How can my basement be leaking when the ground is frozen?

During winters in Southern Ontario, the frost line (the depth to which the ground freezes) can extend to 3.5 feet below grade. As the footings of the majority of foundations are typically 6.5 feet below grade, the lowermost 3 feet of soil above the footing and weeping tile never freezes; therefore, water that is present around the base of your foundation remains fluid throughout the year. Statistically, most foundations leak at or near the bottom of the wall, well below the frost line; thus,  hydrostatic pressure is ever present. Furthermore, other leak sources such as the lower tie-rod holes and snap rods are also located well below the frost line and have constant exposure to water pressure on the foundation wall.

This constant exposure of your foundation to hydrostatic pressure, even in the middle of winter, causes you to be vulnerable to basement leaks even when it is not raining and the snow hasn't melted. Fortunately, any type of basement leak, with very few exceptions, can be repaired even during the coldest winter months.