Dry rot in fascia and sheathing not discovered by roofers

Hi. I would really appreciate some advice on a major issue that has arisen on a newly installed roof. I’m a new first-time homeowner. In August, I hired a roofing company to replace the old roof on my recently purchased home. They removed three layers of shingles, put plywood over the existing tongue and groove sheathing, and put the new shingles and flashing on. Now, about 2 months after installation, some black mold has appeared on the undersides of the tongue and groove sheathing in the attic. (I’m getting a professional mold / mildew assessment performed this coming week).

I’m baffled by the sudden appearance of black mold because the roofers installed ridge venting and smart vents, which would hopefully be as good or much better than previous ventilation. There had been evidence of previous water damage in the roof, but no black mold. The mold that has appeared is in the area where a chimney had previously abutted the home. We got the chimney demolished shortly before the new roofing. I looked at a photo I took of the home when all the old shingles had been removed and when I blew it up, I noticed that the wood around this area seems kind of dark. The black mold in the attic is occurring right below this spot. I’m guessing that there was some wood rot in the tongue and groove sheathing around the chimney area (perhaps from inadequate prior flashing around the chimney) and the roofers did not remove it. Perhaps the new roof work stirred up mold spores in the possibly rotted tongue and groove?

I’m really concerned about this, especially since if the original tongue and groove sheathing was rotten in this area, it has now been covered by a new plywood layer the roofers installed. It seems it will be difficult to assess the condition of the tongue and groove sheathing now that it’s been covered and it will be difficult to remedy. Any thoughts on why the mold has appeared and how to address the possible rot in the old sheathing that’s been covered?

Do you have soffit vents to provide intake? If so, are the soffit vents clear in the attic or covered with blown insulation? Without intake, the ridge vent is rather useless as you cannot create air flow in the attic space.

Also look to confirm the roof crew actually “cut in” the ridge vent. Some of the more shoddy contractors nail the ridge vent on without actually cutting a groove in the ridge rafters/beams.

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Hi. Thank you for your reply. The ridge vent was cut into the roof. Three smart vents were installed for in-flow on each side of the roof, about 2 1/2 feet from the roof edge. I checked and it does not look like the blown in insulation is covering them. I still wonder if this is part of the problem somehow, that maybe the smart vents are not working correctly for some reason. I’m hoping that the mold remediation company can advise me on this because I am certainly not an expert.

3 smart vents is only 9’, you need more intake.

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I agree with Axiom (As I normally do because he is normally correct with his input). Air is a fluid. Imagine the air flow from bottom of roof to top as water flow. The air flow is limited by the size of the tube (or intake vents). That’s fluid dynamics and physics, you can’t get around it. You may have 150 SF of output vent and it is wasted if you only have 9 SF of intake. You couldn’t efficiently fill your bathtub through a straw either.

Don’t look for much from the mold mediation people aside from possibly being able to give you an idea of the origin/cause of the mold. Don’t look for them to be roof ventilation experts.

Try a simple experiment. Go into your attic and go near where you have one of the “smart vents”. Blow some talcum power in the air and see what it does. If it does nothing more than settle to the floor and shows no indication of air movement, that should tell you what you need to know. Or light a cigarette and blow some smoke in the air. If you’re ventilation is performing properly, it should slowly but surely pull that smoke out the ridge vent.

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Is there any eave ventilation that was part of your system prior? If so the smart vents may just be acting as exhaust for the eave vents, leaving the upper portion basically unvented.

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Thank you for all the replies. It does seem that something obviously must be amiss with the ventilation. I will try the test suggested by Authentic_Dad, although I wonder if there would be any current if it was a still day outside with no breeze or wind? Regarding the amount of smart vents, the house is pretty small and I’m guessing that the roof peak (and therefore the ridge vent) is about 20-25 feet long, so 9 feet of smart vents per side would be 18 feet, so not quite as big a discrepancy in inflow vs. outflow. But I will investigate this further.

As Authentic_Dad stated, the mold remediation people are not ventilation experts and I certainly am not. They are coming on Friday of this week (a few days away) so I’ll have more info than. Assuming the mold company is not much help in this area, any suggestions on how to get an honest and accurate assessment of the ventilation and figure out what I have to do? Should I try to find another roofing company to come in and take a look? Or some kind of neutral inspector? I’m really concerned I might need to get the whole roof redone! Thanks again for all the assistance.

I wouldn’t panic. I seriously doubt you need to get the entire roof redone. It may have nothing to do with the ventilation, all this is speculation at this point. We have limited data to go on and can only guess at a few things. Hopefully the mold mitigation folks can determine the source of the moisture causing the mold. That should lead you to better determine a fix.

Thanks Authentic_Dad. Good reminder to pause, take a breath and get more information, and then decide where to go from there. I’ll post again after the mold remediation folks come in later this week. Thanks again to everyone for taking time to assist. This is a really great forum. Peace, Christopher

Hi. I wanted to follow up on my original post and ask two follow-up questions please. I’ve had two mold remediation companies come and inspect / give estimates. The analysis of the roofing situation from one of them who seemed very straight-forward and knowledgeable was that he thinks the ridge vent in the roof may not be providing adequate outflow - he said that the ridge beam or ridge board is probably restricting outflow of the ridge vent. The roofers who installed the ridge vent did kind of an uneven cut so the space left on each side of the ridge beam varies between about 1 inch and a half inch. I’m wondering if anyone has any thoughts on this. I assume that all houses have a ridge beam so ridge vents must be able to work well despite these?

The second question regards parts of original tongue and groove sheathing of the roof that have some rot on the upper side of the sheathing. When I got the new roofing job, they said they would inspect for problems like bad sheathing, but they did not tell me about these problems. The original sheathing was covered with a layer of 1/2 inch plywood and the roof was finished. Should the rotten parts of the original sheathing be somehow removed or extracted from under the new plywood layer? Or would it be okay to leave these, rely on the plywood layer and a new roof along with mold remediation for the mold on the undersides of the boards? If removal is recommended, is this going to be a difficult and expensive remedy because of the plywood and roof on top of it all?

Thank you for your thoughts. I hope some of the original members who answered my post first round will reply.

Ridge vent has to be installed according to specs or it will not be effective. It also needs to be cleaned periodically.

Original decking can not be extracted from underneath. Mold remediation can happen but any deck replacement will involve removing roofing and new sheathing to get at the bad wood underneath. Yes it is an expensive job, unfortunately. Hopefully you have recourse against the roofer or he agrees to come and fix it.

How was the roof ventilated before?

There really wasn’t much ventilation before - in fact, the only ventilation I know of was a smallish gable vent on the east and west sides of the home. It did not have any soffit venting or any other type of intake. That’s why I find it a little baffling that the mold showed up after roofing.