Which practice is common when installing shingles?

Staggering seams when installing shingles is a well-established practice in roofing that serves a crucial functional purpose. By offsetting the seams from one row of shingles to the next, roofers create a more robust barrier against water infiltration. This design minimizes the chance of water running directly down a seam, which could potentially lead to leaks.

When seams are staggered, any water that manages to penetrate the top layer of shingles is less likely to reach the underlying structure, as it has to navigate around multiple layers before it can penetrate deeper. This method enhances the roof's ability to shed water effectively and provides a more durable and reliable roofing system.

The other options do not emphasize essential practices for effective roofing. Aligning seams for aesthetic purposes does not contribute to the roof's performance regarding water resistance. Using a single layer of shingles can compromise durability and insulation. Lastly, applying shingles without any underlayment would expose the roof to water damage risks, as underlayment acts as an important additional layer of protection against moisture.