The inland sun does the slow damage on a Glendale roof
Homeowners are regularly surprised to learn that the hardest thing on their roof is not the rain, it is the sun, and in Glendale that holds especially true because of how warm and dry this inland stretch runs. From late spring well into autumn the city sits under long, cloudless days of strong, high-angle light, and the warmth here pulls well ahead of the coast just a few miles west. A roof soaks all of that up. On a composition roof the ultraviolet steadily strips the volatile oils out of each shingle, the mat stiffens and loses its give, the surface granules let go and wash into the gutters with the first rain of the season, and the edges begin to curl and lift. We meet Glendale shingle roofs constantly that read a full decade older than their true age, simply because the inland sun pushed them harder than any warranty ever planned for.
Tile carries the sun beautifully on its surface, but the layer that decides whether the house stays dry is not the tile, it is the underlayment hidden beneath, and that layer does not escape so lightly. Heat radiates down through the clay or concrete and across the air space onto the felt or synthetic membrane that is doing the actual waterproofing, and decade upon dry decade that paper loses its flexibility and at last cracks. This is the reason a Glendale tile roof can need serious work while the tiles overhead still look proud from the street, and why the only honest way to judge a tile roof in this city is to read the underlayment rather than admire the tile.