Please help me understand why they have to use - step flashing
When they could just use “headwall flashing”
Yes I know they are two different pictures, just wondering why all the little pieces of step flashing vs one long angle piece?
Two completely different scenarios requiring different flashing systems.
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You’re looking at sidewall vs. headwall flashing.
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That is a poor detail, Mark.
Step flashing is installed at every course of shingles applied.
See this video here; it might help.
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The water will run parallel to the bend in the step flashing and away from the bend in the head wall flashing.
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If you use that headwall flashing where a sloped roof meets a sidewall, would you put it on top of the shingles, or would you put it under the shingles? If you visualize each of those scenarios, you will see why it will not work either way.
You need to be both on top, and underneath the shingles, per se., much in the same way the shingles themselves are on top of the one below, but under the one above.
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what Marcel said…
Really. CMI. 
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I can see why its confusing for you. This is not a completed assembly, there are no roofing substrate under and over the step flashing yet. It looks to be a picture of a roof renovation underway with the shingles/substrate yet, old removed and new laced and installed with the step flashing.
One of only two in southern Arizona.
Thanks Marcel , great video explanation.
James , that picture is exactly why I was confused, why would you use all the little ‘steps’ when you can use one full piece… Thanks for taking the time to look at the pic and explaining it to me.
Thanks also Ryan and Larry.
Ryan , to your note, here is a Nachi pic… with flashing on top. But now looking at the pic I see that headwall flashing is on a different angled roof - the roof to the wall. I thought it was the same as - the roof to the wall but sloped down wards like in the step flashing pic.
Thanks again all for helping me out.
Though I prefer step flashing, angle or headwall flashing at the sloped roof/sidewall connection is common in my area and allowed per IRC 2018.
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I cant imagine how that could even work …
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By common you mean lazy and more likely to leak. With a continuous piece of flashing you would have to have all the shingles cover the flashing which then sits on the underlayment. If you get rain water(especially with wind driven rain) that hits the flashing, guess what? The rain water gets deflected under all of the shingles and onto the underlayment below and will leak at all the shingle nail shaft penetrations, tears in the underlayment or other vulnerable area.
With step flashing, each shingle course laps with a piece of step flashing so the rain water gets diverted onto a lower piece of shingle. Now there are still nails the water can get to, but it’s the nail heads above 2 layers of shingles(less likely to leak) versus the nail shaft through the underlayment(more likely to leak) of a continuous flashing install.
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True.
It was once in our code cycle and now it’s gone. Pretty sad really because a builder knows the continuous angle flashing is inferior.
True, but the IRC does also say that shingle manufacturer instructions must be followed. Do we know of any shingle makers who specify either type? I don’t want to look them all up, lol, but GAF Timberline, a popular shingle in my area, specifies step flashing.
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Good point. I suppose it is up to the inspector to decide if a call out or recommendation is needed. In fact, using “popular shingle in the area” in a good narrative would help the client IMO.
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Evening, Mark. I will try.
A roof deck and sidewall move independently. Typically a 1" inch gap separates the two structural components.
A chimney, the same thing. The chimney moves independently of a roof deck. Meaning the flashing at that wall/roof intersection will have to move independently of one another.
Step flashing are strips that fit under every shingle. The step flashing is secured/anchored to the wall allowing the shingle to move with the deck of the roof. As mentioned, The wall and roof deck move independently. The wall is flashed again with a counter flashing and secured against the wall leaving the roof deck and roof covering to move independently.
I hope that helped.
Maybe internachi can create a “certified flashing inspector” designation to help clear up these types of issues.
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