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this would work to shed water. Without the flashing in place, water would roll down the vinyl siding and contact the top of the fascia board. It would run along the top until it found a tiny crack and then it might flow behind the fascia. This could cause a leak indoors or start to rot the wood fascia board, the wall sheathing, or other wood indoors.

With the flashing in place, let’s see what happens. The water runs down the siding and at the bottom of the first row of vinyl siding it drips off and contacts the metal flashing as it runs across the top of the fascia board.

The water then runs off the flashing because it can’t go up the flashing as it extends up behind the siding. It rolls off the downturned edge of the flashing on the face of the fascia board on its way to the ground below.

To make sure the flashing works to it’s best ability, the ends of the flashing at each far end of the fascia board should be turned up making a tiny curb. This forces the water to flow off the front of the flashing across the face of the fascia.

Without these tiny end curbs, the water can roll under the end of the flashing, especially in a fierce wind-driven rainstorm. This expert detailing is often not done by rookies or people who haven’t got a grasp of what’s going

on.

Furthermore, because of capillary attraction, the downturned end of the flashing that folds down over the front of the fascia board should have an air space between the flashing and the fascia board. What’s best is that the downturned edge of the flashing actually should kick out away from the fascia board so the water forms into droplets that fall down to the ground.

If the flashing is tight against the face of the fascia board, the capillary attraction of the water can actually pull the water uphill under the flashing and into the back of the fascia board. Never underestimate the power of capillary attraction. It has rotted out many a home.