Thread: Roof ply is turning black

I live in a Condo in NH and this roof was replaced in November 2008. Since the recent cold weather we have a unit owner that noticed frost & black decking which they are concerned is mold. I spoke to the Roofing company that did the installation and a second roofer that did other units for us and they're thoughts are that the attic does not have sufficient insulation which is causing heat loss from their home which is causing condensation that is causing the black & frost. I've also been told that the plywood was older and that's why it turned black, mold doesn't spread that uniformly.
Any insight would be much appreciated.

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Hard to tell without seeing the rest of the attic but... given that the discoloration is confined to individual panels, and does not appear to be extending to adjacent panels, the discolored material may 1) be older material, with newer sheathing installed above it or 2) may have been discolored when installed.

If this is an ongoing process, I would expect to see at least some evidence of discoloration on the "newer" sheathing adjacent to the discolored panels.

Check the ventilation. Ventilation of the attic is supposed to be present to prevent moisture buildup.

Besides providing adequate ventilation (if needed), make sure you air seal all penetrations into the attic, and all ducts.

First pict looks like water damage to left. Nails look rusted and there is a 16 p nail through roof.

First check if the condo unit under roof area in question has a humidifier. If they have a humidifier or if kitchen is there you have excess moisture being generated by owner that is migrating up to roof deck and condensing. Need to stop excess humidity

Example: I put a new roof on including replacing the roof deck in summer. Fall came and owner turned on heat (Forced Hot Air). Owner likes to keep house at 80. To combat the dry heat they had a big stand alone humidifier that they ran at maximum. The result was water condensing on the roof and running down like it was leaking. When I went to look a t the problem I was amazed to the quantity of water that was condensing. Ventilation was a partial solution (power vents) but the bottom line it was the owner and the amount of water they were putting in to the house

Check on what the units are doing that may cause the problem of moisture.

The dark decking is a light growth of mold caused from high mousture in the attic, caused from no/poor attic ventilation. We'll see this with excessive dampness/standing water in the crawl space or damp basements. Some cases when the occupant is producing (cooking, showering, washing, fish tank) too much moisture, it will overwhelm the attic ventilation, if any.
The reason certain panels are darker, these panel have been exposed to a high concentrate of the mold spores. This usually occurs when the plywood is delivered, and sets on-site. The top piece of plywood is exposed to the atmosphere and all those vegetation spores. This also protects sheathing beneath.

I have seen where condo roof sheathing was replaced. They don't necessary replace all the sheathing, just the sheets that were readily removable.
So my guess is that the lower sheets are the original mold-stained plywood, and the upper sheets are those that were replaced.

The moisture problem was not properly dealt with, because there is frost and new mould growth. The condo association needs to get the remediation company back in to repair the repair.
The vinyl vent hose is an example of a flaky installation. It should be a metal duct. All the joints should be taped and it should be wrapped to minimize condensation.
Adding insulation is not the cure if there are air leaks into the attic. First stop all movement of warm moist air into the attic. This means removing insulation from around all penetrations, sealing all the holes. Ensure the attic has adequate ventilation. Then go ahead and blow in some more insulation if you want.
The mold growth will die off if the moisture is reduced.