Roof vents

[HarmsWay]

If possible I'd look at the local building code and/or talk to your building inspector. For my location, I believe they were quite specific and I'm pretty certain soffit venting was required (for condensation as docrowan mentioned). Good airflow is very important.

Bob

[docrowan]

JimD made a great point I hadn't considered. The soffit vents probably have a great deal more area than the ridge and gable vents put together. Therefore you'll still be pulling air along the underside of your roof sheathing to reduce condensation and frost in the cool months.

Well, I guess if you ask 3 forum members a question, you'll get 4 opinions if I'm one of the three.

[HarmsWay]

This is from IKO, a company that manufactures roofing products (shingles, vents, etc.)

"When determining the need for additional vents, a ratio of 1 sq. ft. of net
free area for every 300 sq. ft. of insulated ceiling area, divided in equal
proportions between the soffits and the peak of the roof, is required by most
building codes. 1 sq. ft. of net free area for every 150 sq. ft. of insulated
ceiling area is required for low sloped roofs. The net free area is usually
stamped right on the vent by the manufacturer."

They also state several times "Never mix different type of vents on the same roof.

I would think that in Ohio it would be possible to have too much ventilation. Wouldn't that increase heating costs in the winter?

Bob

[Kristofor]

I would think that in Ohio it would be possible to have too much ventilation. Wouldn't that increase heating costs in the winter?

Bob

Yes it would have an impact on heating but....

If your "cold" attic area is actually warm you will tend to melt the snow that's on the roof, which will then run down to the overhangs (which are cold) and refreeze forming an icedam. This can then build up more ice or worse water which will try its best to ruin your roof.

So, add more insulation to help with heating costs but keep the roof cold at the same time.

[HarmsWay]

Agreed, but the discussion was more for leaving gable venting in as well as ridge venting. That would do a good job of keeping the peak cooler but not so much the low parts, which is where the icing happens. I'm no roofing expert though.

Bob

[Salty]

Well, OK, I think I'll put this to rest now.
I am going to leave them in.
My calcualtions are thus:
My net free area is around 1200 sq ft.
That requires a total of about 4 sq feet of vent.
Split that between the ridge and soffit(assuming the gables are not there.
I have about 1.9 sq ft of soffit vent so that is about half.
With the 40 ft of ridge vent there will be about 4.4 sq feet at the ridge.
That's 2 times the soffit.
So, it is possible the ridge could draw from the gable, but it wouldn't detract much from the soffit.
Besides, there is the advantage of natural flow of warm air rising, I doubt it will be a problem.