Thread: Black Roof Sheathing

I would like some input on the cause of this attic conditon. The sheathing in this attic was very black and discolored. But if you look at the picture I posted you will notice the abrupt change at the ridge. I am thinking the sheathing may have been like this when it was installed. This part of the house was an addition built in the 1980's. There was one gable vent and three roof vents. Fiberglass insulation was installed with a paper vapor barrier. Area was above bedrooms and one bathroom. Crawl space did not have a plastic moisture barrier.

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I would say that almost certainly the sheathing wasn't like that when it was installed. The black part likely faces north or east (no sun) while the other side likely faces west or south (lots of sun).

There's a lack of ventilation (probably soffit vents blocked with insulation) or an excessive amount of moisture (bath fans vented into the attic or just hanging by a roof vent?)

The black is basically mold. If/when enough moisture hits the plywood it causes a de-lamination of the thin sheets of wood that make up the board. This causes the decking to lose a lot of it's strength. The best time to attack this is when the roof is done. Unfortunatly, people do layer-over roofs and don't replace this damaged product.

I see this condition fairly frequently up here in the soggy NW. I think the biggest thing to fear is what the 'mold police' are going to say. I personally don't think it's a problem of any kind to people in the house. As for structurally, it does cause a weakening of the roof decking but I've never seen a failure or even any abnormal deflection as a result. I typically write it up as a need for more vents and/or less moisture and additional testing, as desired, for mold.

Gregg,

Or Recycled Fire Damaged sheathing with the rafters replaced.

Hey Billy,

Some people may read this and actually think you are serious.

Originally Posted by Brandon Whitmore

Hey Billy,

Some people may read this and actually think you are serious.

Brandon,

If you look at Greg's location ( Charleston West Virgina) not known for the north west moisture problems.

And looking at the blow ups of the posted photos and stated addition 1980's you feel that a past fire & salvage rebuild is out of the question?

Post-fire it would have been painted/sealed. If not, it would still smell like the inside of a fireplace and I hope the OP would have mentioned that. If not, maybe you're onto something...

btw... I'm intrigued, does water not evaporate in West Virginia?

Originally Posted by Greg Jenkins

I would like some input on the cause of this attic conditon. The sheathing in this attic was very black and discolored. But if you look at the picture I posted you will notice the abrupt change at the ridge. I am thinking the sheathing may have been like this when it was installed. This part of the house was an addition built in the 1980's. There was one gable vent and three roof vents. Fiberglass insulation was installed with a paper vapor barrier. Area was above bedrooms and one bathroom. Crawl space did not have a plastic moisture barrier.

Originally Posted by Matt Fellman

Post-fire it would have been painted/sealed. If not, it would still smell like the inside of a fireplace and I hope the OP would have mentioned that. If not, maybe you're onto something...

btw... I'm intrigued, does water not evaporate in West Virginia?

Matt,
I'm sure you see a lot of things in the North West we do not see here.

Gregg was there we were not.

He asked for some input.

The abrupt change at the ridge and lack of growth on the rafters would not rule out 25 year old smoke damage. IMHO. Could they have washed the sheathing B-4 reinstallation?

Now I'm intrigued Does Mold not grow on rafters or the West or South side of an attic?

Pictures of before and after dry ice cleaned fire damaged sheathing.

Your photos indicated some rust condition to the nails. I see this all the time in North Calif. Q. did you push up on areas of the plywood to check and see if it was loose. This is common for a blackening/mold condition to rust out the nails and damage the plywood. I bet if you push up on areas of the plywood its loose.

Best

RON

Originally Posted by Greg Jenkins

I would like some input on the cause of this attic conditon. The sheathing in this attic was very black and discolored. But if you look at the picture I posted you will notice the abrupt change at the ridge. I am thinking the sheathing may have been like this when it was installed. This part of the house was an addition built in the 1980's. There was one gable vent and three roof vents. Fiberglass insulation was installed with a paper vapor barrier. Area was above bedrooms and one bathroom. Crawl space did not have a plastic moisture barrier.

That crawl space with no moisture barrier can contribute moisture in the attic.

Originally Posted by Billy Stephens

Matt,

Now I'm intrigued Does Mold not grow on rafters or the West or South side of an attic?

Yep, usually the way it looks... the underside of the sheathing gets colder and the moisture condenses on it. I've never seen the rafters effected, even when the sheathing is much worse. The most common place to find it is above a one room apartment with 10 people living in it.

Originally Posted by Matt Fellman

-- one room apartment with 10 people living in it.

Only 10 people?

The trend here is Multi Extended Family's.

If it's Black mold it's from a past evident.
The discoloration is confined to a very thin depth on the surface.( Small triangular non discolored area pushed out by roof fastener top right of Photo. )

Thanks for the input. I don't believe it was fire related. No odor, charred material or other evidence of fire. I believe it is a mold/mildew related problem. I do believe the darkest sheathing was on the north side. The house had a damp crawl space as well. I probed the sheathing and it is stll solid. The attic also appeared to be well vented. It's possible that the problem has been addressed and I am seeing symptoms of a previous moisture problem.

Brandon,

If you look at Greg's location ( Charleston West Virgina) not known for the north west moisture problems.

And looking at the blow ups of the posted photos and stated addition 1980's you feel that a past fire & salvage rebuild is out of the question?

