Thread: Impact of combining topside and ridge vents?

Does anyone have experience or information about the impact (positive or negative) of having both topside and ridge vents?

I just inspected an attic with both, and it was extremely hot. I'm concerned that the ridge vent is pulling air from the topside vents and somewhat negating the soffit vents. I'd like some documentation to substantiate or disprove my theory.

Any help would be appreciated

Thanks

John

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Originally Posted by John Bernard

Does anyone have experience or information about the impact (positive or negative) of having both topside and ridge vents?

What are topside vents? Are you referring to off-ridge vents? Gable vents?

He probably means regular roof vents, the square aluminum jobs everybody puts in.

Yes, the regular roof vents

Originally Posted by John Bernard

Yes, the regular roof vents

I call them static or can vents....

You are defeating the ridge vents if you have both. The cooler air will enter the can vents and then the hot air exits a few feet later through the ridge vents. It is an either or and not both!

You want the cooler air to enter at the lowest level (soffits) and then allow it to start the chimney effect to push the hot air out the ridge vents. This way you are moving most of the air in the attic area.

Scott,

Thanks for the input. I thought that would be the situation. Do you have any references that I can share with my client? Unfortunately the roofing contractor they have thought it best to ADD the ridge vent.

What is your opinion on adding thermostatically controlled fans to the static vents to force air out? Do you think that would compliment the ridge vent, or is this a waste of time?

One more question while we're on the topic. Is the configuration of the static vents important - i.e. all on the same side of the roof, as opposed to on oposite sides?

It's clear to me that proper attic venting is much more complicated that it appears on the surface.

Thanks again!

John

I don't know about Scott's answer. It may be that stack effect would continue to draw from the rest of the attic. I have seen multiple types of vents with no problems. Then again, it's early in the morning and I may be a bit dopey...

I always discourage the use of power attic ventilators. Purely a waste of energy and can cause other problems in certain circumstances. Passive balanced venting is best.

I don't have documentation or reference to support my logic, but in Scott's explanation (both can and ridge vents together defeat full ventilation) surely depends upon the placement of the roof/can vent in correlation to the ridge vent. If the can/roof vent is high enough and in close proximety to the ridge, then they would act in concert, not in opposition by both together drawing cooler air from the soffits. The hot air in the attic at the ridge would not be significantly different, a few feet below the ridge, if that's where the can vents were installed. I would make sure that there was adequate soffit venting with properly installed baffles. It also makes a difference as to which side of the roof has greater exposure to the sun. Placement of soffit and can vents on the shady side and/or a side with greater exposure to wind and external air currents is also important for optimum passive venting.

Originally Posted by Jim Luttrall

I always discourage the use of power attic ventilators. Purely a waste of energy and can cause other problems in certain circumstances. Passive balanced venting is best.

While acknowledging that there is at least one member on this board who apparently absolutely despises "other problems" and "other issues" and recognizing that said person appears to not be able to comprehend the mixing of
"other problems" and "other issues" with the main topic at hand, even though the rest of us realize the benefit of at least mentioning that there are "other problems" and "other issues" ...

Yes, one of the main "other problems" I believe Jim is referring to when using power ventilation in the attic is creating a negative pressure within the attic, and the negative pressure within the attic sucks conditioned air from within the living space, and that conditioned air is replaced with unconditioned air from outdoors ... and that air must now be conditioned. Thus there is an energy use above and beyond that of just the power ventilator.

Additionally, one of the other problems could be the outdoor air which is being drawn into the living space - that air could contain allergens to which the occupants of the house are allergic. Typically, outside air is better than inside air, but when allergens are considered, and with the filters available today, some people have an easier time breathing the indoor air than the outdoor air.

There are, I am sure, even other problems which could be, and should be, considered (by most people, there is at least one here who seems to despise considering those other problems ... right Ken R.?)

I installed ridge venting on my house last year. I don't remember if it was in the product literature or not but I did call the manufacturer and specifically asked about the existing gable vents and was told to cover or remove them because they will interfere with the air currents that the ridge vents create. For efficient venting you want equal or better low roof or soffit vent area to ridge vent area. If the high/ low vent area is not equal it is only ok to have excess on the low side. The tech support guy was clear on this point. I have roughly twice the soffit vent area as the ridge and it works very well, all my gable vents are covered on the inside of the attic.

Originally Posted by John Bernard

Do you have any references that I can share with my client? Unfortunately the roofing contractor they have thought it best to ADD the ridge vent.John

Here is a reference that you can share with your client.
A Crash Course in Roof Venting — Building Science Information?
In short, you want to have somewhere between 50% and 75% of your venting at the eaves in order to prevent pulling the conditioned air out of the house.

Originally Posted by John Bernard

Scott,

Thanks for the input. I thought that would be the situation. Do you have any references that I can share with my client? Unfortunately the roofing contractor they have thought it best to ADD the ridge vent.

What is your opinion on adding thermostatically controlled fans to the static vents to force air out? Do you think that would compliment the ridge vent, or is this a waste of time?

One more question while we're on the topic. Is the configuration of the static vents important - i.e. all on the same side of the roof, as opposed to on oposite sides?

It's clear to me that proper attic venting is much more complicated that it appears on the surface.

Thanks again!

John

Sorry for the late reply, busy weekend!

I do not recommend power vents... They can and do cause more problems than they solve, IMVHO..

University of Illinois did a great study on roof ventilation that covers most of these questions about 3-4 years ago. Google u of i ventilation.

Here is some good info
http://www.airvent.com/pdf/literature/PAVbooklet.pdf