1. Myth #9: Insulation is insulation--- does not matter what kind.
We could spend hours talking about insulation, but we have to understand how insulation can affect ventilation. A roof structure with insulation that has great air sealing abilities will be less adversely affected than a roof structure with insulation that has poor air sealing abilities.

2. Non-Encapsulated Fiberglass Insulation
This is an insulated wall between a crawl space and a space above a basement ceiling.
The black discoloration is where air is being “filtered” by the fiberglass insulation.
This filtering can be seen on both sides of the insulation from air “exfiltration” and “infiltration.”
Insulation materials that are also a good air barrier do not have this problem.
For fiberglass to be fully functional, it must be encapsulated and air sealed on all six sides. If you cannot achieve this (and it is not very easy to do), it is better to use some other kind of insulation.
Many people are becoming aware of the importance of covering fiberglass on 6 sides to make it as effective of an insulator as possible, but it is perhaps just as important the six sided enclosure also be air tight.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

3. Picture courtesy of Charles Buell---Charles Buell Inspections, Inc.
Insulation not air sealed
Insulation not air sealed:
While I am a huge fan of cellulose fiber, it too has to be of sufficient depth to be an effective air barrier. 6 to 8 inches is typically adequate.
This is a very thin layer of spray cellulose at one location where it is less than an inch thick--it too acts as a filter. The dark ghosting (highlighted grey) from top to bottom at the right side of the picture shows this filtering.
Picture courtesy of Charles Buell---Charles Buell Inspections, Inc.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

4. Adequate Air Sealing IS Possible
Adequate Air Sealing IS Possible---and at Acceptable Cost:
This is the attic of a house I built in 1983 in Skaneateles, NY--as seen in inches of blown cellulose is installed.
No moisture staining was noted.
The white 3-tab roof was replaced after 30 years.
The roof was originally installed with no felts—no underlayment.
I know, crazy, right? It was an idea going around at the time--kind of like the flu.
It was with great dread that I visited this house after 33 years.
Adequate Air Sealing IS Possible
At Acceptable Cost
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

5. Picture courtesy of Charles Buell---Charles Buell Inspections, Inc.
As you can see, the roof behaved itself just fine--zero evidence of ice-dams in an area prone to ice dams.
My first reaction to the owner when he showed me this picture was, “Nice job replacing the sheathing!”
He laughed and said, “No, that is YOUR sheathing.”
Anyone that has replaced a lot of shingle roofs installed over felt paper will note the black “signature staining” of the felt paper on the plywood is missing.
This house is an example of what good air sealing will do for you. The octagon roof had marginal ventilation by current standards--or any standards. 2” louvered strip-vent is installed all around the perimeter and 8 can vents at the peak of the roof. (3 of these vent locations were used for exhaust fan terminations—leaving five for attic ventilation.)
The venting added up to 14+ square feet NFA at the soffit vents and 2+ sq feet of NFA at the top.
This attic space should be considered WAY under ventilated, but certainly pressurized. 85% of venting is down low and 15 percent is up high.
Given how long the 3-tab roof lasted, and the lack of moisture issues in the attic, are we really going to recommend additional venting be installed?
Could they have gotten another 10 years out of the shingles? Keep in mind these were year shingles to begin with.
Picture courtesy of Charles Buell---Charles Buell Inspections, Inc.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

6. This is what houses should look like in cold uninhabitable places in the winter.
Tons of snow on the roof, NO ice dams and NO icicles.
How much do you think this 34 year old attic cares about “ventilation?”
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

7. Skylights not air-sealed
Incomplete air barrier around the skylight/skylight well--allows warm moist house air to leak into the attic.
In the winter, the dark stained areas might be white with frost if you were lucky enough to be there at the right time.
It could also show up as frost during periods of night sky radiational cooling.
Skylights not air-sealed
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

