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sandyman720 01-17-2008 07:17 PM

Is ridge and gable vent compatible? no soffits
Hello-I am thinking about getting a roof job (tear off to rafters).

They are adding a cobra ridge vent and I have existing gable vents. I do not have soffits.

Will this cause a problem or is it ok?

Ed the Roofer 01-17-2008 10:50 PM

Didn't you just have your roof done in August or September of this past year?

I remember discussing these things and your questions about how certain things were getting installed.

Whats up?


sandyman720 01-18-2008 05:27 AM

Hi Ed,
No this past summer I built an addition and therefore the questions were about that roof. It was a shed type roof.

See pics of my adventures building the addition here.....I did everything myself except hire someone to wrap the aluminum and soffit and finish the drywall.

I am going to have someone re roof the rest of the house. The original part of the house was built in 1950 and there are no soffits.

What are your thoughts on the gable and ridge? From what I am reading it will be counteractive.

NateHanson 01-18-2008 06:12 AM

Nice Work!!

XSleeper 01-18-2008 06:51 AM

Articles by experts in this field say no, they are not compatable. When gable vents are subjected to strong straightline winds, they can create a downdraft through the ridge, potentially pulling rain or snow down into the ridge vent.

Ed the Roofer 01-18-2008 10:37 AM


Originally Posted by XSleeper (Post 89554)
Articles by experts in this field say no, they are not compatable. When gable vents are subjected to strong straightline winds, they can create a downdraft through the ridge, potentially pulling rain or snow down into the ridge vent.

And likewise, since there are no soffit vents for fresh air intake, the side wall gable vents will coincidentally act as the intake vent portals for the ridge vent exhaust. When this occurs, and if their is inclement weather, this force will draw the exterior rain or snow along with the air into the gable vents and therefor potentially create leakage into the interior of the attic.

I have a report about a study on this that I will post a link to later.


Ed the Roofer 01-18-2008 06:10 PM

Here is an excerpt from that report I mentioned.

Here is the link to the entire paper, which is about 53 pages long.:


"Considering particular ventilation strategies, the combination of continuous ridge and
soffit vents is generally accepted as providing the greatest assurance of even and
continuous ventilation air flow. Unfortunately, this approach is also the most
expensive, often comparable to the cost of insulating. A typical attic retrofit includes
some combination of gable vents, roof louver vents, soffit vents, and turbine vents.

The following descriptions of passive venting strategies are based more on anecdotal
evidence and a consensus of practitioners than on actual measurements (see Forgues,

1985 for a more detailed discussion of attic venting strategies):

" Gable vents, usually consisting of a set of horizontal louvers shaped to discourage
the entrance of precipitation, are installed on vertical surfaces in the attic. They
can provide high flow rates but depend strongly on wind direction. They are
inexpensive and are often the only existing ventilation,

however they do not usually provide good air flow at lower portions of the attic unless combined with
soffit vents. They do not get covered with snow but may allow entry of winddriven
snow in some circumstances if not properly re-designed when installed
(some contractors fasten a thin layer of fiberglass over the opening and fabricate
a drip tray with flashing in order to avoid snow entry). Contractors report
commonly finding plastic over gable vents installed by homeowners to solve this
problem. The large air flows through gable vents have also been reported to
create suction at roof louvers and thus draw snow into the attic. Roof louvers, sometimes called mushroom vents, are mounted on sloping portions
of roofs near the peak. Used alone, they can leave dead zones and may create
localized moisture problems as moister air escapes through them.

They are more effective if used high near the ridge and in combination with low venting such as
soffit vents. Because roof louvers usually provide only 40 to 80 square inches
of net free vent area each, it is often impractical to install enough of them to
meet code. In regions with high snow loads, roof louvers may become
completely covered in snow rendering them useless during the coldest weather.
m Soffit vents are installed in soffits, of course. They may be continuous or may
consist of a series of individual vents, particularly common in retrofits. They
depend less on wind direction than most other types of venting and can provide
nearly continuous ventilation air directly up along the roof deck when used in
combination with higher venting, such as ridge or roof louvers, which promotes
stack effect (i.e. buoyancy-induced) flows within the attic."

Ed the Roofer 01-18-2008 10:45 PM

By the way SandyMan,

That was an awesome display of all of the work you did. It feels good to actually put a face and image to the person I have been having ongoing discussions with over such an extended period of time.

Thanks for posting them up. Great Job!!!


sandyman720 01-19-2008 07:10 AM

THanks Ed. Not too bad for an accountant huh?!

Ed the Roofer 01-19-2008 01:41 PM

Not too bad at all.

I had you pegged for being much older than you are from your pictures doing the roofing work. Did you get that felt paper nailed down flatter before installing the shingles though?


the roofing god 01-19-2008 02:34 PM

install smartvent above the freezeline for intake venting,and cover the gable louvres

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