Is It OK for an Upper Downspout to Drain Onto a Lower Roof?
| # | Table of Contents |
|---|---|
| 1 | Why Builders Do It |
| 2 | What It Does to the Lower Roof |
| 3 | The Wall Next to It |
| 4 | Does It Void the Shingle Warranty? |
| 5 | How to Fix It |
| 6 | What to Look For on Your Roof |
| 7 | FAQ |
Why Builders Do It
On two-story homes with a garage, porch or first-floor section below, the upper gutter needs somewhere to drain. Running a downspout down the wall to the ground means crossing the lower roof, so the easy option is to stop the downspout at the lower roof and let it empty there. It is quick, it is cheap, and it looks clean from the street.
The residential building code does not specifically prohibit it. The International Residential Code's roof-drainage section only requires roofs to drain, without saying where an upper downspout may discharge. Shingle manufacturers, though, are clear that they do not want it, and the Asphalt Roofing Manufacturers Association's residential manual, as quoted in Malarkey's bulletin, says: "Never allow water from a downspout to discharge directly onto a roof below."
What It Does to the Lower Roof
A lower roof is designed to shed the rain that falls on it, spread across its whole surface. A downspout concentrates the runoff from an entire upper roof plane onto a strip a few inches wide, often on a section with a lower slope. The manufacturers list the same effects:
- Granule loss. The steady stream washes the protective granules off the shingles. GAF says this can show up in one to two years or less. Bare shingle mat then ages quickly in the Texas sun.
- Streaking and algae. The constantly wetted strip stays damp longer and can grow algae or moss.
- Leaks. In a heavy downpour, the volume can drive water up under shingle laps. Malarkey compares the effect to an ice dam.
- Debris build-up. Leaves and granules from the upper roof collect where the downspout empties.
Central Texas rain tends to arrive in short, intense bursts, which is exactly when a downspout dumps the most water onto one spot.
The Wall Next to It
Downspouts that empty onto a lower roof often land right where that roof meets a second-story wall. Both GAF and Malarkey list sidewall damage among the effects. Water splashing against the siding and running along the roof-to-wall intersection is the same situation that makes kickout flashing so important: if the step flashing and kickout at that junction are missing or undersized, extra water there ends up behind the siding.
So if you see a downspout emptying near a wall, check the siding just above the lower roof and at the bottom of that roofline for swelling, peeling paint or soft spots.
Does It Void the Shingle Warranty?
No, but it can leave you uncovered. GAF's bulletin states that its shingle limited warranty against manufacturing defects stays in effect, but damage from upper roofs draining onto lower roofs "is not GAF's responsibility." Malarkey says the same: the manufacturing-defect warranty remains, but it does not cover damage caused by building design or water backup.
In practice, a worn strip below a downspout is a roofing problem you will be paying for yourself, which is a good reason to fix the drainage before the shingles wear through.
How to Fix It
The manufacturer bulletins describe the options, from best to most basic:
- Route the water to the lower gutter. Extend the downspout across or down the lower roof so it empties directly into the lower gutter instead of onto the shingles. GAF lists this option, and Malarkey calls a trough that channels runoff to a gutter "the optimal solution."
- Take it all the way to the ground. A longer downspout run down the wall, past the lower roof, to grade. GAF lists this first.
- Splash block or diverter as a minimum. Malarkey recommends a splash block under downspouts if water must land on the roof, but treats it as second best.
When the downspout is moved, the shingles in the worn strip should be checked too. If granules are gone and the mat is exposed, those shingles need replacing even after the drainage is fixed. Our gutter installation team can re-route the downspout, and we can look at the roof below it at the same visit.
What to Look For on Your Roof
- A downspout from an upper gutter that stops above a lower roof.
- A lighter or darker streak running down the lower roof from the downspout.
- Granules collecting in the lower gutter right below that strip.
- Dark staining or moss along the wetted line.
- Peeling paint, swelling or stains on the wall where the downspout empties.
- Interior ceiling stains below that part of the lower roof.
If you see two or more of these, the strip below the downspout is worth a closer look before the next storm. If water is already coming inside, see our roof repair service. Related reading: why gutters pull away from the fascia.
Sources: GAF Technical Advisory Bulletin TAB-R-150, "Damage to Shingles from Gutter and Downspout"; Malarkey Roofing Products Technical Bulletin, "Effects on Asphalt Shingles When One Roof Drains Onto Another" (rev. 08/26), quoting the ARMA Residential Asphalt Roofing Manual (2022); International Residential Code R903.4.
Frequently Asked Questions
Is it against code for a downspout to drain onto a lower roof?
The International Residential Code does not specifically prohibit it; its roof-drainage section only requires that roofs drain. Shingle manufacturers and the Asphalt Roofing Manufacturers Association advise against it.
Will it void my shingle warranty?
According to GAF and Malarkey, no. The manufacturing-defect warranty stays in effect, but damage caused by the runoff from an upper roof is not covered.
How long before the shingles show damage?
GAF’s bulletin says granule erosion can be visible in one to two years or less, depending on how much water the upper roof sends down.
Is a splash block enough?
It helps, but manufacturers treat it as a minimum. Carrying the water to the lower gutter or to the ground keeps it off the shingles entirely.
Can the downspout be moved without new gutters?
Usually. Most fixes extend or re-route the existing downspout. New gutter sections are only needed if the lower gutter is too small for the added water or is damaged.
