Guides
How to Install Gutter Drainage System: Gutters, Downspouts
How to install gutter drainage system: sizing ranges, quarter-inch fall per 10 feet, hanger spacing, downspout discharge, sealant joints, water-test checks.
What to take away
- Heavy rain capacity comes from gutter width, downspout size, and constant fall.
- Use a roof-area table or your local code before buying parts.
- The step that decides the result is setting a fall of one quarter inch per 10 feet toward the outlet.
- Check each run with a level, then with a garden hose.
- Stop and call a licensed pro if the fascia is soft, the roof edge is over 20 feet high, or the discharge crosses a driveway.
How to install gutter drainage system starts with the roof area and the local storm, not with the gutter hangers. Use a code table or a simple roof-area check before you buy parts. The sections below follow the work in the order a DIY installer should use.
What has to be true before the first step
The fascia board must be sound. Probe it with a screwdriver; dry, firm wood holds hangers. The roof edge must have a drip edge or the gutter back must tuck behind it.
Each downspout outlet must have a place to discharge at least 10 feet from the foundation. A splash block, a buried pipe, or a rain garden all work.
Know the roof area each downspout will serve. Measure the horizontal footprint of the roof section, not the sloped surface. In most US towns the permit office is the local building department, and the model code it adopts is usually the International Residential Code, which sizes roof drainage by rainfall rate and roof area. Ask which edition is in force locally, and whether the work needs a permit and an inspection.
Canadian practice uses metric rainfall rates; Canadian gutter installers size eavestroughs under the National Building Code. This comparison matters if the property is near the border.
Sizing gutters and downspouts for your roof area
A 5-inch K-style gutter with a 2 by 3 inch downspout handles most roof sections up to about 600 square feet. For 600 to 1,200 square feet, a 6-inch K-style gutter with a 3 by 4 inch downspout is safer. These ranges are illustrative; size from the roof-drainage table in the code your local building department has adopted before cutting metal.
Gutter and Downspout Sizing by Roof Area
Up to 600 sq ft
- Gutter size
- 5 inch K-style
- Downspout size
- 2 by 3 inch
600 to 1,200 sq ft
- Gutter size
- 6 inch K-style
- Downspout size
- 3 by 4 inch
Over 1,200 sq ft
- Gutter size
- 6 inch half-round
- Downspout size
- 3 by 4 inch plus second outlet
In a Gulf Coast cloudburst, a 5-inch gutter on a long run can overflow even with correct slope. In the Pacific Northwest, long drizzle exposes sealant leaks. In Minnesota, snowmelt needs clear outlets before spring rain.
Tools and materials for the job
- A tape measure and a string line with a line level.
- A 4-foot level, a cordless drill, and hanger screws.
- Tin snips or a hacksaw for cutting gutter sections and downspouts.
- Gutter sealant, end caps, lap joints, elbows, and gloves.
- The gutter and downspout sizes from the sizing section above, plus hangers for the run.
- Discharge partsa splash block, or pipe with a pop-up emitter, or soil and plants for a dry well or rain garden.
The installation sequence
- Mark the high point at the end farthest from the outlet. Drive a temporary screw into the fascia.
- Tie a string line from that screw to the outlet with a fall of one quarter inch per 10 feet of run.
- Install each hanger so the back of the gutter follows the string. Space hangers no more than 24 inches apart.
- Cut and join gutter sections with lap joints. Overlap each upper piece over the lower piece in the direction of flow.
- Install the outlet and downspout, then run an elbow to the discharge point.
- Seal every joint and end cap with gutter sealant. Wipe the bead smooth with a gloved finger.
- Remove the string and run a water test with a garden hose.
A clean run makes later service easier. The new-hire checklist for a gutter service business lists what a service crew should inspect after installation, including bracket spacing and sealant condition.
Gutter Installation Sequence
- Mark high point, drive temporary screw
- Tie string line with 1/4 inch per 10 feet fall
- Install hangers no more than 24 inches apart
- Cut and join sections with lap joints
- Install outlet and downspout, run elbow
- Seal every joint and end cap
- Remove string and run water test
Installing the discharge
The sequence above ends at the downspout elbow. Carrying the water the rest of the way is a second job, and it takes one of three forms.
- Splash block.Set the block on packed soil that falls away from the house, at least 10 feet from the foundation. The elbow must not touch the block.
- Buried pipe.Dig the trench from the elbow to the outlet with a steady fall away from the house, lay the pipe on a firm, settled base, and end it at a daylight outlet or a pop-up emitter so water leaves the trench. A dip in the trench holds water and freezes.
- Dry well or rain garden.A dry well is a gravel-filled pit that stores roof water until it soaks away. A rain garden is a shallow planted basin with amended soil. Either one belongs at least 10 feet from the foundation, on ground that sheds water away from the house.
Whichever form you use, test it with the hose. Water must leave the foundation area and must not stand in the trench.
The step that decides the result
The fall of the gutter is the step that decides whether heavy rain leaves the roof or spills over the edge. Set a fall of one quarter inch per 10 feet of run, never less. A level gutter may look right but leaves water standing. Too much fall makes water shoot past the outlet.
Gutter Fall: The Deciding Number
1/4 inch per 10 feet
Never less, or water stands
Too much fall shoots past outlet
Midpoint gap: about 1/8 inch
Check the fall with a string line and a small line level. Measure from the string to the gutter back at the midpoint; the gap should be close to one eighth inch on a 10-foot run.
How to check each step came out right
Use a 4-foot level against the gutter back after hanging the first 10-foot section. The bubble should sit just off center in the direction of flow. Run the garden hose from the far end and watch the water path. No water should stand after the hose stops. Every joint should look dry on the outside after the test.
- Gutter back follows the string line at every hanger.
- Water flows to the downspout without pooling at the midpoint.
- Downspout discharge lands at least 10 feet from the foundation.
- Joints show no drips after the water test.
For the final discharge, EPA's Soak Up the Rain guidance describes how to build a rain garden or dry well.
What to do when a step goes wrong
The common failure is a sagging run in the middle. The recovery is to remove the hangers in the sagging section, reset the string line, and rehang the gutter so the back follows the line. Do not keep adding sealant; sealant cannot fix a low spot.
If water backs up at the outlet, the downspout may be too small or the outlet may be clogged. Remove the downspout and check for debris. A buried pipe that holds water may be crushed or pitched backward.
FEMA's building science page explains how standing water near a foundation can cause damage. If local rules require disconnection, compare downspout disconnection rules to see how a disconnection program should work.
When to stop and hand it to a professional
Stop and call a licensed gutter contractor if the fascia board is soft or split when probed. Stop if the roof edge is more than 20 feet above grade; fall protection and ladder work become a different risk.
NIOSH's falls page describes how ladder falls injure homeowners every year. Stop if the downspout must cross a driveway, a sidewalk, or a utility line without a prepared trench.
If the property crosses the US border or you run a crew on both sides, cross-border gutter business explains the licensing and tax differences.
