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Most likely caused by improper attic ventulation. I don't know if the black stuff is "mold" or just the color plywood turns after years exposure to moisture trapped in the attic. I see a date satmp on the OSB Sept 11 of the side wall - is this house that new? Can you describe the ventulation setup.

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Hello, the OSB is the sheathing which was placed under the new Hardie Board a few months ago. The House was built in 89 an had T1-11 and LP1 siding which was stripped. There was no backing behind the T1-11.

The attic has 6 sofit vents on one side and 3 on the opposite. In addition, it has two gable vents. No roof vents.

Thanks!

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Also the roof was replaced in 2008 prior to closing. The roofer stated the sheathing looked good from the roof side. Looking back I wish he would have just replaced it all but the previous owner foot the bill on that one.

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I see this type of staining all of the time with older plywood sheathing and as Mark stated, it's usually caused by poor ventilation. Be sure those soffit vents are clear(baffled) and the ridge vents(cans) are installed properly. All the roofers typically do is walk the roof and if it doesn't feel "soft", it's all good. If I were the owner, I would have replaced the sheathing same time as the shingles.

BTW, I see in the first two pics that there is insulation blocking the soffit vents...

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I had one that had the same look. It had blocked soffit vents, very few(partially blocked) roof vents and two bath vents with no ducting (which is "ok" [:-thumbd]). The decking had been replaced along with the shingles only about 10 years ago. The moisture damage was visible from OUTSIDE!

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That's cellulose insulation. Properly installed cells has virtually the same air sealing properties as spray foam. Look for big holes in the insulation and bath fans or drier vents that exhaust into the attic. Seal and insulate the attic hatch, and lower the humidity level in the living space. Then install a properly sized ventilation system.

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Observation, but cellulose is like anything else. You get what you pay for.

We use the same cells for loose fill, dense pack, and new work. I would imagine the glue in it contributes to the air sealing properties, humidity activates the glue and the density clamps it in place until it dries. We're also using lots of material, R49 is 16" loose/14.5" settled.

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Hi,

Number 1 - Stop calling it "mold," whatever it is, it's fungi of some sort. When you say mold you automatically trigger my BS meter, because the whole "toxic mold" thing is B.S.

Number 2 - Make sure that every exhaust fan is venting all the way outside via a connected and dedicated rain cap that has a male extension that comes through the roof plane - if there is a flex duct lying on the floor of the attic aimed at the eave vents or hanging by a piece of wire just inside the gable end vents it is really venting air into the attic and is unsatisfactory.

Number 3 - Add vents near the crest of the roof. They typically use pot vents around here but a ridge vent will pull more air. Regardless, a ridge vent or pot vents combined with gable end vents is going to pull air from the gable end vents instead of the eaves and won't dry the underside of the roof very well - ergo, the fungi. You're profile says you're in Seattle; so, unless you've got a real oddball house, you don't have soffits, you've got deep overhanging eaves. It looks like the builder did what so many around here do; he drilled under-eave vents at every third rafter bay instead of every rafter bay. Close the gable end vents and make sure there is free flow of air through every rafter bay from eaves to ridge. That means installing baffles between rafters and drilling eave vents through the frieze blocking in the 66% of rafter bays that don't have them.

Number 4 - Treat the fungi with a fungicide such as TimBor, BoraCare, Concrobium or similar to kill it. Wood Care Systems in Kirkland has what you need.

Number 5 - If you're concerned about the staining inhibiting future sale, clean the underside of the roof. Some companies send a group of peons up into the attic with buckets, pieces of plywood to lie on and scrub brushes. I think it makes more sense to use a portable soda blaster with sodium bicarb. It will leave the wood all pretty. Once it's scoured, coat it with some BoraCare and you'll be in good shape. Don't worry about the bicarb and residue landing on the cells - the cells is totally infused with borate so it won't burn and borate is toxic to fungi so it's going to die when it comes into contact with the cells.

Number 6 - Go on with your life and stop giving credence to media fairy tales about toxic mold.

ONE TEAM - ONE FIGHT!!!

Mike

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Thanks for all the information all! Resale is a concern and I certainly do not want this to become worse over time. After reading the comments I am leaning towards hiring to add more ventilation and clean/disenfect the sheathing. The bathroom vents are ran to the same location just under a cap. They are not connected in anyway and fall short of actually exiting the roof by approximately 2 or 3 inches.

You are correct sir, overhanging eaves. I looked last night and I have 3 open on one side and 5 on the opposite. The insulation is not blocking any of them although it appears the cardboard baffles could be re-situated to allow more air flow.

On the second part of the house there is 14 feet ceilings. I imagine there is no more than 24 inches of roof space between the inside and outside. I think I may install roof vents there as well even though I cannot see inside the cavity.

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You might have scissor trusses. It's not uncommon around here to find an 80's house with scissor trusses above some raised ceilings. What style house - do you have a picture?

ONE TEAM - ONE FIGHT!!!

Mike

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These pictures are from the listing in 2008. The roof was replaced later that fall just before closing. What now amazes me it it appears from this photo roof vents existed. They are sure not there any more. It amazes me to think they would have been taken out and roofed right over. I did notice at least one place in the attice that has a hole approx 18" by 18" that had been covered with metal and shingled over. Perhaps the previous owners saved a few dollars by not reinstalling them?

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I'm surprised there isn't a wall hatch in a closet somewhere on the second floor to access that area. I did a similar design last week where a built-in bookcase in an upstairs closet had to be removed in order to unscrew an access panel and enter that area.

ONE TEAM - ONE FIGHT!!!

Mike

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Mike,

Nope, two bedroom walls and open stairwell area border that portion. I wanted to look into the area when the siding was stripped but the contrators had the wall all buttoned up before I returned. I cannot imagine re-insatlling the vents there harmful.

Thanks for all the input you do here!

Jay

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  • 5 months later...

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