Roof to wall flashing

I am redoing the siding (T1-11) above a shingle roof-to-wall junction on my house and the existing steel flashing is quite rusted. Before putting the siding over it I have several questions about whether I should replace it and if so, how:

1. Diagrams I've found online talk about "step flashing", which seems to mean short pieces overlapped - I get the reason for overlapping butt ends but no reason is given for the short pieces. Is there a reason for using short pieces, or can the flashing be continuous, say from a roll? It seems strange to be cutting short pieces from a 50' roll for this. I haven't noticed flashing sold in these short lengths. With steel, cutting would be exposing uncoated surface.
2. Before messing with the shingles (they're getting a little brittle) will I be able to just tug the flashing out from under them to replace? Or will I need to remove shingle nails? I'm trying to get a feel for whether this (not expected) part of the project is going to be simple or complicated . . .
3. Can I use vinyl flashing to replace the existing flashing?

 

Step flashing is the way to go on a wall to roof transition. Each small piece goes under each row of shingles and is nailed off on the vertical section of the wall. Start at the bottom and work your way up to the peak. Roll flashing would only be used for a valley application where two different roof sections meet. Purchase the step flashing already bent. Only your investigation will tell if you have to remove nails under the shingles or not.

 

Thanks, that makes sense. So now more questions of course: locally, prebent is only available in galv. steel, so that eliminates the decision about material. Which end goes up, on the wall, the 7" (long end)?

 

So the situation is:

1. Old flashing was done in odd lengths, not the width of the shingles
2. Old will be hard to remove without damaging the shingles

And the unavoidable new questions:

1. Can I install new galvanized flashing over the old?
2. Does the new flashing need to be nailed to the roof or is only the wall OK?
3. I'm thinking there's a chance if the 2" end goes under the shingles that I can slip them under without having to bend the shingles too much
4. Finally, what would you do?

 

Step flashings should actually only nailed to the roof, not to the wall. Sometimes the siding nails pierce the flashing but there is no reason to purposely nail them to the wall.

If you don't want to replace the shingles, you could go over the old, but they won't lay as flat. If the roof is ever replaced at some point in the future, you could specify all new step flashing at that time. The bigger the step shingle, the better. I would not be satisfied with a 2" step flashing. 4x4x8 is much better. You really don't need to bend the shingle much at all if you are going over the existing.

Also, we assume you are talking about going up a rake, where the shingles are perpendicular to the wall and each row is step-flashed individually (which I agree is better than a continuous flashing)... and that you're not talking about the top row of shingles under a gable end, where the shingles are parallel to the wall, where a continuous wall flashing would be used.

 

• XSLEEPER WROTE: . . . we assume you are talking about going up a rake, where the shingles are perpendicular to the wall and each row is step-flashed individually (which I agree is better than a continuous flashing)...

Yes, going up the rake where it meets a wall under a gable end. The existing flashing is continuous, or irregularly-spaced between sections - like continuous runs of 4+ feet, definitely not the step kind.

• XSLEEPER WROTE: Step flashings should actually only nailed to the roof, not to the wall. Sometimes the siding nails pierce the flashing but there is no reason to purposely nail them to the wall.
  

They will probably end up being fastened to the wall with the trim under the bottom edge of siding. What I'm still not getting is whether they need to be nailed at all. To nail the new step flashing to the roof I have to bend the upper shingle way up. Does it matter? For example, I'm looking at a FEMA diagram (Tech Fact Sheet #23) and it says nothing about fastening the step flashing except to use "flashing cement at joints".

Also, what should the overlap be on the steps?

• XSLEEPER WROTE: If you don't want to replace the shingles, you could go over the old, but they won't lay as flat. If the roof is ever replaced at some point in the future, you could specify all new step flashing at that time. The bigger the step shingle, the better. I would not be satisfied with a 2" step flashing. 4x4x8 is much better. You really don't need to bend the shingle much at all if you are going over the existing.

That sounds perfect, I don't want to set things up in a way that the flashing can't be done right when I have the roof done. I found 3x4x7 aluminum step at Lowes. Will install with the 4" side on the wall and will do it over the old steel flashing I guess.

Thanks for all the help!