When asphalt shingles are installed over existing shingles, where is leakage most likely to occur?

Leakage is most likely to occur at penetrations when asphalt shingles are installed over existing shingles. This is primarily due to the fact that penetrations, such as vents, chimneys, and skylights, are points where the roofing material is interrupted. When new shingles are laid over existing ones, proper flashing and sealing around these penetrations become critical. If the installation is not done correctly or if the existing shingles have deteriorated, water can easily find its way beneath the layers, leading to leaks.

Additionally, penetrations are often complex areas where water can collect and not drain properly if the surface and flashing are not adequately prepared or if there are existing issues with the underlying shingles. This lack of proper sealing creates an increased risk for water intrusion, making it essential for home inspectors to pay close attention to these areas during an inspection, especially when verifying roofing materials.

In contrast, while leakage can occur in other parts of a roof, such as at eaves, ridges, or hips, these areas generally have more straightforward water-shedding designs and might not be as susceptible to prolonged leakage when shingles are layered over existing ones.