Toronto winters are harsh, and flat roofs often bear the brunt of extreme conditions. When spring arrives, one of the most common issues building owners face is cracking in the flat roof membrane. These cracks may seem minor at first, but they’re often the early signs of bigger problems. Understanding why flat roofs crack after winter—and how to address them quickly—can help prevent serious water damage.
The most common cause of cracking is the freeze-thaw cycle. During the day, snow and ice melt and create water runoff that can seep into tiny imperfections in the roofing membrane. At night, temperatures drop below freezing, and that water freezes and expands. Over weeks or months, this process widens those imperfections, causing the membrane to split or blister.
Older flat roofs in Toronto are especially at risk. Materials like modified bitumen or aging rubber membranes become brittle with time. After years of exposure to UV rays and cold temperatures, these materials lose elasticity and are less able to flex with changing weather. When ice forms on a rigid surface, it has nowhere to go—so it creates cracks.
Cracking also commonly occurs around flashing and roof penetrations, such as vents, pipes, and skylights. These areas already experience movement due to wind and thermal expansion. When they’re not properly sealed or when the sealant has aged, they become high-risk zones for water intrusion once cracking begins.
One of the dangers of post-winter cracks is that they often go unnoticed. Water may seep into the insulation layer or travel laterally along the roof deck before signs appear inside. If you start seeing stains on ceilings or hear dripping during spring rainstorms, chances are good your roof cracked during the winter.
Immediate inspection is essential. A flat roofing expert can identify surface cracks, test for underlying water damage, and apply patch repairs or full membrane reinforcements depending on the extent of the issue. For small cracks, cold-applied sealants or self-adhering patches can restore watertight protection. More serious cracking may require partial or full membrane replacement.
Spring is also the perfect time for preventative maintenance. A thorough cleaning, inspection of flashing, and clearing of all drains help ensure that water doesn’t get trapped again and worsen cracks. Reinforcing vulnerable areas before the next winter cycle can also reduce the chance of future damage.
Don’t ignore early signs of damage. For trusted flat roof repair Toronto, contact Flat Roof Repair Toronto. Their team provides thorough inspections, efficient flat roof leak repair, and reliable solutions like flat roof edge repair to stop cracks before they spread.
