What is one of the characteristics of top lap in roofing?

The characteristic of top lap in roofing is defined by the fact that it involves shingles being positioned in such a way that at least two layers of shingles overlap each other. This overlapping configuration is crucial for ensuring that water runs off the surface efficiently and does not seep through to the underlying layers. The top lap creates a barrier against weather elements, enhancing the roof's resistance to water infiltration.

This concept is vital for proper roofing installation, as it helps to maintain the integrity and longevity of the roof by preventing leaks and protecting the materials from the elements. The layering of shingles in this manner also contributes to the visual appeal of the roof, providing a consistent and professional look.

Other options present characteristics or definitions that do not accurately describe top lap. For instance, specifying three layers thick would not accurately represent the minimum overlap required, while referring to the slope pertains more to roof design rather than the layering of materials. The mention of exposed areas does not align with the concept of top lap, which is about the interaction between overlapping layers.