I’m new to home inspecting, but not to construction, and I’ve never seen OSB like this. It looks almost as if it was intentionally charred. At first I thought it was moisture damage and fungal growth, but on closer inspection I found no elevated moisture, no fungal or mold growth, and no water intrusion. Can anyone help me out here?
Looks like it was a ventilation issue at one point. A lot of it has already been replaced.
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Some OSB has been replaced. So somebody knows something they are likely trying to hide. Almost looks like smoke damage, but the trusses are too clean.
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Possibly from being stacked wet before construction?
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Welcome aboard, David. From here it looks like possible microbial growth.
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How many sheets were coated with this black whatever? When manufacturing, they use ink to grade and label each sheet of ply. looking at the second pic, could it be spilled ink from the factory? 
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I would say at least half of the sheets looked like this. The strange thing is that adjoining sheets didn’t display the same “defect.” They may both have staining on them, but at their intersection there was a distinct change in pattern so I know it wasn’t moisture, and it most likely happened pre-construction because the staining was between the sheathing surface and the truss. Whatever it is was localized to the individual sheets.
Welcome David! Looks like microbial growth, at least in some areas, to me as well. I second JR on this one. You’re asking about the OSB but I see indications of possible microbial growth on the trusses as well.
Edit: Did you test for fungal or mold growth? How did you “find” that there was no fungal or mold growth?
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It is. It appears that a new roof was installed. IMHO the ‘stained’ OSB should have been removed or treated.
@ dvaughn6
Kevin makes a great point…microbial growth requires and feeds on moist, organic material.
One possible scenario: During initial construction, some OSB boards are covered and some are exposed to moisture prior to being installed. One dry (acceptable moisture content per construction standards) OSB panel is installed and then the adjacent panel that was exposed to moisture is installed. The microbial growth will only feed on moist, organic material which is why you may see microbial growth on one panel and nothing on the adjacent panel.
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That’s not what happened.
So did you verify that there is no more growth?
Welcome to the MB @dvaughn6. First, some observations, then some questions for you…
Except microbial growth on a single sheet wouldn’t create perfect lines (red arrows) in the middle of a sheet. I’m curious what is on these trusses (rainbow arrows), looks like something was applied and sort of cleaned off…
I agree with Randy. At first I thought it was char marks until I blew up the pictures and realized I was looking at black finger prints. Somebody’s hands got very dirty…
Finger prints in circle, note black wood around black nails (colored arrows), all the other nails look shiny new…
Also, this sure looks like wood putty…
The flaked OSB at the ridge vent looks too clean where it is flaked. Doesn’t look like it was wet long enough to make fungi that would create such a solid and reflective surface. The black area has shiny spots, almost like it has surface char… I’m curious what the grey stuff is, more wood filler??
@dvaughn6 Q&A time:
How old is the house? Where is the home located? Did you check to see if any records of a fire at this address are available? Is it possible that the roof structure was built with recycled materials? (just trying to think outside the box) What ever happened there, someone tried to remediate/repair… How old was the roof? Do you pics of the outside? What was the gable end material? It appears to have some damage. Were there any prominent odors in the attic?
Smoke staining. For a moment I thought it was pyrolysis which I have seen a couple of times formed at the peak in some older, hot ass attics, which still may be the case here (you can see the truss members are discolored and lighten up as you go downward). But that is a big area for pyrolysis so I am voting smoke. Think kitchen fire, black smoke enters the attic and collects at the top, staining everything. Firemen soak it all, some of the OSB gets replaced eventually when a new roof is put on, and this is what it looks like now.
Maybe?
I suspect the OSB sheathing was changed at one point. Suspect, due to ventilation issues. Even now, the eaves are not dammed to prevent the blown in loose fill rockwool insulation from spilling over and deposited on to the open soffits. The 3rd image, #801 KB you see daylight at the far left eaves but no insulation eave dams.
Some of the OBS was likely purchased from a recycled building materials dealer. One OSB sheet, #801 KB, has a clear outline of smoke stains divided by clear OSB. As if a sheet of material was covering that section of OSB from smoke preventing it from being stained.
Staining OSB sheathing.
Stained upper chords and webs.
Poor attic/roof venting.
Suspect, microbial growth.
Request disclosure from the venders agent if there was ever a fire in the home.
Request disclosure from the venders agent was any remediation work done in the attic.
Kennesaw, GA
Built in 1985
No disclosure of house fires
That does look like a paint run. That attic has quite a bit going on…
David, it looks like you have a very bright flashlight. Here’s a little photography tip, next time you are in an attic with white insulation, shine your flashlight at the insulation to create ambient light for pictures of the sheathing or anything else for that matter. If the pictures are still dark, use the flash on your camera while shinning your flashlight down. This will eliminate the colored ring your flashlight makes, and makes for a better photo.
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True pyrolysis is something that we home inspectors rarely see because 1) it is rare in residential situations, and 2) it usually occurs in confined, dead or inert air conditions.
Agree. Looks like smoke in places, looks like mold-like substance in places, looks like some water issues in places, looks like replaced decking in places, looks like some decking might have been stored wet before installation in places, and fingerprints suggest someone was up there doing some evaluation of the surfaces.
David…good call out. Report what you see and reasons for recommending further evaluation.
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It looks like traces of a preservative solution, similar to an asphalt primer.
Like antiseptic on a telephone pole.
There was a time when asphalt primer was applied to OSB to counteract moisture condensing inside the roof.(Ditto for walls)
My guess is that when the roof was sheathing, they primed(asphalt) it, flipped the OSB over, and nailed it down.
Some of the messy looking areas were replaced with new OSB along with the roofing material.
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