Why it happens
Many homes have roofs at more than one level: a second story above a first-floor addition, a garage, a porch or a bay window. The upper roof’s gutter needs a downspout, and the most direct route down often ends on the lower roof. Running the downspout all the way to the ground may mean crossing a lower roof or a wall where it would look awkward or be hard to attach. So installers often let the upper downspout discharge onto the lower roof, which then carries the water to the lower gutter.
What can go wrong
Shingle wear
A downspout concentrates the water from a whole roof section onto a few square inches of shingles. Over years, that stream washes away the protective granules, wears the shingles thin and can lift shingle edges in heavy rain. The result is a worn stripe below the downspout and, eventually, leaks.
Water under shingles
Water hitting the roof at an angle or with force can be driven up under shingle edges, especially on low-slope lower roofs. Water may also run along the roof-to-wall joint, where flashing is vulnerable.
Overflow at the lower gutter
The lower gutter now carries water from both roofs. If it was sized for the lower roof only, or if the upper water lands near an inside corner, it overflows. That is one of the most common causes of overflow at one specific spot. See gutters overflowing in heavy rain and roof valleys and gutter overflow.
Ice in cold climates
In winter, meltwater from the upper roof can refreeze on the colder lower roof and in the lower gutter, building ice. See ice dams and gutters.
The options
1. Extend the downspout to the lower gutter
Instead of ending on the roof, the upper downspout continues down the lower roof (fastened to it with straps or supports) and discharges directly into the lower gutter. That protects the shingles. The lower gutter still carries both flows, so it may need to be larger or have an extra downspout.
2. Run the downspout all the way to the ground
Where the wall allows, the upper downspout runs down past the lower roof, sometimes routed around it, all the way to the ground. That keeps the upper water out of the lower gutter entirely and is often the best solution when the lower gutter is small. It requires a clear path down a wall and careful attachment.
3. Use a diverter or spreader
Where the downspout must end on the lower roof, a diverter or spreader at the bottom spreads the stream across a wider area of shingles, reducing wear. Splash pads or a metal sheet under the outlet also protect shingles. These are good low-cost improvements but do not reduce the load on the lower gutter.
4. Upgrade the lower gutter
If the lower gutter carries both roofs, upgrading it to 6-inch, using 3x4-inch downspouts or adding a downspout near where the upper water lands prevents overflow. See 5-inch vs. 6-inch gutters and downspout size and placement.
Which option fits
- Small upper roof, large lower gutter: a spreader or extended downspout to the lower gutter is usually enough.
- Large upper roof: run the downspout to the ground, or extend it to the lower gutter and upgrade that gutter.
- Low-slope lower roof: avoid discharging onto it; extend to the gutter or ground.
- Metal or tile lower roof: ask how the downspout will be supported without damaging the roofing. See gutters for metal roofs and gutters on tile roofs.
- Cold climate: avoid routes that send meltwater across cold lower roofs where possible.
Signs of a problem
- A visibly worn or discolored stripe of shingles below a downspout.
- Granules collecting in the lower gutter in one spot.
- Overflow at the lower gutter during heavy rain near where the upper water lands.
- Stains on ceilings or walls below the roof-to-wall joint.
- Ice building on the lower roof below the downspout in winter.
Coordinate with roofing
If shingles below a downspout are worn, they may need replacement. That is roofing work, best done together with fixing the downspout. If the roof is being replaced, it is the ideal time to plan downspout routes too. See new roof, new gutters? Roof-to-wall joints should have step flashing and a kick-out flashing at the bottom, which directs water into the gutter instead of down the wall. See siding and gutters together.
Solar panels and dormers
Solar panels on a lower roof complicate downspout routing because water should not run across or under the panels’ wiring. Dormers create small upper roofs that drain onto the main roof. The same principles apply: spread the flow, protect the shingles and size the gutter below for the combined water. See gutters and solar panels.
Guards on the lower gutter
A lower gutter that receives water from an upper roof also receives that roof’s debris: leaves, needles, seeds and shingle granules all wash down the upper downspout and land in one spot. That spot clogs first. If you install gutter guards, make sure the lower gutter’s guard can handle concentrated flow without water shooting over it, and consider a downspout strainer at the upper outlet so debris stays where it can be reached. Where the upper downspout is extended into the lower gutter, the guard needs an opening or a cut-out at that point. Ask the installer how the guard and the downspout will fit together. See are gutter guards worth it? and downspout strainers and leaf catchers.
Questions to ask the installer
- Where will each upper downspout discharge?
- Will it end on the lower roof, in the lower gutter or at the ground?
- If it ends on the roof, what will protect the shingles?
- Is the lower gutter large enough for both roofs?
- How will downspouts be fastened across the lower roof without causing leaks?
The answers belong in the written quote. See how to compare gutter quotes and gutter parts explained.