There are several potential reasons why a roof may only leak sometimes. Some common causes include:

1. Clogged gutters: If the gutters on a roof are clogged with debris such as leaves, twigs, and branches, water may not be able to drain properly. This can cause water to accumulate on the roof, leading to leaks when the water is able to find a way through the roofing material.
2. Damaged or missing shingles: If a roof has damaged or missing shingles, it may only leak when the damaged area is exposed to water. For example, a roof with a missing shingle may only leak when it rains heavily or when snow melts and runs off the roof.
3. Poorly sealed flashing: Flashing is a thin strip of metal or other material that is used to seal the joints between the roof and other structures such as chimneys and skylights. If the flashing is not properly sealed, water may be able to find its way through the joints and cause leaks.
4. Ice damming: In cold climates, ice damming can occur when snow on the roof melts and refreezes at the edges of the roof. This can create a dam that prevents water from draining off the roof, leading to leaks when the water is able to find its way through the roofing material.

To fix a roof that only leaks sometimes, it is important to identify and address the underlying cause of the leaks. This may involve cleaning the gutters, repairing or replacing damaged or missing shingles, resealing flashing, or addressing ice damming.

In summary, a roof that only leaks sometimes