Leak at one elbow joint
Water drips or sprays from the seam where an elbow meets the vertical downspout or extension.
Start here: Check for a loose connection, missing fasteners, or a cracked elbow before looking farther up.
Outdoor drainage
Downspout Seam Leaking
Direct answer: A downspout seam usually leaks for one of three reasons: the joint has opened up, water is backing up and forcing out at the seam, or the metal or vinyl has split near the connection. Start by checking whether the seam leaks only in heavy rain or leaks any time water runs through it.
Most likely: The most common fix is a loose or separated downspout connection, especially at an elbow or connector where screws loosen, the section shifts, or old sealant has failed.
Watch the leak pattern before you touch anything. A seam that drips lightly all along one joint points to a bad connection. A seam that gushes during storms usually means water is stacking up above that spot. Reality check: a little seam drip in a hard downpour can still mean a bigger clog or pitch problem upstream. Common wrong move: wrapping the outside with tape without checking for a blockage first.
Don’t start with: Do not start by smearing caulk over a wet, dirty seam. If the downspout is backing up or the joint is pulled apart, sealant alone will not hold for long.
Leaks only in heavy rainSuspect a clog, buried outlet restriction, or overflow from above before blaming the seam itself.
Leaks in a steady hose test at one jointLook for a loose downspout connector, shifted elbow, or cracked downspout section at that exact seam.
Last reviewed: 2026-04-05
What the leak pattern is telling you
Leak only during heavy storms
The seam stays dry in light rain but gushes when the roof is shedding a lot of water.
Start here: Look for a clog or restriction above or below that point, especially at the buried outlet or lower extension.
Leak along a vertical seam
Water beads or runs down the side seam of one downspout section instead of just at a joint.
Start here: Inspect for a split downspout section, freeze damage, or a crushed area that opened the seam.
Leak near the bottom connection
Water spills from the lower seam where the downspout meets an extension or drain adapter.
Start here: Check whether the extension or buried line is blocked and forcing water back up into the joint.
Most likely causes
1. Loose or separated downspout joint
This is the most common cause when the leak is concentrated at one seam and the rest of the downspout looks normal.
Quick check: Grab the lower section and gently wiggle it. If the joint shifts, gaps open, or screws are missing, the connection needs to be reset.
2. Clog or restriction causing backup
When water is forced out of a seam during hard rain, the seam may just be the first weak spot in a backed-up run.
Quick check: Look for water standing in the gutter, spilling at the top, or draining slowly through a hose test.
3. Cracked downspout elbow or split downspout section
A crack usually leaks in the same spot every time, even with a moderate hose flow, and often shows staining below it.
Quick check: Dry the area, then run a hose from above. If water appears through the body of the piece instead of the overlap, the part is damaged.
4. Poor alignment or support strain
If the downspout is twisted, pulled away from the wall, or hanging on one strap, the seam can open up under water load.
Quick check: Sight down the run for bowing, twisting, or a section that no longer nests fully into the next piece.
Step-by-step fix
Step 1: Pinpoint the exact seam and when it leaks
You want to separate a bad joint from a backup problem before you start taking sections apart.
- Wait until the downspout is dry, or wipe the area dry with a rag.
- Look for staining, dirt tracks, or mineral marks that show the true leak point.
- Note whether the leak is at an elbow, a straight connector, a vertical seam, or the bottom outlet area.
- If rain is not available, run a garden hose into the gutter or top of the downspout with a moderate flow and watch the seam.
Next move: If you can clearly identify one seam or one damaged piece, move to the next step and inspect that area closely. If water seems to appear from several places at once, assume there may be a backup above and check flow before sealing anything.
What to conclude: A single repeat leak point usually means a failed connection or cracked part. Multiple wet seams during heavy flow usually point to restriction or overflow pressure.
Stop if:
- The downspout is high enough that you would need to overreach from a ladder.
- The wall behind the downspout is soft, rotten, or actively taking on water.
- The gutter above is pulling loose or sagging.
Step 2: Check for backup above and below the leak
A seam often leaks because water cannot get through fast enough, not because the seam itself is the root problem.
- Watch the gutter above while running water. If it fills unusually fast or spills over, the problem may be upstream.
