Homeowner note

5-Inch or 6-Inch Gutters?

Fifty inches of rain a year, much of it in summer storms. A worked example of when the bigger gutter earns its cost.

Most houses get 5-inch K-style gutters by default. The question of whether to step up to 6-inch comes down to how much roof drains into each run and how hard it rains. Around Marietta, the second part is easy to answer: Atlanta averages 50.43 inches of rain a year, and July — the wettest month at 4.75 inches — is also the peak of thunderstorm season, when a lot of rain arrives in a short time.

What the guidance says

The federal Building America Solution Center (DOE/PNNL) keeps it simple: gutters come in 4-, 5- and 6-inch sizes, and a larger size conducts more water at a faster rate, provided there are enough downspouts to drain it. Downspouts are sized at about 1 square inch of opening for every 100 square feet of roof, spaced 20 to 50 feet apart.

A worked example

Take a two-story colonial typical of East Cobb, with a rear roof plane 50 feet long and 22 feet from eave to ridge:

Roof area here is the horizontal footprint of the roof plane; steep roofs catch more wind-driven rain. Downspout rule from the Building America Solution Center.
Step	Calculation	Result
Roof area draining to the rear gutter	50 ft × 22 ft	1,100 sq ft
Downspout opening needed (1 sq in per 100 sq ft)	1,100 ÷ 100	11 sq in
A standard 2×3-inch downspout	2 × 3	6 sq in each
A larger 3×4-inch downspout	3 × 4	12 sq in each
Downspouts needed	2 × (2×3) or 1 × (3×4); 50-ft run allows 2	Two 2×3s at the ends, or 3×4s

A 50-foot run with two downspouts and 1,100 square feet of roof is at the point where a 5-inch gutter starts to struggle in a hard July storm, especially if a valley dumps extra water into one spot. Stepping up to a 6-inch gutter with 3×4-inch downspouts gives that run real headroom.

When 6-inch is worth it

Large or steep roof planes, common on two-story homes.
Valleys that concentrate water into one section of gutter.
Long runs where adding downspouts isn't practical.
Roofs that overflow in storms even right after a cleaning.
Homes adding guards, since a wider gutter takes heavy flow better under a cover.

When 5-inch is fine

Single-story ranches with low, short roof planes.
Runs with enough downspouts that already handle storms without spilling.
Historic homes where a bigger profile would look out of scale (see the historic districts note).

What the upgrade costs

Six-inch gutters add about $1 to $2 per linear foot over 5-inch, and the larger downspouts that go with them cost a little more than standard. On the 50-foot run above, that's roughly $50 to $100 — small next to the cost of overflow soaking a fascia board or a foundation. Full price ranges are on the gutter cost page.