5-Inch vs. 6-Inch Gutters: What Size Does Your PNW Home Need?

Most homeowners never think about gutter size until something goes wrong: water pouring over the edge during a storm, a soggy flower bed below a roof valley, or a damp crawl space that shows up every winter. In many cases, the gutters are not clogged or broken. They are simply too small for the amount of water the roof sends them.

Five-inch K-style gutters are the most common size on residential homes, but they are not the right choice for every house. At Red Raven Exteriors, we size every seamless gutter system for the roof it serves. Here is what you need to know.

The Basics: K-Style Gutter Sizes

The size of a gutter refers to its width across the top opening. The two most common residential sizes are:

• 5-inch K-style: The standard on most homes. Suitable for many average-sized roofs with moderate pitch.
• 6-inch K-style: Holds and moves noticeably more water. A 6-inch gutter is commonly cited as carrying roughly 40 percent more water than a 5-inch gutter.

That extra capacity may not sound dramatic, but during a heavy Pacific Northwest downpour, it can be the difference between water flowing into your downspouts and water sheeting over the front of your gutters.

Downspouts Matter Just as Much

A gutter can only drain as fast as its downspouts allow. The two common residential downspout sizes are:

• 2x3-inch downspouts: About 6 square inches of opening. Standard on many homes with 5-inch gutters.
• 3x4-inch downspouts: About 12 square inches of opening, or roughly double the flow area.

Upgrading to 3x4-inch downspouts is one of the most effective ways to improve drainage, even without changing gutter size. Larger downspouts are also much less likely to clog from fir needles and leaf debris, which is a big advantage under Eastside tree canopy. Learn more about our downspout installation service.

What Determines the Right Gutter Size?

Professional gutter sizing considers several factors together.

Roof Drainage Area

Each gutter run collects water from the roof plane above it. A long, uninterrupted roof plane sends far more water into its gutter than a small section over a porch. The larger the area feeding a single run, the more capacity that gutter needs.

Roof Pitch

Steeper roofs shed water faster and concentrate it into the gutter more quickly. Wind-driven rain also strikes more of a steep roof’s surface. Steeper roofs generally benefit from larger gutters.

Rainfall Intensity

Gutters are sized for peak rainfall rates, not annual totals. While Seattle-area rain is often steady and light, fall and winter storms, including atmospheric river events, can deliver intense bursts that overwhelm undersized systems. Our guide to preparing your home for atmospheric river season covers why these storms are so hard on drainage.

Valleys

Roof valleys funnel water from two roof planes into a single point. The gutter directly below a valley often receives a concentrated stream that overshoots or overflows a 5-inch gutter, even when the rest of the system works fine.

Number and Placement of Downspouts

Long gutter runs with only one downspout force water to travel a long way and back up during heavy rain. Adding downspouts can improve performance as much as increasing gutter size.

Tree Cover

Homes under Douglas fir, cedar, and big-leaf maple collect more debris. Larger gutters and downspouts give debris more room to pass through and reduce the chance of a clog causing overflow.

Signs Your Gutters Are Too Small

Watch your gutters during a heavy rain. These are the most common signs of undersizing:

• Water spills over the front edge even when the gutters are clean
• Overflow concentrated at inside corners or below roof valleys
• Erosion lines or splash marks in the soil or mulch below the gutter
• Staining or peeling paint on siding and trim below the gutter line
• Water in the crawl space or basement after big storms
• Downspouts that gush or back up at the top during heavy rain

Before assuming your gutters are undersized, rule out clogs, improper pitch, and sagging sections. Our fall gutter maintenance checklist walks through how to check for these problems.

When to Choose 6-Inch Gutters

Six-inch gutters are often the better choice for:

• Larger homes with long, uninterrupted roof planes
• Steep-pitched roofs
• Roofs with valleys that empty into a single gutter section
• Homes with heavy tree cover and frequent debris
• Metal roofs, which shed water very quickly
• Homes with a history of overflow, foundation moisture, or crawl space water
• Homes where you plan to install gutter guards, since guards can slightly reduce water entry during intense bursts

When 5-Inch Gutters Are Enough

A properly installed 5-inch system with enough downspouts works well for many homes, especially:

• Smaller homes and single-story ramblers with moderate roof pitch
• Roofs with short runs and few or no valleys
• Garages, sheds, and small additions

Five-inch gutters are also slightly less expensive and have a lower profile, which some homeowners prefer visually on smaller homes.

Does Upsizing Cost Much More?

Six-inch seamless gutters cost modestly more per linear foot than 5-inch gutters, and 3x4-inch downspouts cost a bit more than 2x3-inch. For most homes, the difference is a small percentage of the total project cost. Compared with the cost of repairing foundation erosion, rotted fascia, or a wet crawl space, upsizing is usually inexpensive insurance.

If you are replacing gutters anyway, it is the ideal time to make the change. Upsizing later means replacing the entire system.

Don’t Forget Where the Water Goes

Even perfectly sized gutters cannot protect your home if downspouts dump water right next to the foundation. Every downspout should discharge well away from the house, either through extensions or underground drain lines. Our guide to downspout drainage solutions explains the options.

Get Your Gutters Sized Correctly

We measure your roof areas, evaluate pitch and valleys, look at your tree cover and drainage, and recommend the gutter and downspout sizes that will actually handle Pacific Northwest storms.

Contact Red Raven Exteriors for a free gutter assessment, or learn more about our gutter installation and gutter guard services. Visit the Red Raven Exteriors home page to see all of the exterior services we offer across King County, and subscribe to our RSS feed for more practical home maintenance guides.