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Roofing/open valley roofing


Hi Brad,

I Just had my roof re-done (february). We have an open valley with a "W" type sheet metal product down the run. The outside of a portion of the sheet metal appears to be lifting up under a section of shingles. It looks like a large bump underneath the shingles, like something was left underneath them and was pushing them up (that's what I originally thought it was). When I examined the shingles closer, I pushed my foot down on the bump and found that It was the sheet metal bulging up below the shingles.I could push the shingles down and hear the metal buckle below them as I pushed them down flat. When I lifted my weight off of the shingles, the sheet metal sprung back and formed the bump again. It was almost like an air bubble. The roofer looked at the spot and said that it was due to the cool weather, and that this can cause the sheet metal to expand, lift and contract. He stated that it would sit flat when the warmer weather arrived and hit the roof.

Not sure if I've explained this well enough for you to understand? If you can, does this sound right? I've looked at other open valleys and have not seen this issue on any of them.

Please, let me know your thoughts.



If the metal goes down with your foot then it would go down with a nail(s). In other words, there should have been more nails there. He missed nailing it or he skimped on the nails. If it's a buckle in the actual metal that could be due to a bend in the valley and the metal does not form to the bend. When that happens he should have made a seam in the metal. Let's say there some kind of 1 degree bend in the rafter. You lay the metal down and it lays on the wood at the top and the bottom but is slightly in the air in the middle. If he tried to force it down in that scenario it would buckle. What you do then is to make a seam there so one piece ends there and another takes off at the new angle. Or it could be as simple as no problem with the angle but he did not do enough nails. This will not settle down over time and if you're lucky for it to go down in warm weather it will be back up next winter. The roofer screwed up either way. Your options are to permanently stand there or take the shingles apart and nail it. And then do you just fix the one spot or is the rest not nailed properly and it's just the one spot that popped up so far and more will happen later?



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Brad Zacharia


All aspects of residential Roofing. This includes shingles and flat (low slope) roofs. I have knowledge in the installation as well as the design of roofs from an engineering standpoint.


I have been doing roofing for 40 years. This was my father's business and I took it over in 1980.

I have written responses to artcles that I felt needed a response to and those responses have been published in roofing trade magazines.

BSEE Drexel University

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