How to Repair a Leaky Roof: A Markham Homeowner’s Guide

These are the spots that account for the majority of repair calls in York Region:

• Chimney Flashing
  Failed chimney flashing is the most common source of leaks in Markham homes. The typical failure is counter-flashing cut into the brick that has separated as the mortar degraded over time. In a cold climate, this happens faster because water enters the mortar joint, freezes, expands, and pushes the flashing loose through repeated cycles.
  Reseal with polyurethane caulk where metal meets masonry. Chimneys wider than three feet also need a saddle or cricket behind them to prevent meltwater from pooling. Without one, even properly installed flashing will eventually fail.

• Roof Vents and Plumbing Stacks
  Plumbing vent boots and roof vents are common and often overlooked leak points on shingle roofs. A plumbing vent boot is a protective cover, usually made of rubber or plastic, that seals the area where a plumbing vent pipe passes through the roof. The rubber gasket around the pipe degrades after ten to fifteen years of UV exposure and temperature cycling, and a replacement boot is typically a straightforward job for a roofer.
  Cracked seals around vents can cause roof leaks. Square roof vents can also leak when shingles are pushed tight against their lower flange instead of leaving a small drainage gap. One important thing to avoid: caulking or tarring around vents. It traps water, makes the leak worse, and increases repair costs when a professional has to clean up the mess.

• Roof Valleys and Open Field Shingles
  Valleys are the V-shaped channels where two roof slopes meet, and they carry more water than any other part of the roof. Roofing nails placed within ten inches of the valley centre can cause leaks along the joint.
  Open field leaks are less common but can occur when shingles are staggered less than three inches, or when nail placement falls on a shingle joint. Most open field issues are spotted during a professional inspection rather than from the ground.

• Ice Dams Along the Eaves
  Ice dams are the roof leak source that no American or BC competitor bothers to mention, but they’re one of the most common causes of water damage in Markham homes. Here’s how they form: snow accumulates on your roof, heat from the living space warms the upper section of the roof deck, and the snow melts. That meltwater runs down toward the cold eaves, refreezes, and builds into a ridge of ice. Water backs up behind that ridge and works its way under the shingles.
  The leak often appears as a ceiling stain in an upstairs room during or just after a warm spell in January or February, or after heavy rain, not during the snowfall itself. Markham’s position between Lake Ontario and Lake Simcoe means more lake-effect snow than most of the GTA, combined with frequent brief warm spells that trigger this melt-and-refreeze cycle repeatedly through the winter.
  For a temporary fix, lay a tube sock filled with calcium chloride perpendicular to the ice dam. It melts a drainage channel and lets the water escape. Do not use rock salt; it damages shingles and masonry. The permanent fix is improving attic insulation and ventilation so the roof deck stays cold and snow doesn’t melt on it in the first place. Read more about ice dam formation and how to prevent it.

• Blocked Gutters and Roof Edges
  Clogged eavestroughs push overflow water back under the roof edge, especially during heavy fall rains and spring snowmelt. The resulting leak often appears at the ceiling-wall junction in a room directly below the eaves.
  Clear your eavestroughs in late October after the maples and oaks have dropped, and again in spring after the ice clears. Eavestroughs over twenty years old that are sagging or separating at the seams are worth replacing before they cause ongoing roof edge damage. For more on how this plays out, see our piece on roof problems that often start with eavestroughs.