I looked up into my attic today, for the first time since we moved in (3 years or so).
Discovered quite a bit of what looks like mold, black and white around the box/housing that juts out up from the roof and accommodates the chimney. It definitely wasn't there when the home inspection was done.
I have no experience/knowledge in construction or mold mitigation, but I realize the mold grows where moisture is. So...
-Does this mean the "chimney box" is letting in water (even if there aren't leaks anywhere in the interior of the house)?
-Does this look really bad? Like should we all expect cancer and asthma?
-Before calling a pro in, should I know/do anything, may be clean it up myself?

Any feedback from someone knowledgeable would be very appreciated.

 

Welcome to the forums!

First thing you need to do is find and fix the leak! You'll also need to poke around on that sheet of plywood to determine if it can be salvaged or needs replacing. I wouldn't be overly concerned with the air quality unless you or yours already have respiratory issues.

 

Your attic IS a part of the interior of the house.

You're just lucky that there hasn't been enough of a leak to allow the water to hit the sheetrock.

Cancer and asthma.... not likely.

Can you post a pic or two of the chimney work on the outside of the house.
Is it brick or just a framed chimney ?

 

Wow, thanks for such quick responses! A bit difficult to get a good shot of the chimney from outside, it's high up and there are tree branches in front of it. From what I can see it's not brick. Just has the same siding around it that the the rest of the house does. Cant see the spot where it meets the roof...
So it's definitely a water leak then...

 

You can only tell so much from the attic side, someone will have to get on the roof to inspect.
It's been leaking for awhile although so far the damage appears to minimal, it will get worse if it's not addressed!

 

Yes, there is definitely a leak as that is the only way the plywood would turn black like that. More likely as not it is a flashing issue.

 

If it's the chimney flashing why would the leak show up way higher up on the roof?
I'd be looking for no over hang on the shingles, no drip edge, or tree damage to those end shingles.
"Over hanging limbs" sends up a red flag to me.
Never good idea to have trees or limbs anywhere near the house.
It can cause all kinds of issues with the foundation, roof and siding.
Any roofer can remove the shingles in that area and replace that section of plywood then weave new shingles in.
Anyone else find it odd that there's what looks like a cut off truss up there?

 

It's not a truss. It's the framing that the box around the chimney is attached to. I labeled the diagram how I think it's built. The bottom blue line is where the box joins the roof. That would be where the flashing should be to waterproof it.