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suobs 01-19-2014 11:37 AM

Step flashing and siding problem
Replacing sheet T1-11 siding. Old (rotted) siding at a roof to wall juncture is glued to the old continuous steel flashing with roofing cement. The flashing was installed over the siding. I need to remove the siding and the plan was to gracefully and quickly disengage it from the flashing, slide the old flashing out from under the roof shingles, replace with aluminum step flashing, put the T1-11 over the flashing, and re-adhere the shingles to the flashing and each other.

I have a limited window of time to do this in and it's getting complicated lifting the old shingles because the shingles are threatening to break, and I'm not sure it'll be easier in hot weather. It's been in the 40s at night, maybe the shingles would be less fragile in hot weather?

I'm wondering about NOT replacing the flashing (assuming I can get the remaining old siding off the back of it), putting up a new flashing overlapping the old flashing down only to the level of the shingles (under the siding but not under the shingles), and sealing the new flashing to the shingles - or at least to the old flashing.

Make any sense, or any other ideas? I guess another alternative is removing the old shingles and replacing them, but the roof is getting old and they will be difficult to match color.

oldognewtrick 01-19-2014 12:50 PM

I would leave the existing flashing and replace the siding only, IF you can remove the siding without destroying the flashing and shingles. If the shingles have any age to them, they may be impossible to tie into with all the roof cement applied to them. The siding should be over the wall flashing and be sure to leave an air space between the siding and roof shingles so you don't wick water on the end grain of the siding.

Here is the Florida code requiring all the roof cement.

suobs 01-19-2014 01:20 PM

Just found I can't leave all existing flashing - some had to be cut off, leaving only about 1" of vertical. Can I use vinyl flashing over it on vertical? How to tie to existing flashing?

oldognewtrick 01-19-2014 01:26 PM

You will need a minimum of 3" turned up the wall. At this point, pull out the shingles, match as close as possible, install new flashing, shingles, roof cement and siding.

suobs 01-20-2014 04:19 AM

Thanks, those are great answers.

Thanks for the code link also, but as always code generates more questions than answers. Do you know:
  • Do you know how step flashing is installed? Option B/Detail C say nothing about flashing cement, although Option A/Detail B (for continuous flashing) shows a continuous flashing embedded in "flashing cement", whatever that is (Detail B calls it "mastic"). But step flashing not sealed or nailed to anything? I'm not finding 10" precut metal flashing ("metal shingles") anywhere.
  • Any idea what this means: "Roof planes that butt against vertical walls shall be step flashed with 10 in. long metal shingles which are 2 in. wider than the exposed face of the roofing shingles (see Detail C)."? Width is of the section that lays on the roof, or the total width of the flashing piece?
  • How do roofers replace flashing when the siding is up already? Because the roof I'm working over is on an addition, they must have faced this problem and solved it by attaching the flashing OVER the siding panels. As a result, the siding is mush in the vicinity of the flashing.
  • What the heck is bull flashing? You'll get some surprising answers with a Google search.

oldognewtrick 01-20-2014 05:55 AM

Well, sometimes you have to man up and grab the "Bull" by the ...oh never mind. ;)

Flashing a wall is really not that difficult. It takes a little time and patience.

-Carefully remove the shingles one full shingle width away from the wall, using a shingle pry bar. Working one shingle at a time break the seal strip on each shingle. You should have a zig zag pattern running up the roof next to the wall as you don't want all the butt joints lining up on top of each other. They should be at least 6" in the stagger.

-Clean the roof of old roofing underlayment and nails.

-Take you skill saw and set it for the depth of the siding and no deeper. Lay it on its edge and from the bottom to the top cut a straight line up the wall. You should be removing about 4" of siding. More about this later.

-Install the new shingles, one at a time over new roof underlayment. Install a piece of step flashing on each shingle as you go up the wall with one nail in the upper corner away from the wall. Apply your mastic as you go. You will get some on you, it's unavoidable.

-When the shingles are complete, take a piece of pressure treated 1x4 and fill in the void you created in the wall. Caulk the edge where the cut was made to the new board. If you made a straight cut, it will be a fine line.

-After the install is complete, prime and paint the new boards to match the siding. I would suggest primming the new trim board on all sides and also the edge you cut on the existing siding.

-Go to a local roofing supply house (not one of the Big Box Stores) and get your shingles, underlayment, flashing, caulk and any advise you need.

AND MOST IMPORTANT, IF YOU ARE NOT COMFORTABLE WORKING ON A ROOF, HIRE A PROFESSIONAL. Falls can permanently injure or kill you and yes more accidents happen on low slope, single story roofs. Never work alone, have a helper present when you are there. And what ever time you think it's going to take to do the repair, double it at least.

WD-40 is great for getting roof cement off you and your tools by the way.

bud16415 01-20-2014 07:00 AM

I would do exactly as oldog Rx the only thing I do different is adjust how much siding I trim up based on the other trim on the house. Sometimes soffits have a similar detail at the top and then I cut it so I don't have to rip the treated board. I also have a Z bent piece if its wood siding to slip up under the siding and over the new piece that acts as a drip edge.

The idea you have to see with step flashing is they are weaved in just like the shingles. A straight flashing relies on the mastic too much steps done properly will shed water just like shingles.

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