What is step flashing used for in roofing?

Step flashing is specifically designed to create a watertight seal where the roof meets a vertical surface, such as walls, chimneys, or dormers. It is typically installed in a series of overlapping pieces that are placed in conjunction with shingles, ensuring that water flows away from the penetration and does not cause leaks. This method is highly effective in preventing water from seeping behind the roofing material, which can lead to significant water damage and deterioration over time.

The other options do not accurately describe the primary function of step flashing. While shingles do need to be secured in place, that role is typically fulfilled by nails or adhesive, not step flashing. A decorative edge is not its purpose; flashings are functional rather than aesthetic components of roofing. Lastly, step flashing does not provide insulation, as its role is entirely focused on waterproofing rather than thermal properties.