Shingles transition pitch from 3/12 to 6/12. Flashing transition - Grace IWC or Copper?

Good morning, everyone,

I have finally completed adding barn roof addition to the main house stucture. The new roof is 15-degrees in slope (approx. 3.2/12), which attaches to main roof that is 30-degrees (6.5/12). The transition is pretty mild in general. The 3/12 roof has double layer of OC Deck Defense. I was planning to place Grace Ice and Water shield on roof transition and overlap bottom portion into double deck defense. I was also going to leave maybe a 3-4 inch bottom piece to actually lap over the layer of shingles (should the transition ever leak - it would move water back onto shingles instead of remaining between shingles and underlayment. I was going to have continuous shingles through transition. Since the angle change is small, I do not think they will crack overtime.

However, the home inspector recommends using metal to flash transition. This means I will have break in continuity of shingles. What I envision is continuing shingles up to and even slightly over the transition, then nail the metal flashing that will overlap a layer of shingles on 3/12 roof and go up a few inches on 6/12 roof. Then start new row of shingles with bottom edge butting up to transition bend. This may be less pretty than continuous shingles, but I do agree that it will probably be longer lasting.

What do you all think? Would Grace IWC work just as well as metal flashing? Would you suggest one or the other? And would you change anything from what I described to make it more watertight?

Thank you all for your help!

This is the photo of the transition. The roofing and chimney flashing are still old - I plan to replace everything with copper flashing.

You just need to use some 26 g steel valley metal at the transition on top of underlayment.
Thats it. 16” wide.

Personally, i’d just use the grace and make sure it overlaps the previous row of shingles as much as possible to not be visable. But i’d also have 100% confidence a good roofer could use nothing there and have no issues.


Thank you, roof_lover. Would the same rule apply to this metal as would be in the valley - i.e. tack the roofing nails next to this metal but do not penetrate the metal, which would allow it to expand and contract without deforming? Would I tack them above and below the transition and how frequently? Would extra thickness show up on the finished roof? And lastly, would it be a bad idea (despite adding more thickness) to apply Grace over or under this metal to help seal holes created by roofing nails? In case of leaks, this seal will prevent water intrusion?

No , i always penetrate my valley metal.
1/2 inch or so from the outside and every 6 inches or so.
For a beginner technique i would nail the top side of the valley metal only all the way across from side to side.
Then i would put my foot in the center crease of the transition as i nail the bottom of the valley metal.

If you use 26 g steel and nail it correctly
Then it will never warp or move.

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If the addition is secured properly to the house, which it seems to be, I would run those shingles right through the transition and wouldn’t even consider metal. Just make sure there isn’t a trough in the transition, adjust your courses accordingly and make sure there are no fasteners in transition area.


Yes there is not enough angle change to worry about in this case, as mentioned above no nails in the actual angle change, we roof about 6 houses a year with this same angle change (one of the house plans the contractor uses weroof for), we ice shield the low slope area, felt or synthetic steeper slope


@roof_lover, another question. I am a slow worker, but I was finally able to tend to transition yesterday. The roof is currently covered with green tarp, unsightly, but it works as I slowly work through this project. Nailed additional nails on top of lower slope decking to ensure plywood does not separate and remains tightly attached to the rafters. The plywoods touch each other at connection. Placed Grace IWS over the transition, the angle change is very small, but I reckon I did not guess exact angle to cut osb to be fully flush to steeper roof so there is a small (1/4-inch or a bit larger) gap between edge of one plywood as it butts up against the other roof angle. In other words, the bottom of plywood is tight against the steeper plywood, but the top of new plywood is not flush with steeper roof since I did not cut angle perfectly to be flush. Small gap there. So I am pretty set on using the 26G galvanized steel as you recommended to provide full shingle support over the transition and reduce likelihood of unsupported sagging.

One question I have - local stores here sell 31G metal in 50 ft rolls. I need 33.5 ft total, so I had to special order my steel in 26G. 31G seemed quite flimsy. However, 26G rolls came in 10ft lengths, so I will have to combine multiples together. Do you just butt them up together without overlap? I worry overlap will result in differential thickness as well as greater hardship to penetrate with roofing nails. Second question, I am using Hitachi nail gun at about 95 psi for good nail penetration. I think it can go up to 120 psi max (my compressor gets up to 125 psi). Do you have any difficulty nailing shingles through this 26G piece of flashing? And last question, the piece where it transitions, does the metal need to be bent there for a bend line or do I need it to bend in a rounded fashion around the transition? I have a metal brake I can bend perfectly there or I can simply let it curve around the bend.

Thanks again to everyone for all great advice!

Your gun will nail through the metal as if it wasn’t there. The seams should be overlapped,I prefer to have transition metal bent to the right angle.

Thank you so much! I got enough metal to cover 40 ft, so overlapping will be a non-issue.

This is the result - put it down this afternoon. Grace on the bottom to seal to decking, 26G galvanized steel next, then OC Deck Defense underlayment last. Grace will overlap over shingles, and OC does too. So double layer in case of leaks. Everything on this roof was waterproofed with copper, there better be no leaks. Haha. Metal provides fantastic smooth transition. Almost hard to tell where the transition is precisely. And sturdy so no issues with shingles sagging. Thanks everyone for great suggestions!

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When you shingle through the transition you are going to punch a bunch of holes through the metal.

The metal drains beneath the shingles on the lower slope.

Yes, the metal’s purpose was solely to bridge the transition, not necessarily as a flashing. If I used metal for flashing, then lower slope shingles would be separate from higher slope shingles, i.e. they would terminate over the bend, then flashing would be nailed only above the bend, then new row of shingles would start butting up to the bend and higher. I would have either left the flashing exposed (copper) or hidden it with a row simply glued on for looks. I like the looks of exposed copper, so visible is how I would have done it. But as most recommended just to transition slopes without any needed flashing, this is not really flashing but a transition piece. I decided to include metal since there is small gapping between two OBS surfaces and I did not want them to sag over time or be prone to easy cracking. Any extra purpose will be a benefit, so that is why I am mostly depending on Grace and OC underlayment for secondary water barrier.

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Overkill but if you’re happy with it that’s the main thing. It certainly won’t hurt anything. Done hundreds, if not thousands, of those without metal and never had an issue.

Thank you, @Tileman, you’re right, the transition is so smooth, it would have been okay even without this metal. But it seems a bit sturdier and will provide for less potential movement at the transition over time. With 7/16 OSB sheets, they have way too much give, so this metal sturdies the connection. I wish I used thicker OSB for this portion of the roof, but had to match the rest of the house…

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I would never fault a person for going the extra mile. Nice job!

The last ten foot section you did by the nail gun was perfect.
But if you havent shingled it yet
That section before hand had some wrinkles in it that are unacceptable.
You didnt get your foot all the way into the center of the transition all the way on that one…
Take the nails out across the bottom for about 6 feet and redo it if possible.
Shingling over wrinkled valley metal is worse than having none.
Any way, i think you know how to make it perfect In the future.
I’ll bet you got that forth section of valley metal perfect too.

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I would say to use both grace and copper or another type of metal.

Maybe a 032. Metal to match the roof color