Short Answer
A skylight integrates with the roofing system through a flashing system that directs water around the skylight opening and over the surrounding shingles. The flashing must be properly layered with the underlayment and shingles — sill flashing at the bottom, step flashing on the sides, and head flashing at the top — so water sheds over and around the skylight without entering. Improper integration is the most common cause of skylight leaks.
Detailed Explanation
A skylight is a penetration through the roof surface, and like all penetrations, it requires a flashing system to manage water. The integration between the skylight and the roofing system involves several layers: the underlayment must be properly installed around the skylight opening, with the underlayment lapped so water sheds away from the opening. The skylight flashing — typically a manufacturer-specific flashing kit designed for the roofing material — must be installed in the correct sequence: sill flashing first (at the bottom of the opening, to catch and direct any water that reaches the skylight), then side or step flashing (on the sides, lapped over the shingles), then head flashing (at the top, lapped over the side flashing and under the shingles above). Each layer must be properly lapped over the one below so water sheds downward and away from the opening. The shingles around the skylight must be properly cut and installed to integrate with the flashing. If any of these layers is installed in the wrong order, if the flashing is damaged or deteriorated, or if the wrong flashing kit is used for the roofing material, water can enter at the skylight. This is why skylight leaks are common and why proper installation — especially during a roof replacement when the flashing can be properly integrated with the new roofing — is critical. A VELUX Certified Installer is trained in the correct installation methods for VELUX flashing systems.
Why It Matters
Proper skylight-to-roof integration prevents leaks. Improper integration is the most common cause of skylight leaks, which can cause significant interior damage.
Questions to Ask Your Contractor
- ?How will the skylight flashing integrate with my new roof?
- ?What flashing kit will be used?
- ?Will the underlayment be properly lapped around the skylight?
- ?Are you trained in the installation of this skylight's flashing system?