Billy,

My apologies.... I really thought you were joking and left out a smiley face. Matt answered the way I would have in the next post. I do side work with a fire and water restoration company when it is slow. Smoke damaged sheathing will smell very strong in my opinion unless sealed over. I guess really old smoke damage may quit smelling, ya never know.

Originally Posted by Brandon Whitmore

---I do side work with a fire and water restoration company when it is slow.

Brandon,

No offense taken.

I've been doing the same lately ( Fire & Water Restoration ) last job 6200 sq. ft lighting ran in on alarm phone line.

Sooner or later He's going to call and I can say " Sure like to help you but I'm all booked up."

Best practice is to remove anything with smoke odor.

While I never see it around here, you may be dealing with fire-retardant plywood. (FRT) plywood
This material was used in the 80's, and, from what I remember from magazine articles, it does result in a darker colored surface. Unfortunately, it also results in a weakened roof deck. Big stink arose after it was known that it was prone to failures. I would do a little more reading on FRT to see if the symptoms apply. Also, if possible, probe the material for signs of delamination.

Never heard of dry ice restoration before this post. Learn something new everyday. Check out this video.

YouTube - dry ice blasting mold remedation and fire restoration

Originally Posted by Matt Fellman

As for structurally, it does cause a weakening of the roof decking but I've never seen a failure or even any abnormal deflection as a result. I typically write it up as a need for more vents and/or less moisture and additional testing, as desired, for mold.

Hello from the North,

I am currently inspecting in Nova Scotia, Canada (another cold wet climate) and have come across a similar situation. In my case the house is a semi- detached, with one roof slope facing north and the other facing south. The entire surface of the roof sheathing in both attics was blackened with the darker sections along the north facing slope. There are nails that show signs of rusting and the darkening appears to be only on the surface of the sheathing. The roof was recently resurfaced and the “white or light” triangular sections are present around the new nail holes.

The ventilation in both attics consisted of ridge, gable, and soffit (between every truss). Although I did not measure the available area, it appeared that adequate ventilation was in place.

An irregularity in the shingles on the front and back were noted which seemed to correspond to the collapsed or sagging sheathing as seen in the photo. There were collapsed or sagging sections both on the north and south facing slopes.

Initially I was unable to locate the ducting for the upstairs bathroom exhaust fan. Additionally there was no exhaust point located on the exterior. I did a bit more investigation and found that the fan in both cases vented into the soffit. In the location of the termination point of the vent duct the sheathing was notably more darkened (see photo).

Q1: With the seemingly sufficient ventilation is it possible that the problem no longer persists?

Q2: Is it possible that the damaged sheathing may have occurred during the reproofing process as a result of a weakened state of the sheathing due to excessively high moisture within the attic?

Q3: What recommendations should be made? Relocate the exhaust point of the fan? Install an exhaust on the outside of the soffit? Replace the damaged sheathing when the roof covering is next replaced?

Q4: Should this be considered as an ongoing issue and is this of major concern given the amount of ventilation currently in place?


Looking forward to the feedback. Enjoying reading all your posts.

[quote=Peter D. Lewis;167495]Hello from the North,

Q1: With the seemingly sufficient ventilation is it possible that the problem no longer persists?

Q2: Is it possible that the damaged sheathing may have occurred during the reproofing process as a result of a weakened state of the sheathing due to excessively high moisture within the attic?

Q3: What recommendations should be made? Relocate the exhaust point of the fan? Install an exhaust on the outside of the soffit? Replace the damaged sheathing when the roof covering is next replaced?

Q4: Should this be considered as an ongoing issue and is this of major concern given the amount of ventilation currently in place


Hi Peter,
From your images it appears the nails with the diamonds around them are older nails. The diamond shape around them is caused by zink leaching out from the nails preventing mold growth near the nail, so those would be older nails. The problem with mold growth in the attic may be ongoing.

There are many posibilities for excess moisture in the attic. You mention ridge and gable vents. Imballanced ventilation openings in an attic can cause areas of stagnant air in an attic. An improperly ballanced HVAC system can cause rooms benieth and attic to have higher pressure resulting in air/moisture exfitration from those rooms into the attic through cracks and openings. The exhause ducting from bathrooms or kitchens may have leaks and as you stated, the exhast from those fans was into the attic. The source(s) of moisture must be addressed prior to any mold remediation.

I would recommend attic ventilation, damaged sheathing, and exhaust fans into the attic be professionally evaluated and repaired with improvements made as needed. I would also recommend the mold/mildew be professionally evaluated and remediated in order to confirm the moisture problem has been solved.

Thank you for the advice.

Peter D. Lewis

The sheathing should have been replaced, by the looks of it. Where that H-clip is popped, somebody may have slammed down a bundle of shingles. One spot could be blocked up from below. But if there is sagging in other places, it would seem there is a problem there that you need to point out to your client. It may be a case of getting the roofers back to redo the whole thing, and at that point, your client might not want to proceed.

Is soffit venting of the exhausts normal for NS? I would call for roof vents here, but we don't get the thick white stuff like you do. What about wind blowing moisture back in under the eaves?

I see this in older homes around here. Homes are not tight back then and wet crawl spaces are the norm. Moist air passing through the home from the crawl space and added showers and cooking caused water to collect on winters cold roof surfaces. When the roof covering was replaced, spongy plywood areas where replaced.