It’s important to make sure your gutters are large enough to handle the rainfall. If your gutters are too small, rainwater could overflow and damage your exterior or even back up and damage your interior. In most cases, standard five-inch K-style or 6-inch half-round gutters should be large enough to divert water to the drains. 

Keep in mind there’s no such thing as a one-size-fits-all approach in home improvement projects, and gutter replacement projects are no exception. That’s why standard-size gutters might not be large enough for your home. 

Thompson Roofing and Construction, your trusted roofing and siding contractor, shows you how to calculate the correct gutter size below: 

Measure Your Roof’s Watershed Area and Square Footage

The watershed area refers to the area from which water will run off while your roof’s square footage is calculated by multiplying its length by its width. 

Find Out the Rainfall Intensity in Your Area

You can visit the Weather Bureau’s website to find out how much rainfall your area receives. Rainfall intensity is measured in 5-minute intervals and translated to inches per hour. 

Calculate Your Gutter’s Drainage Capacity

Divide your roof’s inch-per-hour watershed by your area’s rainfall intensity to find out how much runoff your gutters would need to divert to the drains. You can then ask your local hardware store about the gutter sizes that can handle that amount of runoff. 

What Are the Other Factors You Need to Consider? 

In addition to your area’s climate and rainfall intensity, you need to consider the shape of your gutters (K-style gutters have more capacity than half-round gutters) and your gutter slope (water will overflow if the gutter slope is too sharp and stagnate in sections of your gutter if it’s not steep enough). Given the fact your gutters are your roof’s first line of defense against the elements and that one miscalculation can leave your roof vulnerable to moisture damage, it’s best to let contractors handle the installation of your new gutters. 

Thompson Roofing and Construction has been proudly serving North Alabama, Metro Huntsville the Shoals & Southern Tennessee since 2008. We offer a wide range of professional roofing services, including gutter replacement and new construction services. To get a free estimate, call us at (256) 252-3188 or fill out this form. We serve homeowners in Huntsville as well as the surrounding AL communities.