The answer to 'why is my architectural shingles sagging' is that it is likely due to improper installation or underlying structural issues. Architectural shingles are designed to lay flat, but can begin to sag over time due to factors like inadequate roof deck support, poor ventilation, or the weight of the shingles themselves.
Some common causes of sagging architectural shingles include: insufficient nailing during installation, water damage or rot in the roof deck, inadequate attic ventilation leading to heat buildup, and shingles that are too heavy for the roof structure. Sagging shingles can also be a sign of more serious issues like structural damage or foundation problems.