When rain falls at one inch per hour, a five-inch K style gutter carries the runoff from roughly 2,500 square feet of roof. We do not size a Naples gutter to one inch per hour. The National Oceanic and Atmospheric Administration puts the hundred year hourly rate here at about 4.6 inches, and at that rate the same trough covers closer to 550 square feet. Both numbers describe the same house and the same trough at two different rain rates. That gap is why a gutter in Naples can handle every ordinary shower and still send water over the lip in a hard one. PRG Roofing & Construction Inc. works out of Fort Myers, and our crew measures a gutter against the rain rate and sizes it from the reading.
How Hard The Rain Falls Sets The Size
We base gutter sizing on the 100 year, one hour rainfall rate for the location, published in the Atlas 14 tables, which is the rate the system is built to carry. The International Plumbing Code storm drainage chapter sets that method for a practical reason, because an annual rainfall total says nothing about the hardest hour of the year. Rain here arrives in short, heavy bursts, and that hardest hour is the one your gutter system has to carry. Clearing a trough restores it to the capacity it was built with, and a gutter that was short on capacity to begin with will still spill in a hard storm. So when a gutter was cleaned recently and spilled again in the next storm, size is one of the first things we check, along with the outlet count, pitch, and discharge point.
The Outlet Count Behind Every Trough Size
A flow test shows two things about a gutter at once, the fall of the trough toward the downspout and the speed the outlet takes water away. On the sizing side, SMACNA rates a five-inch half-round gutter on a level run at roughly 26 gallons per minute, and a six-inch half-round at roughly 40. Moving up one trough size adds about half again as much capacity, not twice as much. The downspouts are the real limit, since a large trough with a single outlet still backs up. We count downspouts against the roof area feeding each gutter.
Why A Seamless Gutter Holds Up At The Joints
A seamless gutter system is formed on site in one continuous length, so the only joints anywhere in the gutter are at the corners and the outlets. A sectional system joins pre-cut lengths and adds a sealed connector every 10 to 20 feet. Sealant, ultraviolet exposure, and daily thermal movement all act on the same spot at every one of those connectors. The inside of a continuous trough is smooth end to end, which gives pine needles, twigs, and shingle granules nothing to catch on before going down the downspout. Heavy litter from oaks, pines, and palms means you should be clearing the gutters and downspouts at least twice a year, and a smooth trough makes that a shorter service call.
The Fascia And Soffit Behind The Trough
Water that overshoots the trough runs down the fascia board and back into the soffit behind it. Persistent moisture at the structure is the conducive condition that University of Florida IFAS Extension and state guidance both name for subterranean termites, and both point to keeping soffits sound and vents screened. A gutter that takes water cleanly off the edge is the first part of keeping that wood dry and sound. Our crew photographs the fascia line on these visits, so the current condition of that wood is documented while the gutter is being measured.
The Last Few Feet Of The System
The last part of the gutter system is the few feet past the bottom of the downspout. Roof runoff released right at the wall line soaks the soil against your home’s foundation and washes out the bed underneath. The standard remedy is straightforward, carrying that discharge three to four feet or more away from the foundation with extensions. We check that distance when we measure the gutter, because a correctly sized gutter still needs somewhere to put the water it collects.
The Pitch Check And The Flow Test On A Measured Visit
On a measured visit our crew sets a laser level along the trough and runs a flow test, so the fall and the outlet speed are both confirmed on the spot. SMACNA sets minimum pitch at 1/16 inch per foot, which comes to 5/8 inch of drop across 10 feet toward the downspout, and that much fall moves water without reading as crooked from the curb. Hangers go no more than 24 inches on center to carry a trough full of water, and we set them to let the aluminum expand and contract with the heat. Those readings, together with the rain rate and the outlet count, set the size of the gutter we build. Call PRG Roofing & Construction Inc. at (239) 237-2906 to have your gutter measured against the rain rate.
