Inspected a home today and above the unheated garage on the East side of attic there was mold/mildew in a few areas, from lack of ventilation. No vents in the soffit. What I found interesting is the marks on the sheetrock as well as the roof sheathing. Normally I see insulation, even above the garage, so I do not know if this is normal or different?


Those whirly’s allow rain/snow in which is the water marks that you see.

I would say a roof leak below the “whirly” which may be leaking at the flashing of the penetration.

Sorry, I have to say no to both comments, no offense. The photo does not do the condition justice. The field roof vent is well above the marks on the sheathing/drywall and the condition appeared also where no vent or flashing were installed. Any other ideas?


Lets try this again, hopefully this is a different photo.


Flashing leak at the whirly, and leaked downstream and stain on the sheetrock below also.

Why would a garage need insulation unless you want to climatize the heated space?

It is not uncommon in this area to insulate the walls and not the attic.

You can get to the attic if you change your mind. The walls, you can’t.


I appreciate your input,however you could not be more wrong. There was no leak. The OSB was not that wet or damaged and the drywall was not damaged except for the markings. Also this same pattern appeared in about 8 locations (less severe) along the length of the wall line. The cause , I am certain was no soffit /eave vents. As to insulation or not, its not very relevant, just an observation, that I normally do not see garages with out at least a little insulation. Maybe the insulation estimator in this county is just really good at selling jobs? What I do see is plenty of poorly ventilated attics.

Its a leak ! It has to be because it drip down to the drywall.
Where else in the world could it have came from if not from a leak past or present.
Did you look for a nail pop ?

Turbine vent.
They can allow reversed atmospheric pressure.
The Louvers are only working when in rotation.

A clam day may allow rain to enter the openings between the bent louvers.
During high shear load the weather can penetrate the louvers opening as well.

It depends the angles of the wind.

That looks low slope. What was the pitch please.

Frost buildup in those areas during the winter due to high humidity in the attic. The first photo looks like a seam in between the plywood, which is probably one of the coldest spots in the winter. The stains you see are from the frost melting and then dripping down onto that area and saturating it.

And it doesn’t look like a turbine vent or a “Wirly”, it’s just a plain old square roof vent.

So why don’t you tell us what is going on?

No one here is “wrong” because you know or don’t know what your talking about…

We have an opinion, we can’t diagnose a situation from here. Matter of fact where the hell are you? Try filling out your profile.

Around here my bike get soaking wet out in the barn just because of temperature swings and relative humidity conditions. It would help to know where you are at and what information makes you feel you don’t have a leak instead of asking why you have water intrusion.

Do know what causes condensation?

There is no need for ventilation or insulation in a unconditioned garage. There is no humidity to control and there is no temperature to control between the outside and inside of an unconditioned space. You can increase ventilation and insulate all you want and the problem is not going to go away.

As a matter of fact, it will more than likely make the situation even worse!

Great deduction.
I thought the home was in FLA.
That was my first deduction Cam.

There is to much venting in the space. That bloody turbine is excessive IMO. The layout and roofing & interior components are part of the issues IMO.

All the best.

That home in a cold climate Crag.
As soon as I saw the staining that the eave and what appeared to be the deck sag between the trusses, snow load and frost was my first hypothesis.

He’s near Seattle.

Garage ceiling areas should not be insulated as they are not conditioned spaces…
Your market may vary…

[quote=“dandersen, post:11, topic:77788”]

So why don’t you tell us what is going on?

No one here is “wrong” because you know or don’t know what your talking about…

We have an opinion, we can’t diagnose a situation from here. Matter of fact where the hell are you? Try filling out your profile.


LOL :wink:

[quote=“mcyr, post:15, topic:77788”]


Screwy angle in the photo but to me, it looks like the “H” clip is missing at the location where two pieces of OSB roof sheathing butt up. The exposed edge of the lower panel can be clearly seen. When water seeps into such an area it will spread out in a circular pattern which would account for the stains on both sheets of OSB as well as directly below the open seam on the garage ceiling drywall. It probably does not leak every time it rains but when there is enough wind action to force water under the shingles. See this kind of thing here in FL all the time. After Hurricane Ivan, a particularly nasty Cat 4 we had in 2004, I saw numerous homes where the wind action was so severe that most of the H clips had been popped out and sheathing actually moved leaving gaps between the sheets of OSB and plywood.

Happen to have this one from that time, on my external hard drive. This one still has the clip in place, but found dozens of homes with much of the sheathing gapped like this after the storm. All had to be stripped off and replaced.

2203 Frontera St 040.JPG

Ok, ok, no one is wrong. A very poor choice of a word. To answer a few questions…I am and the home is in Sequim WA. We are in a rain shadow of the Olympic Mountains and receive about 17 inches of rain a year, but this home is only about 1.5 miles from the Straight of Juan Da Fuca, or simply the Pacific Ocean. We have very little snow or frost. The vent is a plain old Roof jack, no 'Whirly"Turbine. The pitch is 4/12. And I checked for nail pops, paint peeling (on ceiling) and probed the drywall from the attic (it was not easy, tight fit) The sheathing may have been pushed down, because when I was on the roof (always start Inspec. outside) I noticed the soft sheathing in that area. In this area, (lots of retired folk, who putter in the man cave) the garage lid is often insulated, in fact more often than not. That is what started this thread, as I have seen lots and lots of mold/mildew on sheathing but never observed the whirly mold/mildew marks on the drywall. This may only be because most attics (even garage) are insulated and the markings are not clearly observable. Thank you for the input. If it makes any difference my 12 year old daughter told I was grouchy this morning also. “I mean like really Dad, what a grouch”

If it’s not cold enough for frost, then these other guys are right. It’s a leak from some other time(and dry now), but the nature of the leak is the real question.

You may not know this for sure(unless maybe you have a photo of the roof?), but did any of the seams in the shingles line up? This could allow leakage at a much lower joint in the roof decking and not look like there was a problem at all with the roof.