July 2026 is now the rainiest month Ottawa has recorded since Environment Canada started keeping data in 1873. About 270 mm of rain fell at the Ottawa Airport — well past the old record of 250.2 mm, set in 1899, and past the more recent 249.8 mm record from July 2017. Normal July rainfall here is about 89 mm, so this July brought roughly three times the typical amount, on top of a June that also ran above average. According to retired federal climatologist David Phillips, July’s rain alone represented about 40 per cent of what Ottawa would normally see in a full year.
None of that shows up as a single dramatic event. There was no tornado, no widespread roof-tear-off footage. That’s exactly why it’s worth writing about: sustained, repeated saturation does a different kind of damage than a single storm, and it’s the kind most owners don’t think to check for.
Why prolonged rain is a different problem than a storm
A roof is built to shed water fast, not to sit under it for weeks. When rain falls this consistently, three things happen that a single heavy storm doesn’t cause on its own.
Flat and low-slope roofs pond. Commercial and multi-residential flat roofs are designed to drain, but repeated rain without enough dry time between events lets water sit in low spots longer than it should. Ponding water finds every weak seam, fastener, and flashing detail, and it doesn’t take a single big rainfall to do it — it takes weeks of the roof never fully drying out.
Moisture works its way in slowly. A sloped residential roof in good condition can shed a heavy storm without issue. Repeated saturation is different: water has more opportunities to find a marginal flashing detail, an aging boot, or a seam that would hold up fine against one storm but not against weeks of nearly constant exposure.
Attics and insulation take longer to dry. Persistent humidity and rain slow down how quickly a roof assembly dries between events. A ventilation gap or a compressed insulation area that’s a non-issue in a normal summer becomes a real moisture risk when the roof rarely gets a chance to dry out.
The result is that damage from a month like this often doesn’t appear as a leak in August. It shows up as a stain in October, or a soft spot discovered during a fall inspection — well after anyone connects it back to the rain.
What’s worth checking now
An inspection after a record-wet month isn’t about finding storm damage — it’s about catching slow saturation before it becomes a fall or winter leak. That means checking flat roofs for standing water and drainage performance, confirming flashing and seams are still sealed after weeks of exposure, and checking attic spaces for humidity or early signs of moisture rather than waiting for a ceiling stain to appear.
The throughline
The roofs that come out of a summer like this fine aren’t necessarily the newest ones — they’re the ones that get looked at now, while any moisture damage is still small and dry, instead of in November when it’s neither.
About the Author
Lawson Leblanc is Service Manager at Vanity Roofing, Ottawa’s Exterior Experts. Twenty-two years ago he started on the tools — framing, roofing, siding — and worked his way up to running service for the company, which means he’s the one who gets called when a roof that seemed fine develops a problem months later. That vantage point, seeing installs from the ladder and callbacks from the office, is where most of what’s above comes from. Learn more or book an inspection at vanityroofing.ca.
