Final answer:
Granular loss and cupping in a 5-year-old fiberglass shingle roof, despite adequate attic insulation and venting, may be due to manufacturing defects, inferior material quality, harsh weather conditions, or accelerated wear and tear from ultraviolet rays and thermal cycling.
Step-by-step explanation:
The question asks for a reasonable explanation as to why a fiberglass shingle roof that is 5 years old is experiencing granular loss and cupping, despite having adequate attic insulation and venting. A plausible reason for this could be a manufacturing defect or subpar quality of the roofing materials. Typically, fiberglass shingles have a lifespan of 20 to 30 years, and significant granular loss and deformation within 5 years is uncommon and could be indicative of a product issue. Another possibility is that the roof has been subjected to harsh weather conditions or mechanical damage which can accelerate wear and tear. The effects of ultraviolet rays and thermal cycling may also degrade the bond between the granules and the asphalt base, leading to early granular loss. Without visual inspection and further information, it is difficult to pinpoint the exact cause, but these are some probable factors contributing to the premature deterioration of the shingles.