The answer to 'why is my architectural shingles water stains' is that it is typically caused by poor ventilation, roof leaks, or improper installation. Architectural shingles are made of multiple layers, and if water gets trapped between these layers, it can lead to unsightly water stains. This is often a sign of a more serious underlying issue that needs to be addressed.
If the water stains are localized to a specific area, it may be due to a roof leak or improper flashing around chimneys, vents, or other roof penetrations. Widespread staining across the roof could indicate a ventilation problem, where moisture is building up in the attic and condensing on the underside of the shingles.