Why do my gutters leak at the corners?
Why corners specifically
"Seamless" describes the long runs — they're roll-formed as one continuous piece, which is exactly why they don't leak in the middle. But the runs still have to turn corners, and a corner is two pieces of aluminum joined and sealed. So on a seamless system, the miters and the downspout outlets are essentially the only places a leak can start. That's not a defect; it's just where the system's weak points live.
Aluminum moves a lot with temperature. A long run expands and contracts through every NJ day-night cycle and every season, and that movement has to go somewhere. It goes into the corners.
The four causes, in order
| Cause | Tell | Fix |
|---|---|---|
| Old sealant failed | Visible crack or gap in the caulk bead | Strip & reseal properly |
| Debris packed in the corner | Wet leaf pack sitting in the miter | Clean; consider guards |
| Joint pulled apart | Gap you can see daylight through | Re-fasten & reseal, or replace miter |
| Corrosion at the seam | White powder / pitting on aluminum | Replace the corner |
How to reseal it so it actually holds
1. Clean it out completely — debris, grit, all of it. 2. Scrape every trace of the old sealant. This is the step people skip and it's the step that matters: new sealant does not bond to old cured sealant. It bonds to the caulk, the caulk is already failing, and you're back on the ladder next spring. 3. Dry it fully — a wire brush and a rag, and give it time. 4. Seal from the inside of the gutter, working the bead into the joint rather than smearing it over the top. 5. Let it cure before the next rain.
Use the right sealant
Gutter-grade tripolymer or butyl sealant — it stays flexible through freeze-thaw, which is the entire job description. Standard silicone doesn't bond well to aluminum. General-purpose caulk goes brittle and cracks in the first NJ winter. This is a $12 decision that determines whether the repair lasts one season or ten.
When to stop resealing
Once is maintenance. Twice is fine. The third time means something structural is wrong — the joint is working loose, the run is moving because hangers are failing, or the metal is corroding. At that point you're paying $200 repeatedly to avoid fixing the actual cause. Replace the corner, or the run.
The one that isn't a corner problem
If water appears at the corner but the miter looks fine, check whether it's actually coming from behind the gutter — a roof valley dumping concentrated water into that corner, or a missing drip edge letting water curl backward. Inside corners under valleys take an enormous volume of water and often need a splash guard, not sealant. See why gutters overflow and gutter apron vs drip edge.
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FAQ
Why do gutters leak at the corners?
Corners (miters) are a joined seam even on seamless gutters, so they carry all the stress of thermal expansion and contraction. Over time the sealant hardens, cracks, and separates. Debris also collects in corners, holding water against the joint and accelerating the failure.
How do you fix a leaking gutter corner?
Clean the corner completely, scrape out all the old sealant, dry it fully, then apply a gutter-grade sealant to the inside of the joint. Patching new caulk over old failed caulk is the most common mistake and it will fail again within a season.
What sealant should I use on gutters?
Use a sealant made for gutters — a tripolymer or butyl gutter sealant that stays flexible through freeze-thaw cycles. Standard silicone does not bond well to aluminum and general-purpose caulk goes brittle and cracks in a New Jersey winter.
Should I reseal or replace a leaking corner?
Reseal if the metal is sound and the miter is still tight — that is a $150 to $300 job. Replace the corner if the metal is corroded, the joint has pulled apart, or you have resealed it more than twice already.
Related: Repair vs replace · Seamless vs sectional · Why gutters overflow