- Listen at the downspout during the hose test. A hollow rush is normal; gurgling and slow drain-down suggest restriction.
- Disconnect the lower extension if it is easy to remove and test again.
- If the downspout feeds a buried line, watch whether water backs up at the bottom connection instead of flowing away.
Next move: If flow improves and the seam leak drops sharply once the lower extension is removed, the restriction is downstream. If the seam still leaks with the lower extension removed and water is flowing freely, focus on the joint or damaged section itself.
What to conclude: A backed-up lower extension or buried outlet can force water out of an otherwise decent seam. A leak that stays put with good flow usually means the local connection has failed.
Step 3: Inspect the joint fit, fasteners, and support
Once backup is ruled out or reduced, the next most likely issue is a joint that has shifted, loosened, or lost support.
- Check whether the upper piece still overlaps properly into the lower piece and is not cocked to one side.
- Look for missing or loose downspout screws at the elbow or connector.
- Check nearby downspout straps for looseness, missing fasteners, or a section hanging away from the wall.
- Gently push the sections back into alignment by hand. Do not force bent metal hard enough to crease it.
Next move: If the joint seats fully and the leak path disappears or shrinks to a light drip, the repair is likely a reset and resecure job. If the joint will not seat, springs back open, or shows a visible crack, the affected elbow, connector, or section should be replaced.
Step 4: Reset the connection or replace the damaged piece
This is the point where a simple reseat can solve the problem, but cracked or misshapen parts need replacement instead of patching.
- If the joint is just loose, separate it enough to clean out packed debris and old loose sealant.
- Re-seat the downspout pieces so the overlap is straight and fully engaged.
- Re-secure the joint with appropriate downspout screws if the original fasteners are missing or loose.
- If the elbow, connector, or straight section is cracked or split, replace that piece rather than trying to bridge the damage with exterior sealant alone.
- Use sealant only as a finishing step on a clean, dry, properly fitted seam when the joint itself is still sound.
Next move: If the seam stays dry or only shows a trace of moisture during a normal hose test, the repair is likely complete. If the same seam still leaks after a proper reset or part replacement, go back to flow restriction and alignment. Something is still loading that joint.
Step 5: Run a full-flow test and finish the drainage path
You want to confirm the seam repair holds under real flow and that water is being carried away from the house.
- Run a stronger hose flow for several minutes from the top and watch the repaired seam, the gutter above, and the outlet below.
- Check that water exits cleanly at the extension end or buried outlet without backing up.
- Reinstall or straighten the lower extension so it sheds water away from the foundation.
- If the seam still leaks only when the buried line is connected, treat that as a drainage blockage problem and address the downstream line next.
A good result: If the seam stays dry and water exits freely away from the house, the repair is done.
If not: If the seam is dry but water still ponds near the house, the downspout may be fixed while the drainage path still needs work.
What to conclude: A successful repair keeps the joint dry and restores full flow away from the foundation. If the seam is no longer the weak spot, any remaining issue is farther downstream.
Replacement Parts
Repair Riot may earn a commission from qualifying purchases, at no extra cost to you.
FAQ
Can I just caulk a leaking downspout seam?
Only if the joint is still tight, clean, dry, and flowing normally. If the seam is open, misaligned, or leaking because of a clog, caulk is just a short-lived patch.
Why does my downspout seam leak only in heavy rain?
That usually points to backup pressure, not just a bad seam. Check for a clogged gutter outlet, blocked lower extension, or buried drain restriction first.
How do I know if the elbow is cracked or the joint is just loose?
Dry the area and run a hose from above. If water comes through the body of the elbow or a visible split, the elbow is cracked. If it leaks right at the overlap and the pieces move, the joint is loose.
Should the upper downspout piece go inside or outside the lower piece?
The pieces should be assembled so water stays directed into the next section without catching an exposed lip. If a joint was assembled backward, it can leak and trap debris more easily.
When is a leaking seam really a buried drain problem?
If the seam leak gets much worse when the buried line is connected, or the bottom of the downspout fills and backs up, the seam is often just the first place the water can escape. The real restriction is downstream.
Do I need to replace the whole downspout if one seam leaks?
Usually no. Most repairs are one loose joint, one cracked elbow, one bad connector, or one unsupported section. Replace only the damaged piece once you know where the leak starts.