Gutter and downspout sizes for Austin rain

5-inch or 6-inch gutters

Angi’s gutter size guide (updated July 2026) says 5 inches is standard for K-style and half-round gutters and recommends 6-inch gutters for areas with heavy rainfall. The same guide says roof square footage, pitch, shape, and local rainfall intensity decide the size, and even small, steep roofs benefit from 6-inch gutters. HomeGuide’s installation guide (dated October 2025) says most homes use 5-inch K-style gutters and that 6-inch gutters for heavy rainfall or large roofs add $1 to $2 per linear foot.

The same Angi guide gives a rule of thumb by roof area for each gutter profile. It doesn’t adjust for rainfall intensity, so read it alongside Austin’s rainfall figures.

How hard it rains in Austin

Gutters are sized against the hardest short bursts of rain. Angi says the National Weather Service measures a region’s maximum rainfall intensity in inches per hour over a 5-minute sample.

NOAA Atlas 14 (Volume 11, Version 2) gives Austin a 5-minute intensity of 6.30 inches per hour for a storm expected every 2 years, 9.58 for a 10-year storm, and 15.4 for a 100-year storm. The same data gives 1.97, 2.99, and 4.79 inches per hour over 60 minutes for the same storms. NOAA says it won’t publish final estimates for its next atlas, Atlas 15, before September 2027, so Atlas 14 is the current reference.

Downspout size and spacing

Angi’s gutter size guide (updated July 2026) pairs 5-inch gutters with 2-by-3-inch downspouts and 6-inch gutters with 3-by-4-inch downspouts. The same guide says to plan one downspout for every 25 to 35 linear feet of gutter, with 40 feet as the maximum between downspouts. HomeGuide’s downspout guide (dated November 2025) says most homes need 4 to 5 downspouts, or one every 30 to 40 feet.

Signs your gutters are too small

Angi (July 2026) says water spilling over the side of gutters during storms, even after cleaning, is a sign they’re too small. The same guide also points to standing water in the gutters, especially near the downspouts. HomeGuide (October 2025) says undersized gutters overflow during heavy rain. If yours overflow, ask us about gutter repair or installation.

Where downspouts can drain

Section R801.3 of the 2021 International Residential Code addresses roof drainage from dwellings. It says, “In areas where expansive soils or collapsible soils are known to exist, all dwellings shall have a controlled method of water disposal from roofs that will collect and discharge roof drainage to the ground surface not less than 5 feet (1524 mm) from foundation walls or to an approved drainage system.”

Texas Water Code section 11.086 says no person may divert or impound the natural flow of surface water in a way that damages the property of another by overflow, and the injured owner may recover damages. HomeGuide’s downspout guide (dated November 2025) says downspouts should extend 4 to 6 feet where the land slopes away from the foundation, and up to 10 feet on flat or sandy soil.