What are gutters and downspouts, and how should a downspout be set up?
Short answer. Gutters are the troughs along the roof edge that catch rain, and downspouts are the vertical pipes that carry that water from the gutter to the ground. A downspout works well when it is sized for the roof area it drains, assembled so every joint laps downhill, strapped firmly to the wall, and discharging several feet away from the foundation.
The parts of a downspout
- Outlet or drop: the short collar set into a hole cut in the gutter bottom.
- Elbows: angled pieces that carry the downspout from the gutter back to the wall, and at the bottom turn the water away from the house.
- Downspout pipe: usually rectangular, 2 by 3 inch or 3 by 4 inch on homes.
- Straps or brackets that hold the pipe to the wall.
- Extension, splash block or drain connection at the bottom.
Setting one up
- Place it where water collects. Downspouts go at the low ends of runs, near inside corners below valleys, and often at both ends of long runs. A common rule of thumb is a downspout for every 30 to 40 feet of gutter, more under steep or large roof planes.
- Size it to the roof. A 3 by 4 inch downspout has twice the opening area of a 2 by 3 inch one and is the better choice for big roof sections.
- Lap joints downhill. Each upper piece slides inside the piece below, so water cannot escape at the joint.
- Strap it securely at the top, the bottom and along the run so wind and ladders do not knock it loose.
- Discharge away from the house. Use an extension, a splash block, or a solid pipe to daylight. Where expansive soils are known, the residential code requires roof water to be discharged at least 5 feet from the foundation.
A downspout that dumps beside the foundation undoes most of what the gutter accomplished, especially on Georgia's slow-draining clay. See gutter sizing, seamless gutters and guards and roof anatomy explained.