Hi. My sister is having her entire original roof replaced (house built in mid 80s) and the contractor is putting a ridge vent on where none existed before. She has gable vents at each end of the roof and vented eave soffits.
I have learned here (building science articles here on this website by Joe Listrbek) 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 the gable vents overpowering the vented soffits.
Should I tell my sister that she can tell the contractor to NOT install the ridge vents?
Thanks to all in advance.
Replies
The proper thing to do is to block the gable vents.
The proper thing to do is to block the gable vents.
Not necessarily. If there is not proper soffit or other intake, then the ridge vent won't function. I've seen lots of gable attics where one gable vent was the inlet and the other, the outlet. More info is necessary.
The OP said it has soffit vents. You don't trust him?
I do trust him... BUT...
Are the soffit vents large/numerous enough?
Depends
Where is the buidling?
How much vent area does she have?
How much area does the code say is necessary?
Ridge vent
The area of the country is : Bucks County PA, 40 miles north of Philadelphia
Don't kknow the answers to those other questions, didn't measure her roof.
The reason we changed from using gable vents is that they don't work. 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 soffet 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. There's no need to block off gable vents when ridge and soffit vents are installed. The whole idea is to keep the attic as close to the outside temperature as possible, getting the accumulation of hot air out.
I'll admit that I haven't looked recently, but in the past the manufacturers of ridge vents recommended blocking off gable vents when installing ridge vents (assuming that adequate soffit venting is in place). The reason is to keep the gable vents from drawing in air and reducing the draw on the soffits.
Moving the maximum amount of air is what it's all about. So what if air comes in through the gable vents, it will just add to the flow, hot air rises. A working ridge vent won't have any snow on the vents. If you get some, the flow isn't working.
The problem with the gables is they short circuit the air flow. The whole point to a ridge vent is that is takes air from all along the bottom of the roofline 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.
The problem with the gables is they short circuit the air flow.
Maybe. But even if there's a short circuit, there's still flow. The focus of venting should be to remove moisture from the attic. Keeping attic heat from encroaching into the living envelope is a function of the insulation/air sealing. Too many try to use attic venting to cool their home.
Too much focus is placed on closing gable vents with ridge vent. In labratory 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.
I'd be more inclined to block a gable vent in a 12/12 roof than in a 4/12, due to the distance of the vent from the bottom of the attic.
What Paul said.
Most gable vents aren't large enough to do anything and the pressure of warm air in the attic prevents air coming in. The flow still comes up from the soffits and if any goes out the gable vents, it will be venting close to the wall where the ridge vents are not. With the exception of high winds blowing directly at a gable vent, air is exiting both through the ridge and gable vents and that's what you want. There is no interruption, just more area for hot air to exit.
snow on vents
You said "A working ridge vent won't have any snow on the vents." Is it not possible that the attic space is insulated well enough or to the put that very little heat gets into the attic or vent shoots in cathedral cases that there is next to no air stack affect (heat rising) to melt the snow? Should that not even be the goal?
+1 on installing the ridge vent and blocking off the gable vents.
But during the winter, won't a ridge vent be blocked by snow much of the time?
But during the winter, won't a ridge vent be blocked by snow much of the time?
Not where I live. There's no one size fits all answer to the ridge vent/gable vent question.
Snow-plugged ridge vent
I asked the question about snow blocking assuming snow country as a condtion. 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. 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 winter.
I sometimes wonder if many people believe that ventilation in the roof system is to keep it cool in the summertime, 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.
I live in Minnesota, and I feel that ridge vents remain effective in the winter (usually) due to two factors:
The wind will generally blow the ridge clear within a few days of a heavy snow. (This happens even on our 4/12 roof at the bottom of a hill.)
If #1 fails, and the attic heats up at all, enough warm air will work through the ridge vent to melt the snow covering it.
Certainly there are situations where conditions can be so severe that neither of these occur in a timely fashion, but they are rare in Tropical Southern Minnesota.
Snow won't necessarily plug ridge vent
If the snow if fairly fluffy, then it is quite porous, and air will flow out the ridge and through the snow, doing some melting in the process. If the snow is so heavy that it's a whisker away from having been rain, then it is less porous. And if the end of the storm brings freezing rain or just rain followed by a cold front, then a layer of ice can form over the snow and shut things down.
