How do I stop my eavestrough from overflowing at just one specific corner during Ottawa storms?

Overflow at a single corner during heavy rain is one of the most common and fixable eavestrough problems Ottawa homeowners encounter, and the good news is that it almost always comes down to one of three root causes you can diagnose yourself before calling anyone.

Why One Corner Overflows While the Rest of the System Works Fine

The most likely culprit is inadequate slope toward the downspout. Eavestroughs must maintain a minimum drop of one-quarter inch for every 10 feet of run, directing water consistently toward the outlet. If a section has settled, pulled away from the fascia slightly, or was installed with a low point near that corner, water pools there and spills over the front lip during heavy rain. Ottawa's extreme freeze-thaw cycle — 50 or more times per winter — is notorious for shifting hanger positions and creating sags that weren't there when the system was new. Stand on a ladder after a rain and look for standing water sitting in the gutter trough. If you see a puddle between storms, you've found your sag.

The second common cause is a blocked or undersized downspout at that corner. Even a partial blockage from compacted leaves, a maple key nest, or a bird's debris can restrict flow enough that the gutter fills faster than it drains during an Ottawa thunderstorm. Flush the downspout from the top with a garden hose at full pressure. If water backs up rather than flowing freely out the bottom, you have a blockage. A plumber's snake or a strong burst from a pressure washer nozzle usually clears it. Ottawa's mature tree canopy — particularly in neighbourhoods like the Glebe, Westboro, and Old Ottawa South — makes downspout blockages extremely common in fall and spring.

The third possibility is that the drainage area feeding that corner is simply too large for the existing downspout. A single 3-by-4-inch downspout can typically handle about 50 to 70 square feet of roof drainage area in normal rain. Ottawa's intense summer convective storms regularly dump 30 to 50 millimetres of rain per hour, which overwhelms systems that were sized for average rainfall. If your roof has a steep pitch, a large valley, or a dormer that channels extra water toward that corner, you may need an additional downspout installed nearby or an upgrade to a larger 4-by-5-inch downspout.

From a practical standpoint, start your diagnosis on a dry day by checking the gutter slope visually — a long level or a laser level works well for this. Then flush the downspout with a hose. If slope and drainage are both fine, measure the roof area draining to that corner and compare it to your downspout size. A second downspout added 6 to 10 feet from the problem corner costs roughly $200 to $500 installed in Ottawa, and it often solves overflow problems permanently.

One important Ottawa-specific note: if this corner also develops ice buildup in winter, the overflow and the ice dam likely share the same root cause — poor drainage slope creating a standing water zone that freezes solid. Fixing the slope now protects you from both problems.

If your gutter is sagging because hangers have pulled out of the fascia board, check whether the fascia wood itself is soft or rotted. Rotted fascia cannot hold new hangers and needs to be replaced before any eavestrough repair will hold through another Ottawa winter. That moves the project into soffit and fascia territory, which is worth having a professional assess.

For a single-storey home, the flushing and visual inspection steps above are safe DIY work. Re-sloping a section by repositioning hangers is manageable for a handy homeowner on a bungalow. But if the overflow corner is on a two-storey wall, or if you suspect fascia rot, it's worth bringing in a professional. You can browse eavestrough contractors serving Ottawa through the Ottawa Construction Network directory at justynrookcontracting.com — it's a free resource and a good starting point for getting a few quotes.