Black Roof Sheating

[Jim B. Robinson]

I'm currently studying insulation/ventilation of attics and performed some attic inspections for friends. The attached photos are from a 30+ year old 2 story house. The soffit venting is totally blocked with batt insulation and no baffles exist, but has 4 roof vents. Outside air is leaking in through the gable end at the masonry-chimney/vinyl siding junction due to a hack siding job - you can see through to the outside and snow is visible on the insulation. Age of asphalt shingles unknown.

Re: the roof sheathing: Does this look like mold/mildew? I'm not sure what I would report to the client in this case as I can't be conclusive.

Thanks, Jim

[James Kiser]

I would call it moisture stains and refer it to a specialist.

[Jerry Peck]

I would call it moisture stains and refer it to a specialist.


What kind of "specialist" and why?

[Matt Fellman]

Unfortunately, a very common scenario... at least around my area. It's mold from a lack of ventilation and/or an excessive amount of moisture.

They can have a mold specialist come in if they'd like to identify the specific type (not sure why anyone cares) - Ultimately, the plywood will need to be replaced if/when it's weakened from the moisture (of course the best time to do this is when the roof is replaced). And the ventilation needs to be corrected and any sources of excessive moisture eliminated (route fans properly outisde, etc.).

The worst cases of this I see is where the roof has just been replaced over the top of the damaged plywood. It's hard to explain to a person that they just wasted $8,000.

[James Kiser]

What kind of "specialist" and why?

If he's not sure what to report and thinks it could be mold than he needs to defer it to mold specialist to confirm or deny

Could also be where moisture freezes on the plywood and turn dark

[Jerry Peck]

If he's not sure what to report and thinks it could be mold than he needs to defer it to mold specialist to confirm or deny


Why?

See Matt's post above: "They can have a mold specialist come in if they'd like to identify the specific type (not sure why anyone cares)"

[John Dirks Jr]

I would recommend adding a ridge vent.

Is there an eave overhang? If so, does it have ventilated soffit material? If it does, baffles should be added at the eaves to prevent the insulation from blocking airflow.

If you correct the moisture with better ventilation, the mold will die off.

[Ken Rowe]

I agree with Matt. It's mold. With plywood sheeting it's pretty common for the laminates to start separating due to the high heat and humidity also. Since the attic should be sealed from the rest of the house there shouldn't be much issue with the mold causing air quality problems in the living area, but the roof sheeting should be replaced at the next re-roof.

In the mean time I'd suggest adding ventilation. 50% ridge and 50% soffit. And, getting all exhaust fans etc vented to the exterior.

[Jim B. Robinson]

Thanks for the replies, appreciated.

I did mention to the owner that soffit ventilation requires attention - ie. install baffles to create a space between the insulation and roof sheathing to promote proper airflow. The soffit overhang is 16"-18" with perf alum soffit. It is unknown if the the siding installers went over an existing wood soffit.