Does a Roof Need a Ridge Vent? - Fine Homebuilding

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Breaktime Spotlight

Breaktime Spotlight


Does a Roof Need a Ridge Vent?

comments (6) September 3rd, 2013 in Blogs
ScottG Scott Gibson, contributing writer

There are many opinions about the benefits of and problems with roof venting, but it all comes down to proven rules of building science. Read the discussion below to see what builders and homeowners are typically dealing with, but then read A Crash Course in Roof Venting to find some proven roof-venting solutions.Click To Enlarge

There are many opinions about the benefits of and problems with roof venting, but it all comes down to proven rules of building science. Read the discussion below to see what builders and homeowners are typically dealing with, but then read A Crash Course in Roof Venting to find some proven roof-venting solutions.


Pizza's sister lives in a house in Bucks County, Pennsylvania, that was built in the mid-1980s. Like many others of the era, the house has a gable vent at each end of the attic, along with soffit vents at the eaves. Working in tandem the vents have apparently done their job.

Now the house needs a new roof, and the contractor is recommending that Pizza's sister install a ridge vent.

"I have learned here (building science articles here on this web site by Joe Lstiburek) that in her case ridge vents are unnecessary and actually detrimental to cooling the attic space/roof when you already have gable and soffit vents, something to do with gable vents overpowering the vented soffits," Pizza writes in a post at Fine Homebuilding's Breaktime forum.

"Should I tell my sister that she can tell the contractor to NOT install the ridge vents?"

That question is the topic of this Breaktime Spotlight.

Block the gable vents, or maybe not

DanH is among those who think the best strategy is to block the gable vents and go along with the contractor's suggestion to install the ridge vent.

That, he says, is the "proper thing to do."

"Not necessarily," counters Seeyou. "If there is not a proper soffit or other intake, then the ridge vent won't function," Seeyou writes. "I've seen lots of gable attics where one gable vent was the inlet and the other, the outlet. More info is necessary."

Despite Pizza's assurances that his sister's house has vented soffits, xxPaulCPxx contends they may not be large enough, or numerous enough.

Some builders doubt gable vents are effective

Hammer1 has given up on gable vents entirely.

"The reason we changed from using gable vents is that they don't work," Hammer writes. "Hot air in the attic forms pressure and won't allow outside air in. If they work at all, it's usually just in the area close to the gable vents, not the entire attic. The combination of a ridge vent along with continuous soffit vents gives you a flow through of air similar to the way a chimney works. Even without soffit vents, a ridge vent is much more effective than gable vents."

PaulCP thinks Hammer is right. "The problem with gables is they short circuit the air flow," PaulCP writes. "The whole point to a ridge vent is that it takes air from all along the bottom of the roof line and exits it out the top, kind of like a toilet. You WANT all the sides to be washed. That doesn't happen when most of the flow is from two specific points."

Hammer says, however, that blocking gable vents isn't necessary. "The whole idea is to keep the attic as close to the outside temperature as possible," Hammer says, "getting the accumulation of hot air out."

Not according to the manufacturers of ridge vents, DanH adds.

"I'll admit I haven't looked recently," DanH says, "but in the past the manufacturers of ridge vents recommended blocking off gable vents when intalling ridge vents (assuming that adequate soffit venting is in place). The reason is to keep the gable vents from drawing in air and reduce the draw on the soffits."

"Moving the maximum amount of air is what it's all about," Hammer replies. "So what if air comes in through the gable vents, it will just add to the flow, hot air rises."

PaulCP also thinks the benefits of closing off gable vents is marginal.

"Too much focus is placed on closing gable vents with ridge vent," PaulCP writes. "In laboratory testing, it might increase the functionality of the ridge vent somewhat. In real life, it's not worth the trouble and more venting is usually better than less."

What happens when snow blocks the ridge vents?

In snow country, ridge vents may be blocked by drifting snow during the winter and therefore unable to work correctly. At least that's the concern voiced by Kdesign.

"The reason I ask is that I am in Minnesota where we get considerable snow, and yet ridge vents seem to be the preferred discharge vent," Kdesign writes. "I have never heard anyone mention a concern over the fact that ridge vents are probably blocked at least half the time over the course of a winter.

"I sometimes wonder if many people believe that ventilation in the roof system is to keep it cool in the summertime," Kdesign adds, "and don't realize that the primary purpose is to control cold weather issues. With that belief, snow plugging the ridge vent would seem irrelevant."

DanH says ridge vents remain effective in winter because winds generally clear the ridge within a few days of even a heavy snow, and because warm air working its way up through the attic will melt snow covering the vent.

"Certainly there are situations where conditions can be so severe that neither of these occur in a timely fashion," DanH adds, "but they are rare in Tropical Southern Minnesota."

