Ventilation in attic

I found these signs in an attic today. Stains on the insulation and rusty nails above the stains in the roof sheathing. Is this a sign of poor ventilation in the winter?


These nails are rusting due to the living area heat breaching up through the ceilings and into the attic cavities during the winter months from inadequate insulation depths. This heat loss causes an ice build up on the hardware and it will eventually melt and drip.

Massachusetts requires R-39 value.

Ventilation could also be a contributing factor if insulation is adequate.

Dave, how is heat causing ice buildup?
Since it looks like all the nails are rusted, it looks like high humidity to me. I’d say moisture from the house rising into the attic with heat.

Check bathroom exhaust terminations carefully which you see this condition. Here’s one I dug up.



I see this daily in the winter months.

Please don’t insinuate that I’m wrong.

The bathroom exhaust fans terminate in the attic. Here is another photo of the sheet rock, this area is framed for a whole house fan there is no insulation in this area.

You answered your own question Buck…the bathroom exhaust fans terminate in the attic…there is your moisture Sir…or at least a significant part of it…imo…

The drip stains (on the exposed drywall) only indicates that the heat escaping from below this uninsulated cavity is causing excessive dripping from the frost build-up on the roofing nails.

I agree with you Dave on this one, see it all the time up here.

Excessive heat loss due to poor insulation and poor ventilation to keep the attic cold and suplemented with bathroom exhaust vented in the attic can form frozen condensation on the underside of roof sheathing up to 1/4" thick in some cases.
When the sun comes out for a while and temperature rises, it starts dripping and once dry, the sheathing shows the signs of rust from the nails.


Thanks! for the help.

Yes, but it is a dry heat. :smiley:

I wonder where the frost on the nails comes from. :cool:


The winter months.

I’m not following you. Where, during the winter months, does the moisture for the frost on the nails come from?


Refer to my post#2

That gets us back to my post # 10.

The ***moisture ***is coming from somewhere.

How do you know the roof isn’t shot and chronically leaking at the nails?

If it is not vented correctly than it is what David said.

Although you can be wrong just like the rest of us… my impression of you is that you’re a top notch inspector and I have a lot of respect for your opinions.
I didn’t understand your opinion from your post, and so my post was asking you to explain more clearly. It was meant as an attempt for me to to understand, not an insinuation that you were wrong.
Then I added my thought to the post.

I’m thinking that having that tapeworm fogged your mind and that’s why you misunderstood my post. Thank god my remedy worked!

Are we good now? You’re not mad at me are you?


We’re good. I just thought I was being challenged on my statement. I see icing on a daily basis (in the winter months) and I simply base my opinions on my experience.

Let me reiterate. We already know that humidity (which is moist air) causes icing of roofing nails inside the attic cavity.

All I’m saying is that any heat loss (which is also moist air) from inadequate insulation will inevitably leak into an attic space and condense on the exposed cold nail tips, causing ice to build-up on these nails due to temperature change.

Now…when these frozen nail tips change temperature again (from daytime sunlight conduction) the ice that is built-up on these nails will now thaw and will drip onto the insulation and ceilings below them.

Here’s a good article that’ll back me up…,,20248142,00.html

This may help also David;

Attic Ventilation Problems

Attic ventilation requirements are usually specified in local building codes, and in many cases these requirements are followed during new house construction. Ridge vents, soffit vents, or gable vents are some of the methods used to provide for attic ventilation. There are also power ventilators that can be installed to supplement poor ventilation. Proper attic ventilation requires air to move in an upward direction of travel. The problems occur when insulation is stuffed into the soffit area closing off the vents, The ridge vent is installed, but the roof was never cut sufficiently to allow proper air flow to occur, or incorrect vents are installed that permit air to flow, but do not remove the air from top to bottom such as installing gable style vents and ridge vents without soffit venting. These ventilation problems allow for insufficient air flow. During the winter months heat rises from your living space into the attic space causing a warm on cold condition to occur that results in condensation on roof rafters or trusses and the roof sheathing material. When the temperature is extremely cold you may even find ice or icicles in your attic. This leads to the next problem.

Poorly Installed or Insufficient Attic Insulation

Insufficient insulation allows excess warm air to travel upwards into the attic, instead of being kept in your living space, this not only allows condensation to occur, but dramatically affects your energy cost. In the summer months just the opposite can occur, and you may even have condensation that occurs in the living spaces near the ceiling areas. Building codes provide the proper type and R value necessary to reduce this heat loss. The old saying “That more is not always better” is the next problem, many times homeowners will have additional insulation added, unfortunately this can turn an attic that had good ventilation into one that now has poor or no ventilation. Typically when this situation occurs the insulation whether it be blown in or batted is fitted incorrectly and shuts off the vents located in the soffit area of the house. Many times even the vent chutes used to allow air to flow into the attic are crushed or completely covered rendering them useless.

Incorrect Venting of Bath Fans and Dryers

This problem should be very self explanatory, hot steamy air is pumped into the attic causing an excess moisture problem. Many times home owners don’t even know that these item are not vented correctly. They should be vented through the gable end or out through the roof. We commonly see these vents stuffed out near the soffit area, occasionally this works, but more then likely the hot steamy air never makes it to the outdoors.


Thank you, David.

That is where I was going, too…humidity.

Appreciate the clarification.