This tool visualizes the most complex part of a metal roof install: the “Water-Shedding Stack.” It specifically addresses the critical layering order (shingle fashion) required to prevent leaks.
It features a “Rain Simulator” that allows users to toggle layers on and off to see exactly how water gets trapped if the Head Flashing is installed on top of the roof panels (wrong) instead of underneath them (correct).
Skylight Flashing Guide
The “Over-Under” Rule for Metal Roofs.
Installation Steps
The Golden Rule: Think Like Water
Always layer materials so the upper piece overlaps the lower piece.
Head Flashing: Must go UNDER the top roof panel.
Bottom Apron: Must go OVER the bottom roof panel.
If you reverse this, water runs under the metal and rots your deck.
Do not rely on caulk to stop water. Caulk dries, cracks, and fails within 2-5 years. Mechanical Flashing (using overlapping metal) lasts 50 years. Use butyl tape sealant only as a gasket between compressed layers, never as the primary exposed seal.