Winter attic mold

We live in the Pacific Northwest, western Washington. When we purchased the house 8 years ago there was mold in the attic along with a metal roof and metal ridge vent.
2.5 years ago we had the

  1. roofing replaced with shingles;
  2. Removed old insulation
  3. New cdx plywood for new roof
  4. Installed a certainteed baffled ridge vent 9” with filter fabric (Aka shingle vent 2)
  5. Dry ice blasted the remaining mold
  6. Installed new insulation - rock wool
  7. Installed styrofoam baffles.
  8. We also airsealed the attic floor , along with the can lights.
  9. The bathroom vents vent out the gable wall. The ducts are insulated

I started seeing high humidity when fall came in and we had to turn on the furnace. So I had my roofer cut the wood between the bird blocks To expand the space and put up new screen mesh since some of the old mesh was painted over.
I calculated the nfa of the mesh and it’s 66%. So based on rough estimate of the sizes of the holes, I would have 1/150 or more intake vent.

Mold appeared shortly after that mostly near the eaves. Some were away from the eaves and I pulled up the rock wool to find some small gaps that were letting air through. I sealed them. Even a tiny gap was causing extra moisture resulting in mold.
With the mold near the eaves, maybe there are small airleaks from above the top plate? I foam sealed the baffle to the top plate already but still seeing the mold.
I even experimented putting fans near on the ridge to help move the air. I think that made things worse so I disconnected the fans.
what am I missing? Maybe I don’t have enough intake? The entire roof has ice and water shield … does that make a difference? Is my ridge vent gap wide enough? Is the filter in the ridge vent inhibiting the flow? I have an addition that has no ridge board in the middle but the rest of the attic has a ridge board. The gaps by the ridge board is 1/2”-3/4” wide on each side. Maybe the 1/2” is too small?

Thanks for reading and your thoughts on this!

Here are more photos

This is looking into the new addition that is above the big garage. The old gable wall is still there but with a hole cut in.

We barely get sun in the winter. This photo is from late spring.

This isn’t a reflective shingle is it? A lot of reflective shingles backfire in the winter, especially on North sides and roofs with limited sun exposure. And yes, full ice/water can be a problem in our area but usually not with the ventilation system you have.

It is the marlarky Windsor. Don’t think it is reflective shingle.

No it isn’t. Ivoman or Dark Thirty will have to weigh in.

My first instinct is that the ridge vent holes are not wide enough.
They did it fine where there is no ridge board
But im afraid its too small where there is if you are correct in the size of those air gaps.
I like a total of 3 inches air gap at the ridge.

Would it be sensibe to identify your “true concern” and address that first? What exactly is the “problem” you are trying to fix?

Is it simply the mold?
Is it the risk of illness?
Is it wood rot from mold?

If it’s the mold itself, good luck with that because mold is everywhere and your climate is notorious for high humdity. The new plywood is ideal for mold/mildew to take hold and there is oodles of raw plywood for it to do so. I’ll guarantee there is mold residing in hidden areas as well. Chasing it all down will lead you to germophobe insanity! Have you considered treating the underside of the plywood to deter growth? Maybe try spoiling the milk?

If your concern is health, test the air inside the living area to see if a looming health concern exists. You’ll likely detect some ambient mold spores and maybe an “in home” Hepa filter will be the simple answer to improve air quality to an acceptable level for your personal well being? A mold remediation company will certainly detect more harmful mold than an independent testing lab not selling filters or mold removal services.

If your concern is structural, have the mold tested to learn if it is the kind known to rot the wood. Most white molds will not destroy wood but … who knows, your’s may be one of the “unusual suspects?”

What has been accomplished with your ventilation, insulation and such, seems to be a picture of perfection. This is textbook stuff in my mind. Will you work on contract? :wink:

If all else fails, move to a dryer climate where spiders are a problem.

Good luck.


Thanks roof_lover! Do you think I can cut the plywood wider from the attic side with some tools? Or can it only be done from the top side? If only from the top side can the ridge vent be reused? If not, should I use a better one than the one I have? I was watching a video from lomanco on their Omni ridge vent vs shingle vent 2 and other vents when put above a clear plastic smoke house to see how the smoke was escaping the attic. It looks like the Omni did a better job. Maybe I should have that on my roof instead?
Here’s the video:

Thanks Ivoman! Our previous roof attic had mold when we moved it. We made some repairs to get rid of adding moisture to the attic like venting the bathroom fan out the gable instead of into the attic. Then I didn’t think much about the attic. But over the years the mold continued to take over and our health declined. Especially my newborn. We went through a lot to fix our attic and roof so we can stay in this house. Many homes in this area are not that great and to move just means having another home to fix up again.
Our healths improved after the new roof and mold remediation . We do not want to go through that again where the mold take over the attic and ruin our health after spending tens of thousands on the new roof and all that went along with it. If it’s the roof installer who did something wrong or the product is not workiNg right with the home then I want that addressed.

Thanks for the compliment. Another contractor said the same thing to me. I’m a petite woman so I can squeeze into small spaces to work… like the narrow attic eave area. My roof is 4/12. It’s hard work and I only plan to work on my house only.

I was also thinking of cutting or totally removing the filter mesh … maybe it is slowing down the exhaust?

Spray this, or another similar product, on the exposed plywood and trusses.

“Spoil the milk”.

I’ve seen mold grow right through or back on top of that paint. Trust me if there was a product that can keep mold away I would use it. I’ve found such one and have used it on the smaller attic sheathing and it worked! But that company is no longer existing…

Other tidbits: I put a smoke pencil by the eave in the attic and the air does move towards the ridge slowly. This was the winter time.
In the summer the attic gets at least 120F or higher.

I would agree with Ivoman. Im not in your area so im just putting out an idea. Ive done many attics with Heatbloc Ultra. LowE coatings block 80% of the radiant heat. In Texas the shingles heat and that heat transfers to the cooler attic. The coating limits the passive heat. Your problem may be what ivoman says, humidity. Heatbloc doesnt have mildew resistance in it, but you might call them or shoot an email. Kemper sells it through STSCOATINGS. An airless sprayer is needed. Its waterbased, but its a tough job for a DIYer, but not impossible.

If you cut the mesh your attic will be infested with bugs and you may also add moisture from the outside as well due to wind driven rain.

@Tileman i hear that the filter mesh gets clogged up over time with debris and bugs and that would reduce the air flow. Is that your experience as well?

Thanks but I want the exterior heat in the winter to dry out the sheathing . And I don’t want the heat in the summer…