I am looking for any studies or research on vented soffits. 

And, what is your opinion on the age old practice of venting a soffit?

I personally am not sold on the idea and would look to a more controlled method of extracting moisture out of an unconditioned space. Or just spray foam the underside of the roof sheeting, or scissor truss w/ raised heal and BIB it. 

Tags: managment, moisture

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What climate zone are you in?


Im asking as my old company has gone to spray foaming the underside of the roof sheeting to the soffit that is blocked off.  They havent done a vented soffit in a while.

But I did a side project for a relative who needed a roof redone and we found lots of sheeting was rotten and needed 75% of it replaced. The house only had vents in the top of the gabled ends. So we added lower soffit vents per code and full ridge vents.

Just brought the ? of on new construction just to forgo a vented attic space.

The actual research is limited to some work by Frank Rowley at the University of Minnesota in the late 1930's regarding ventilating attics to eliminate ice dams.  WWII interupted the research and the 1942 wartime FHA houseing guidelines picked up some of his figures for the 1:300 ratio on attic ventilation.

Now we have a code that says 1:300 with high vents only. And 1:150 if we use at least 50% low with the high.

Soffit Vents are easy to install and the only complication is baffle.  It has been since the '50's around here that a new home has been built without eves.  My mid '60's home has no soffit baffles.  Just gable ends.  I added roof vents the last time time I re-roofed. 

Low and high is good.  You can use eyebrow vents to match the roof vents or the ridge vent.  The most important issue to enough net free area.  

Soffit and roof are easy and simple, so most people just assume you have to.  

Low and high allows less NFA to accomplish the same thing.

Rowley's work is cited in Wm Rose  Water in Buildings Univ of Illinois Press

Other research of interest was done by the American Roofing Council.  They were looking at factors that reduced shingle life.  So they measure shingle temperature as a proxy.  Miami, Minneapolis, Boston, San Diego, Baltimore, KC, Phoenix and another city.   North Slope, South Slope; Light color, dark color; Southern or Northern location, ventilated V unventilated attics.

Ventilated to Unventilated was the smallest temperature change in the same city. About 2 degrees.

Here is a a little something on the subject matter, hope it helps.


Thats a well written article. Thanks!

No Problem!

Building Science Corp. BSD-102: Understanding Attic Ventilation



Asphalt Roofing Manufacturers Association



I’m in Canada!  Ventilation, the removal of both heat and moisture from the roof space is paramount and we super ventilate attempting to remove as much heat and associated moisture in all seasons preventing mold and decomposition of the structure and prolonging the Life of an installed sloped roof shingle as much as 50%.

Just a couple of quick thoughts

I love Hot Roof systems, but vented also works fine - the catch is the install on both has to be done right especially as you get farther & farther north (or into colder areas). For a simple ranch house vented is generally the easiest way to go especially with raised heel trusses. When you start getting into more complicated systems, foam becomes a better & sometimes even cheaper option.

If you are in an area that is listed as 50 PSF of snow or more you would need a modified system where you vent above the sheathing.

BIB - definitely no open cell here unless you are going 4" or more & based off recent pieces that notion is getting ripped some. Do not use batts, it should be a dense packed or other type of blown in system.

If you do use foam, it should cover the exposed wood on the top chords by at least 2" for CC

Finally no matter what system you need to keep the moisture from getting into the attic or a way to extract it. You really cant extract with vented (yes even with more venting) so you have to spend more time air sealing, etc...

Vented attics is the best way to go unless you put the mechanicals in the attic, then an unvented attic is needed. You can get more information on www.buildingscience.com

Someone sent me this link to a great Joe video. Answered all my questions! Joe for President, oh wait he's Canadian. 

And thanks everyone for the links and info.


oh and facia vents I have never seen before but make lots of sense once I saw a diagram. Kept thinking to myself isnt all that rain and snow just going to get blown in the attic by the wind. Opps I was thinking of a vent on the face of the facia not behind it.


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