8. Whole house fans
Whole house exhaust fan.
Does anyone care to venture a guess as to how much soffit venting and roof venting it takes to keep from pressurizing the attic with one of these things? Of course it is going to vary with the CFM of the unit, but the one in the picture requires 10 sq ft of NFA---that is one dang big hole!
Previously we discussed that the attic is almost always under negative pressure in relation to the house interior. This is one way to make it radically worse.
When you find one of these, do you check to see if additional soffit and roof vents have been installed?
And how does that venting compromise what is required for keeping the attic cool?
These units simply sucks massive amounts of air out of the house and shoves it into the attic where it then tries to get out.
There is no insulated cover for this unit either---so how much heat is lost to the attic in the winter with no insulated cover?
The idea of these is not “terrible” and they can actually be used effectively to pull all the warm air out of the house to cool the house at night and thereby reducing cooling loads during the day.
In the Northwest I just want to see them go away when I find them.
I think in climates where the average night time temperature is 20 or 30 degrees lower than day time temperatures, a unit like this could pretty much eliminate the need for air conditioning in a well insulated and well air sealed house. However one should probably choose carefully, as one of these in conjunction with a house that has an air conditioner would likely only make things worse.
Copyright Carson Dunlop & Associates, all rights reserved. This content may not be reproduced without the express written permission of the publisher, Dearborn Home Inspection.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

9. Attic Power Vents
Attic Power Vents:
This is similar but different.
This fan has been installed for only one purpose--to increase attic ventilation.
Again, is sufficient additional soffit venting being installed to prevent depressurization of the attic?
Doubtful.
These fans will always get a recommendation for removal from me in this area.
The wiring is also a little less than professional.
If the house itself is overheating, is it because of lack of ventilation or inadequate insulation?
So what happens if we attempt to increase ventilation with an attic power vent?
We will likely increase to some extent the amount of moist air entering the attic thus increasing the opportunity for humid air to find cold ductwork.
We will likely put the ceiling under negative pressure and draw conditioned air into the attic space. We will also draw conditioned air (increase the leakage) of the ductwork that is in the attic. The amount this cold dry air will lower humidity and temp in the attic is likely minimal but the bigger factor is the increased inefficiency of the HVAC system as it has to deal with the additional warm moist air being pulled into the conditioned space from wherever it can pull it.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

10. Picture courtesy of Jim Quarello, JRV Home Inspection Services, Llc.
Something else happens when we move more air though the attic.
The amount of dirt in the air that can be collected in the screens of the vent intakes increases.
This picture is a great example of that collection---and the smaller the screening the quicker it will clog.
Picture courtesy of Jim Quarello, JRV Home Inspection Services, Llc.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

11. Framing Bypasses
Framing Bypasses:
Gaps in framing are common.
This opening never got properly covered and now there is no insulation covering it either.
These gaps are fire-blocking issues as well as energy efficiency and building performance issues.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

12. The view down the breach of the previous picture.
All of these walls are like “radiators” for heating the attic--assisted by air leakage around all the boxes cut into the walls as well as a chase where cold air can drop out of the attic.
Once again convective loops take over to make this an energy waster 24/7/365--whether heating or cooling.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

13. Openings around tub drains
Openings exposed in crawl spaces is another very common way crawl space air is drawn into the home.
It is not uncommon to see the insulation in this area, if it is fiberglass, stained dark from air movement through the insulation.
These kinds of breaches need to be air sealed with materials that can actually accomplish the job.
Openings around tub drains
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

14. Plumbing Pipe bypass Wiring hole bypass
Pipe and Wire Openings
Where pipes and wires pass through framing top and bottom plates, any openings should be properly sealed against air movement.
Wiring hole bypass
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

15. Holes for Wiring
Openings like this can allow a lot of conditioned air into the attic.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

16. Plumbing Pipe penetrations
Openings around pipes must be sealed
Plumbing Pipe penetrations
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

17. Top & Bottom Plate Shrinkage
While uniform shrinkage will not result in a uniform gap, some amount of gapping will occur.
It happens on exterior walls as well, and if fiberglass is installed in the walls the air will still find its way to the attic space.
This is perhaps the most commonly overlooked air bypass--all the lineal feet of exterior and interior walls of the home.
How much gap there will be depends on how much shrinkage and of course a 2x6 wall shrinks more than a 2x4 wall. However with the 2x4 wall it is on both sides. All of this occurs at both top and bottom making every single wall cavity a little chimney carrying conditioned air to the attic space. Again this will be occurring 24/7/365.
In new construction this is fairly straightforward to deal with before insulation is installed.
When upgrading insulation in older homes, any previous insulation would need to be removed to accomplish this air sealing.
Of course if all drywall was installed with continuous bead adhesive—just imagine how much better air sealing we could achieve.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc

18. This is an example of the areas where shrinkage can occur resulting in bypasses into the attic.
A 2 bedroom, 1 bath, 1200 sq ft house can have 400 lineal ft of these kinds of gaps (both interior and exterior walls).
Even at 1/128th of an inch gap it would add up to about 36 square inches of openings. A 6 inch by 6 inch hole.
Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc