Roof vents

[Salty]

Hey all.
I'm fairly comfortable with my opinion on this but I thought I'd throw it out there and get some other opinions.
Here's the setup. The house is a 4-12 pitch, straight ranch with gable ends. I recently had the attic insulated and they installed baffles between every rafter, and it is truss construction. Also, I recently installed new vented vinyl soffit so there is sufficient airflow from the soffit to the attic.
Now, I will be having a new roof installed soon and it will be a 2 layer tear-off. So, I'm thinking this is a good time to install ridge vents. However, there are already gable vents installed, one on each end adout 12" wide and 16" high.
One of the gentlemen who gave me an estimate said that the gable vents would have to be blocked off if ridge vents are installed.
This seems wrong to me. It seems to me that they would just aid in the venting of the hot air on the ends.
What you guys say??

Thanks.

Salty

[JSUPreston]

Don't know if this will count, since the contractor 1/2 a$$#d the job, but our addition only has the ridge vent. No gable vent at all. I have to admit that your opinion makes sense to me as well.

[cbrown]

We just had the roof redone and a ridge vent added. The gable vents remain open. Our cape has no eaves, so no soffit vents, if that makes a difference.

Chris

[Sid]

I'm having a roof replaced and considering venting methods. Contractor explained to me that since end gable vents are lower than ridge vents, the end gable vents can become the inlets, short circuiting the inflow that should come from the soffit vents.

Sid

[crokett]

What Sid said. I asked my A/C guy this question a while back. That was his answer.

[axa]

There is apparently is this virtual vacuum formed from the soffits to the ridge vent but the way I figured it is the hotter air will flow up no matter what, be it from the gable or soffit vents.

I have both as well as 4 square vents a few feet from the top as well.

Just today, as I installed the ridge vent and as I opened the ridge, a mass of hot air just oozed out.

From what Ive learned from experiance is that a ridge vent helps in any situation.

[Salty]

Thanks for all the replies.
I did some web searching and found both opinions. I guess it can be argued both ways. Seems to be a re-occurring theme that the gable vents "short-circuit' the air that should come from the soffit.
I have plenty of open soffit vent so my counter to the above would be that if there is enough air able to enter the soffit, there should be the same or 'more' places for it to exit at the top.
My other concern has to do with the snow. This last year I had 10-12 inches of snow that persisted on the roof for nearly a week. While this seems to me to be an indicator that the ceiling is well insulated, it also seems to me that a ridge vent would be either closed up or severely hindered by such a snow load.
I also have yet to see any real test data on this phenomenon.

[Red88chevy]

Interesting question Salty. With the cost of electricity now, I have been doing experiements on my attic temperature the last couple of summers. Everything I read says ridge vents will make a substantial difference, but they also say all other roof vents (outflow) need to be sealed. You're trying to get a balance of inflow (soffit vents) with outflow (ridge vents). Before you have the ridge vents added, take the temperature in the attic for a few days and compare it with the high temp for the day. An unvented attic can be 30 or more degrees higher than the outside temperature. I use an electronic min/max thermometer that I got as a gift a few years ago, don't think they are very expensive, that way you can leave it up there and not have to worry about being up there while it is hot. Then, when you get the ridge vents installed, measure the temperature in the attic again for several days, and you can see how much improvement there was. After that, temporarily block up the gable vents and measure it again for a few days. This way you will find out forsure if the gable vents help or hurt. If they help, leave them open, if they hurt, then seal them up. You'll have to compare both of these readings to the high for the day. My spelling may be off, but I know all about measuring air temperature, as I'm a meteorologist.

[docrowan]

IMHO, the flow of air should run along the underside of the roof to reduce condensation and frost. I can buy into the "short circuit" idea. It may not make a difference in air temperature, but I'd be afraid of eventually having problems with my roof sheathing down low mildewing or even rotting.

[Pappy]

I am getting ready to put a metal roof on with a continuous ridge vent. I was considering gable vents in the future with one of them being powered. Like Salty said, opinions vary, even among the pros.

Another upgrade I was considering is using Hardi vented soffit all the way around the house. Now I am wondering if it would be better to use solid panels under the gables.

[Salty]

I am getting ready to put a metal roof on with a continuous ridge vent. I was considering gable vents in the future with one of them being powered. Like Salty said, opinions vary, even among the pros.

Another upgrade I was considering is using Hardi vented soffit all the way around the house. Now I am wondering if it would be better to use solid panels under the gables.

Pappy, not sure what you mean by 'solid panels under the gables'!
Are you referring to the soffit up the rake of the gable? I wouldn't think that area would be open to the attic as there is usually a rafter the whole way along the rake.

I came across something that was mentioned that makes me rethink this situation. Someone said a contractor told him to close off the gable vents to prevent snow from blowing into the attic.
OK, maybe there could be a situation where the ridge vent worked so well on a mildly windy day and created a negative pressure condition in the attic. This could cause air to be sucked in through the gable vent and introduce snow through there as well. Admittedly the same condition could exist at the soffit, but there would be much less chance the snow would make it to the attic going through the soffit vent holes and through the narrow opening between the styrofoam baffle and the roof deck.

Also, the contractor that I am seriously considering do the re-roof would be using ELK 30 year laminate shingles. He is the one who agreed with me that the gable vents need not be blocked off. However, the installation sheet for the ridge vent that is used with this brand of shingles clearly states that other roof vents, except soffit vents, should be blocked or removed.

Or maybe I’m just thinking about this too much.

[Hellrazor]

Anyone I ever worked with would not put 3 kinds of vents in an attic area. Either you have soffit and ridge/can/turbines OR you have soffit and gable vents. I guess gable and ridge/can/turbines would work as an alternate setup.

[JimD]

More ventillation does not result in higher temperature or more condensation. There may be some airflow between the gable vent and the ridge vent but that will still result in lower attic temperature. The reduced airflow through the soffit vent - if this even happens - will be offset of the cooling effect of the gable to ridge flow. My soffit vents have about twice the area as my ridge vents. I doubt that there would be any gable to ridge airflow in this kind of situation - would still go soffit to both ridge and gable. I have a hip roof so I cannot have gables so I had the builder put in a powered vent. It could pull air through the ridge vent but I don't think it does. It certainly reduces temperatures when it runs.

Jim

[jking]

If you have a ridge vent, you definately do not want any kind of powered vent installed. The tendency is for the powered vent to pull air from the ridge vent instead of the soffit vents

If the gable vent isn't powered, I don't know if it will cause any problems. It may simply make the ridge vent less effective. I do know you have to be careful mixing vent types or you can have problems pulling air from the wrong place.

[Salty]

This is getting more confusing as time goes by.
I took a walk around the neighborhood this evening and did some observing.
While I cannot tell if a new roof with ridge vents had the gable vent blocked, I can tell you this:
There are 3 houses near me that got a new roof AND new siding. In every case, there are gable vents present. AND, there are ridge vents present. Seems to me that putting the gable vents back in would be a waste of money. It would involve buying the vent fixtures that match the vinyl siding and those aren't cheap.
But I will admit that there may be some conractors who would put them in if it meant a few extra bucks on the job. I guess most homeowners would not be as investigative as I am.