500 on a typical house. Three-by-four downspouts add about $25 each over two-by-three. On a bench home that overflows every spring, it is the cheapest fix available.
Mixing Sizes
Many of our installs are six-inch on the main eaves that carry the most roof and five-inch on porches and small sections. Nobody notices the difference from the street, and it keeps the cost down without giving up capacity where it matters.
See the full comparison on our five-inch vs six-inch page and the gutter types overview.
Ready for a number on your own house? SwiftHand Gutters gives free, itemized estimates across Salt Lake, Utah, Davis, Weber, Summit and Wasatch counties. Request a free estimate or call 801-784-6712.
