Black residue around water heater roof vent

[Gtomike06]

I had all my galvanized pipe replaced earlier this year by a local plumbing company along with my hot water heater. I've been having some ac issues and it looks like when they were working in the breezeway attic they crushed some ductwork. When I was up there I noticed the cpvc was against the water heater vent pipe. I got some wire and tied the cpvc back some and notched the sheet rock to move the vent to give me proper clearance.

While I was up there I noticed the sheathing on the roof and rafters around the vent was solid black. The vent pipe has metal tape at every connection and is all class b pipe and none of it is black at all. It's routed kind of goofy but it appears to have the proper upward slope. I know when the water heater kicks on i can see the fumes coming out of the vent on the roof. Is this a hazard or what caused all the residue?

 

[Dj2]

Black soot could be a result of a burner too rich or wrong air/gas mix. Make sure the area around the WH is clear and vent is clean, to allow air in. The color of the burner flame can reveal the cause of the built up soot.

 

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[Gtomike06]

Why would it collect on the bottom of the roof? I would think it would collect in the ceiling of the room or around the roof jack outside. I'm not expert though.

I would hope they would have checked the flame but since they left the cpvc against the flue pipe I'm not sure they would have.

I did notice that the roof jack is different than a lot of them I see in pictures I'm not sure if mine is just an old style one or something though.

 

[Dj2]

Quote: "Why would it collect on the bottom of the roof?"
Maybe because it found an escape there.

Quote: "I did notice that the roof jack is different than a lot of them I see in pictures I'm not sure if mine is just an old style one or something though."
You mean the cap? the shape of the cap doesn't matter, What matters is that the cap stops water from getting in the vent and doesn't stop CO2 from getting out.