Downspout Installation & Roof Drainage

A gutter only collects water – the downspouts decide where it goes. Too few downspouts, or downspouts that dump water right next to the house, are among the most common causes of overflowing gutters, eroded flower beds and wet basements and crawl spaces.

Downspout basics

• A common rule of thumb is one downspout for every 30 to 40 feet of gutter, more on steep roofs and in heavy-rain regions
• 2x3-inch downspouts are standard on 5-inch gutters; 3x4-inch downspouts carry much more water
• Extensions or splash blocks should move water several feet away from the foundation
• Underground drain lines can carry water to a safe discharge point in the yard

Typical costs

Item	Typical range*
Downspout, installed (per linear foot)	$5 – $16
Downspout, installed (each)	$50 – $240
Upgrade to oversized 6-inch gutter (per foot)	+$3 – $5

*General US ranges compiled from 2026 cost guides (Angi, HomeGuide, This Old House), for orientation only. Local installers set their own prices.

Common drainage mistakes

• Downspouts that end right at the foundation wall
• Upper-roof downspouts dumping onto a lower roof without a diverter
• Long gutter runs with a single downspout at one end
• Buried drain pipes that are crushed or clogged and back up into the gutter

When you get connected, mention any water problems around your home. The installer can plan downspout locations and extensions as part of your new gutter system.

How many downspouts a house needs

Each downspout drains a certain area of roof. Long runs, steep roofs, roof valleys and heavy-rain regions all call for more or larger downspouts. A common sign of too few downspouts is overflow in the middle of a long run or at an inside corner during heavy rain, even when the gutter is clean. Adding a downspout or upgrading from 2x3-inch to 3x4-inch often solves it. See downspout size and placement.

Where the water should go

Downspouts should discharge several feet from the foundation onto ground that slopes away from the house. They should not empty next to window wells, onto walks and driveways where water freezes, onto a septic drainfield or toward a private well. Extensions, splash blocks and buried lines each have a place depending on the yard. See downspouts and your foundation, gutters and window wells and downspouts and icy walkways.

Buried lines, emitters and dry wells

Buried lines carry water underground to a pop-up emitter, a dry well or a curb outlet where allowed. They keep yards tidy but need a steady slope so they drain completely and do not freeze, a cleanout or strainer to stop debris, and a discharge point that will not flood a neighbor. Some cities restrict connections to storm sewers. See underground downspout drainage and downspout disconnection programs.

Downspouts from upper roofs

On two-story homes, a downspout from the upper roof often empties onto a lower roof. That concentrates water on a few shingles and can overload the lower gutter. Extending the downspout into the lower gutter, running it to the ground or adding a spreader protects the roof. See upper-roof downspouts onto lower roofs.

Strainers and clog-prone spots

Elbows and outlets are where downspouts clog. Strainers at the outlets stop leaves and seeds before they enter the downspout, and a cleanout near the bottom makes clogs easier to clear. See downspout strainers and leaf catchers.

Related guides

• Downspout extensions: types, lengths and local rules
• Gutters and window wells
• Downspouts and icy walkways
• Gutters on rural homes: wells and septic
• Upper-roof downspouts onto lower roofs
• Downspout strainers, leaf catchers and cleanouts
• Gutters and landscaping
• Underground downspout drainage
• Gutters in sinkhole country
• Wet basement? Check your gutters first
• Noisy gutters and dripping downspouts
• Gutters and pests: mosquitoes, termites, wasps
• Gutters and scuppers for flat and low-slope roofs
• Gutters overflowing in heavy rain? Causes and fixes
• Downspout size and placement: 2x3 or 3x4?
• Rainwater harvesting from your gutters
• Rain chains vs. downspouts
• Disconnecting downspouts from the sewer: city programs
• Downspouts and your foundation