We will examine two types of wall flashing – head and step flashing.
The first is head flashing:
It is nailed to the wall and then down on top of the shingles.
The top edge should be nailed into the mortar joint and sealed with a polyurethane and the nail heads along the bottom edge as well.
The second type we will discuss more in depth, called step flashing.
Here is a picture of two pieces:
Step flashing is used along a wall when the wall is perpendicular to the roof. An example would be along a dormer window with vinyl siding as shown here:
Below the step flashing pieces at the bottom of the valley, there is a much larger piece of step flashing that I call a pan. It is bigger so that it can handle a greater volume of water, snow, ice, etc. that can build up around the corner.
Below is another picture of a step flashed corner that leaks because the shingles were laid on top of the flashing instead of weaving the shingles into the flashing. Other problems with this area that leaks is that there was no pan flashing around the corner and the wall vent (under the caulking gun) was depending on tar to keep water out.
As you can see the knife below slides up under the step flashing, the shingle under it does not go up under the step flashing leaving an exposed edge across the top of the shingle that water can travel across and get under the shingle and into the house.
Now this is the way it should weave together so that when it rains, the water will run down the wall siding and onto the step flashing and continue running on top of the shingles .
Here I am sliding the next piece of shingle into the flashing just to illustrate. I usually put the shingle tab in first then slide the flashing on top.
Backing up a little bit to the bottom of the valley, here is where a metal pan should be installed to carry excess water around the corner.
And here is a logical progression to the step flashing that has already been shown above.
The brown wall vent has been cut back away from the downspout to prevent water from trying to enter though the end of it. The end has been plugged and sealed to prevent wind driven rain from causing a leak inside.
Here are a few more images which identify water stains due to improper step flashing techniques. Note the orange stain from the tanic acid from leaves which will sometimes show up after leaking has occurred.
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