The Complete Handbook of Roofing Shingles & Tiles

Chapter 1: Understanding Roofing Shingles & Tiles

A roof is a piece of building physics that most people never think about until it stops working. The shingle or tile you see from the curb is the visible portion of a layered system engineered to do one primary job: shed water off the building envelope while protecting everything beneath it from sun, wind, and thermal stress. To understand what a shingle or tile actually is, you must first understand that the individual unit is a disposable component of a larger, more permanent assembly. A three-tab asphalt shingle is not a roof; it is a sacrificial skin on a structure that includes the roof deck, the underlayment, the flashing, and the ventilation. When one of those other elements fails, the shingle rarely has a chance to do its job, and it will take the blame anyway.

Roofing shingles and tiles are distinguished from other roofing materials, like standing seam metal or single-ply membrane, by their geometry. They are individual, overlapping units installed in a shingle fashion, meaning each course overlaps the course beneath it by a specific amount. This overlapping pattern is the core mechanism of the roof's water-shedding ability. Water runs down the slope and is shed onto the overlapping surface of the next unit below, moving laterally and down off the roof edge. In most climates, this system works perfectly well without being completely watertight on the nail lines, because gravity and the lapping pattern hold the water on the