DickRussell admits that under certain conditions, a layer of ice-encrusted snow can cover and block ridge vents. But overall, he thinks they remain functional most of the time.

"Why do I think this?" he writes. "In a cottage we used through a few winters, I used to see a lot of wetness from moisture in the house condensing on the underside of the roof deck. There were gable vents but no ridge vent. After I re-roofed the place, with a ridge vent installed, that surface stayed dry essentially all the time."

Kankan writes that his well insulated roof has no problem with ice dams, as long as the ridge vent is visible. "But when it gets buried," Kankan adds, "bam, dams."

"I have seen with my eyes my ridge vent get completely buried in snow and saw results of lack of ventilation instantly," Kankan says.

Maybe, DanH ventures, there is no single answer to this puzzle.

"I think the thing is we all have different experiences, based on where we live and the construction of our homes," Dan writes.

 


For detailed information that could help you deal with your own roof-venting issues, read:

A Crash Course in Roof Venting
Understand when to vent your roof, when not to, and how to execute each approach successfully

Crash Course in Roof Venting

 

 


posted in: Blogs, roofs

Comments (6)

Carl_H Carl_H writes: I like your article because it is so interesting to read. Ridge and softfit venting is great if you have a simple gable roof. But it is always depend in what we need. I read this article http://www.approvedremodeling.com/blogs/what-correct-roof-venting-means they said that "A good ventilation system is one that has an equal number of high vents or exhausts and low vents or ingresses and that would allow smooth airflow".
Posted: 8:39 pm on August 21st

user-2738415 user-2738415 writes: Soffit and ridge venting is great if you have a simple gable roof. How many homes these days are built with a simple gable roof? What happens to this venting strategy at the corners of hip roofs, when dormers and skylights are added, when other parts of the roof butt into this vented roof?


Posted: 10:57 am on September 12th

HandyinAtlanta HandyinAtlanta writes: Perry525 thanks for your comment. That explains why my house was freezing cold last winter. I had a new roof installed and they added ridge venting, which my house didn't have. My house was built in 1940 and has no insulation in the walls. I did add insulation in the attic.

I have been living in my house for 20 years and it has never been that cold. I had a family member visiting and she noticed it too. I had a new furnace installed 2 years ago and all was fine, until the ridge vents. I asked the roofer about that and he said having the ridge vents shouldn't make any difference, maybe I needed more insulation in the attic. I may consider spray foaming them closed.
Posted: 9:32 pm on September 10th

rnault rnault writes: Years ago, I attended a seminar on continous soffit and continuous ridge venting. The model used a fine white powder to see how air flowed from the soffits to the ridge. Every rafter bay had a continous flow of powder from the roof eave to the ridge. The model with soffit vents and gable vents only had continous air flow from the sides where the gable vents were located. Not accounting for swirling winds and other abnormal conditions, the soffit/ridge venting seemed to be the way to go.
Posted: 1:36 pm on September 9th

JosephHunt JosephHunt writes: I live in a Victorian style 2-story home. Originally, there was not a ridge vent, only gable vents on either end with 1 1/2 inch holes in the blocking between the trusses. The second floor of the house was always hot and sticky regardless of how low the air conditioning was turned down to. After considering zoning my upstairs with a separate air conditioning unit, I decided that I would go to a ridge vent first because I had a ranch style home in the same area that was built with a ridge vent and was always comfortable. After installing the new vent on the Victorian, the results were felt immediately. The upstairs heat was broken, allowing the upstairs temperature to drop a good 10-15 degrees without touching the thermostat. I did not block off the gable vents, reasoning that depending on wind conditions, they would still serve a purpose. Sometimes the simplest solutions are not only the cheapest, but the most comfortable.
Posted: 9:59 am on September 9th

Perry525 Perry525 writes: When the wind blows over a roof, it acts like an aircraft wing, providing uplift, this creates a low pressure area to the lee of the building, which sucks the air from inside the roof.(and your home)
People may ague that the low pressure area sucks out warm air from the roof in summer, good - But, not so good, it also sucks out warm air in the winter, pushing up your heating bills.
If you are interested in keeping your heating bills down in winter, and your cooling bills down in summer, you should make sure that there are no holes in your ceilings for your expensive heating/cooling to be sucked through.

The only way to find out if, you have heat leaking into your roof during the winter/or cool air escaping during the summer is to buy and use a Weather Station that has two sensors, put one in the roof and the other outside, if they both agree you have one well made home, if the sensor in the roof shows different temperatures and humidity, your ceilings are not good enough.
You can upload the data 24/7 onto your computer and see, from the temperature and humidity readings if indeed your ceilings are airtight and your insulation is adequate.
Posted: 2:14 pm on September 6th

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