1. Photo courtesy of Don Hester, NCW Home Inspections, LLC
A real-life story of how this works happened to a client of a house I inspected and I got the call 6 months later. 
(Don’t you hate those calls where the caller says, “You inspected my home about………” They do not even have to go any further before you are asking yourself, “Ruh Roh, what did I miss?” While it always ends up closer to: “And now we would like you to inspect another property for us,” it does not minimize that initial reaction.)
My client complained that he was not able to keep the humidity in the home high enough in the winter to protect some very expensive guitars. 
I suggested that he correct the missing weather-stripping on the attic access hatch (in the report) and close the upper window air intakes (also in the report). 
Humidity levels quickly returned to normal levels and the guitars are now happy.
Donnie’s Guitar
Photo courtesy of Don Hester, NCW Home Inspections, LLC
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

2. But maybe not IN the car! Go Ahead------try this at home!
Here is another example: (Keep in mind this might be considered use of an “electronic device” in a vehicle in WA State)
As you can see it is humid enough in the car that the windshield is fogging over.
It is 66 degrees F at 72.5% humidity.
Do I turn on the fan to clear the window?
Of course not, because I want to demonstrate how I can clear the fog by opening the window and letting cold even more humid air into the car.
But maybe not IN the car!
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

3. In this picture I have opened the window and after just a few seconds the fog is gone and we can see the humidity has dropped to 62.6% with no real change in temperature.
Your mind wants to go to a place that is logical, which might be to conclude the outdoor humidity has to obviously be lower.
But the mind does not always go where it needs to go to get at the truth.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

4. MAGIC!
As you can see, the outdoor humidity is 80.7% while the temperature outside the car is 57 degrees F.
This is some serious Magic.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

5. Disconnected exhaust ducts
A bathroom exhaust vent with no pipe to exterior--well it has one--it is just not connected.
This was new construction.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

6. Nice duct--just not functional
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

7. Dryers venting into attics can contribute a lot of moisture to the attic and is a poor way to add insulation to the attic.
It could even be considered a fire hazard.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

8. Inadequate termination to exterior
Two vents sharing one roof vent
Notice that not all of the air is venting out through the screened cap. This is consistent with a plugged screen or other restrictions providing enough resistance that air is bypassing the flange and entering the attic.
You may remember the previous slide of the exterior view of this. These roof vent caps have screens in them and there is no practical way to clean the screens.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

9. Air sealing that is not yet commonly on the builder’s radar
This presentation is no where near being up to the task of discussing all the guidelines for proper installation of roof ventilation systems, but I do want to talk about one particular thing that, if not done properly, can result in problems.
Many inspectors are not aware of this yet.
Most builders certainly are not aware of it.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

10. The attic is seemingly well insulated, with evenly distributed 18 inches of white fluffy, and yet there are still areas of cold ceiling all around the eaves.
Why?
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

11. This is a thermal image of air getting under/through the insulation along the perimeter of an exterior wall of a home insulated to modern standards.
(Note: in the summer the colors would reverse.)
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

12. Picture courtesy of Charles Buell---Charles Buell Inspections, Inc.
Desired flow of air from the soffits above the insulation baffle
The blue dotted line represents the path air “should” flow above the insulation in the space provided by the insulation baffle.
Picture courtesy of Charles Buell---Charles Buell Inspections, Inc.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

13. But what can happen if the baffle is not sealed at the vent opening?
Wintertime air flow
Summertime air flow

14. Raised Heel Trusses R-50 Cellulose
Obviously the best solution to this problem is to use raised heel trusses, and eliminate the need for insulation baffles.
For the life of me I have no clue why this idea has not taken hold. I was using them in 1976, so they are nothing new.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

15. Photo courtesy of Steve Howard
To correct this condition with regular trusses, the gap between the baffle and the top plate must be effectively sealed.
Photo courtesy of Steve Howard
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

16. Cut the cheese Honey—I’m comin’ home!
This is trampled/compressed insulation from vermin activity as opposed to air infiltration under and through the insulation.
The round “warmer’ area near the corner is nesting rodents---where “Honey” is home, cutting the cheese!
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc