When adding a second layer of roofing, which issue is a likely concern?

When adding a second layer of roofing, which issue is a likely concern?

• A. The dead load is increased
• B. It reduces the roof height
• C. Roof materials may not dry properly
• D. It improves ventilation

Answer: (C)

The main idea here is how moisture moves in roof assemblies. Adding a second layer makes the roof thicker and tighter, which slows down evaporation and air movement through the roof. That means any moisture present in the old roof deck or underlayment has fewer paths to escape, so it can trap dampness between the layers. Over time, this increases the risk of wood rot, mold, and deterioration of roofing components. This drying issue is the most likely concern when another layer goes on. The added weight from two layers is real and can stress the structure, but the question focuses on what happens to moisture. And while ventilation can be affected, it’s not an improvement—often it’s hindered by the extra material.

The main idea here is how moisture moves in roof assemblies. Adding a second layer makes the roof thicker and tighter, which slows down evaporation and air movement through the roof. That means any moisture present in the old roof deck or underlayment has fewer paths to escape, so it can trap dampness between the layers. Over time, this increases the risk of wood rot, mold, and deterioration of roofing components. This drying issue is the most likely concern when another layer goes on.

The added weight from two layers is real and can stress the structure, but the question focuses on what happens to moisture. And while ventilation can be affected, it’s not an improvement—often it’s hindered by the extra material.