Where Two Systems Meet

A tile roof and a membrane roof are different systems with different installers, and the transition between them belongs to neither. It is routinely detailed on site rather than designed, and it is the single most common leak location on this kind of roof.

The volume of water makes it worse. A large tile roof sheds everything it collects onto a comparatively small transition detail, so the junction handles far more water per square foot than either roof does. It is the highest-loaded detail on the building and typically the least designed.

The membrane has to run up under the tile and its underlayment far enough that water shedding off the tile lands on the membrane rather than behind it. That means the tile at the junction is lifted, the flashing is set, and the tile is reset over it.

What it does not mean is a bead of sealant where the two surfaces meet. That is the repair almost every leaking transition has already had, usually more than once, and it is why the junction is still leaking.

1. 01Treat the transition as a designed detail, not a site decision.
2. 02Flash and terminate both systems properly at the junction.
3. 03Allow for movement between the two.
4. 04Water test the junction after repair.
5. 05Document the detail for future work.

Water test the transition after repairing it. It is the most common leak location on a mixed roof, sealant-based repairs there fail routinely, and a hose is the only way to know before the next storm does.

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