Overall, ridge vents tend to stay functioning through the winter, regardless of snow. Why do I think this? 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 end vents, but no ridge vent. After I reroofed the place, with a ridge vent installed, that surface stayed dry essentially all the time.
Good piece on attic venting
Here is a very good and current piece on attic venting, by Dr. Joe himself:
http://www.greenbuildingadvisor.com/blogs/dept/building-science/lstiburek-s-rules-venting-roofs
He just says, "More down low
He just says, "More down low than up high."
Here's another post that says don't worry about it. https://www.finehomebuilding.com/design/qa/close-off-gable-vents.aspx
I don't care either way, just throwing that other article out there.
I personally don't really like gable vents, but that's just preference.
Ridge vent and snow blockage
If you are asking about snow on a ridge vent, means you are worried about proper ventilation to avoid ice dams. So saying roof vent will unclog after a big snow as attic heats and then melts the snow away from vent is craziness. If attack gets hots even for a day or two after a 10-20 inch snow, you gots ice dams because your roof got hot and melted the underside of the snow. Once you have a dam, even a well ventilated roof will gro ice dams as slightly above freezing days will naturally melt snow on roof faster tha ice dam many inches taller than snow.
I got on this comment thread just trying to figure out my own personal roof ice dam problem. I have a well insulated roof as it has snow on it well longer into spring than most of my neighbors, and it seems well ventilated before a really big snow storm, I get no ice dams as long as I seen my ridge vent, but when it gets buried, bam, dams.
Once snow covers ridge vent pretty thoroughly in storm, no air flow to break it open again, as nothing pulling air in from soffit vents, whole system clog and won't unclog until heat from sun and attic combine to melt ridge vent areas, and that can take some time without that air moving much.
I can't believe the lack information on this topic, saw building science . Com guys mention in good article on roof venting in cold, snowy climate that snow is not an air barrier....I'm sorry, why is then that kids suffocate when their snow caves collapse on them? I have seen with my eyes my ridge vent get completely buried in wet snow and saw results of lack of ventilation instantly, more less fire up ice dams, when none exisiting in spite of many small snow acclimating much snow on roof but ridge vent staying clear because storms spread out over time and air flow sufficient to blow out snow.
If some one has some real data or experience about ridge vents and snow I'd love to see it, for now I think the Camdaian that stick with cupola styl, taller vent seem more right, than ridge vents that can get covered.
Im sorry I can't edit the predictive texts mistakes above, IPad editing is not working
If some one has some real data or experience about ridge vents and snow I'd love to see it
I think the thing is we all have different experiences, based on where we live and the construction of our homes.
You say your attic is well insulated, and I believe you. How well is it air sealed, though? Are there any big holes that communicate with the conditioned spaces? Clearance between the chimney and the framing? Attic accessways? Whole house fans? Unsealed recessed lights? Heating ductwork in the attic? I've even seen duct runs with open ends in people's attics.
Poorly sealed is not well-insulated.
True that. However, I was making the distinction to sidestep a discussion of insulation levels. If we can stipulate that there's enough insulation, it focuses attention on air sealing.
I am in your court, ... I think
I posted a question about snow covering ridge vents on this forum sometime ago. If I were to sum up the discussion, I would say "don't worry about, not because I know anything really, but becasue everyone recommends ridge vents". Apologizes to anyone who posted on that thread who may have had a better take on the issue.
I am with you in the observation that snow in my part of the country does NOT melt on ridge vents or can vents. So the question is, how air permable is snow. If it is then ... ok warm air gets out of the attic. I just find it hard to beleive very much air can get through three feet of wet / froozen hard snow. No, I don't have any figures any more than those that say "well it must work somehow".
To address this issue I wondered about building a ridge vent which comes up through the ride and then is covered by its own raise littel roof. I have seen this does on expensive homes in high snow areas and on ski resort buildings. I am sure these vents get covered in snow as well, but maybe air coould run laterally under the "little roof" and out at the gable. Or is it just better to ahve gable vents, of course this would not work on a cathedral ceiling.