Ridgevent without soffit vent - question


#1

Hello again,

Thanks for advice on the small cottage we just re-roofed!

One more question - We ended up putting Ridgevent on the peak of the cottage and patched up the can vents. Regarding the soffit ventilation - We have vents in every third Soffit, but we believe the Soffit vent is not working properly as either the insulation in covering the open space or the cottage was not built correctly. So…we planned on just putting in Gable vents. While purchasing the gable vents at a supply house - I was informed by the employees and fellow roofers, that you do not want to install both gable and ridge vents. You need the air coming in low (Soffit) and exiting high (ridge). By the way, I do not have access to the attic. The cottage has no entry to the attic!

So…wanting to do this right - what are my options?
Is is possible to correct the venting problem from the outside of the house and going in thru the soffits? what if an opening has to be cut???

THANK YOU!


#2

“you do not want to install both gable and ridge vents.”

That is correct. You would get negative air flow.

If you have insulation blocking your soffit vents the optimal way to correct it would be to gain access to the insulated area (most likely while the roof decking is removed.) and install baffles. They make baffles that are designed specifically for the purpose of creating space for air flow. If you don’t have access to the insulated area causing the problem your best best is probably to use gable vents and have a fan in one of them to keep the air moving. Most companys prefer ridge vent in conjunction with functioning soffit vents and anything else is usually considered an inferior solution.


#3

or remove the fascia,and install raftermate thru there,if it`s cathedral and the insulation has no breathing space ,it will ruin the roof/sheathing prematurely


#4

Ridge vent and gable vents work well together.

It is helpful to also have soffit venting if possible.

Here is a link to some basic ventilation scenarios. It is not quite complete but it may help.

Attic Ventilation Basics


#5

yea to an extent,but not as well as w/soffit vents,and when you have both gable and soffit vents,it interferes w/air flow


#6

Thanks for your reponses!

I am still a little confused! Dennis’ link says you can do ridge vent and gable vent, but the others are saying they do not work well together!

I will call local pro to look at it!

Anyone else have any thoughts?

Thks


#7

Physics isn’t my forte but I don’t think those diagrams are correct.


#8

Ok did some googling and found a pretty killer vent link:

roofhelp.com/ventilation_main.htm

Enjoy!


#9

Cor-A-Vent has a new product called IN-Vent that may help: http://coravent.blogspot.com/2007/03/new-product-in-vent.html


#10

Tar Monkey, I’m curious as to what you think is incorrect about the diagrams???
Without talking physics or computational fluid dynamics, can you explain your concerns in laymans terms?

Steve, in some instances, even good ventilation will not prevent ice dams. If ice damming is a problem, I would stay away from the type of vent that is cut into the lower part of the roof. The DCI fascia vent would be a better option. IMO

Bob15201, I think most roofers have just not done the research. And the ridge vent companies have done a great job of selling their story.


#11

Ok, well the first 4 examples assume this:

“. The attic floor is well insulated with minimal air leakage from the living space below.
. There is no breeze.
. The outside air temperature is 85 degrees
. The temperature inside the attic is 140 degrees
. The ridge of the house runs east to west.”

Sadly the real world isn’t like that. The houses I roof exist in a variable environment not a static test facility.

The second example for instance is not correct or at the very least the illustration leads the reader to believe that ridgevent alone is enough to adequately ventilate a house. Even if cold air goes in and hot air goes out you would have to have the world’s largest vent to have both adequate intake and exhaust to vent a bird house let alone one for the average sized human family. Also it fails to state that air blowing across the vent can allow snow and moisture to be sucked in the vent.

While I like all the pretty lines and arrows of the final examples where there is actually a breeze blowing and the high and low pressure doo-dads I can’t verify any of that crap. I do know that according to those diagrams that ALL roof ventialation combinations work which is in fact BS. Ventilation is the number one incorrect spec for all roofing projects for the simple reason that not ALL combinations work.

I can tell you that breeze, no breeze, whatever…When using ridgevent in conjunction with some kind of soffit/eave vent that the hot air rising out the top of the roof will suck in fresh air from the soffit/eave vent. If you also take a few minutes to do some basic arithmetic and apply the 1/300 rule you will have a ventilation system that functions properly.

I mean geez the very last example has soffit, ridge and gable vent installed, lol.

The link I posted actually explains ventialtion pretty well, it’s not a difficult subject. Anyone that takes the time to read it will quickly spot a few of the problems I’ve touched on.


#12

if you have no soffit vents,gable vents work ok,but air circulates from vent to vent,so with gable vents to ridge you do not ventilate the entire area,whereas w/soffit vents and ridge vents you create cross ventilation through the entire attic space(w/gable vents closed)----do this–go to a part of the house w/ windows on each side of the room,open 2 windows 3-6 ft. apart,see what kind of breeze developes,now shut the 2nd window leaving one open on that side of the room,go to the opposite wall and open a 2nd window,you will find much beter air circulation because of cross ventilation—its not a ridge vent mfgr.s sales pitch-its a proven fact in many applications! if you doubt it do the test in your own home and see for yourself :wink:


#13

Dennis - In response to your concerns about ice dams and the IN-Vent, Cor-A-Vent recommends installing IN-Vent 36" up from the drip edge to avoid that very issue.
I’m not sure if by DCI fascia vent you mean their SmartVent product, but if so, you’ll notice that DCI shows the installation of that product at the drip edge, which would heighten the chance for ice dams.
Here’s a link to see some of the differences between IN-Vent and SmartVent (and I swear this is the last time I’ll link to this site): http://coravent.blogspot.com/2007/04/in-vent-vs-smartvent-cage-match.html


#14

Tar monkey, Thanks for the reply. That’s just the kind of critique I was looking for. I will use it to add clarification to the web page.

The examples all have the same basic variables for illustration purposes. Those variables stay the same and only the venting and wind direction changes. If I were to add in all the variables in design and weather I would have to write a book. Remember the title was “Ventilation Basics” :slight_smile:

The purpose of the illustrations is just to show how the heat and air circulate through various venting configurations. The ridgevent illustration is not meant to be taken that it is enough to vent an attic. It just shows that hot air will escape the attic and cooler air will move in to replace it.

“not ALL combinations work"
I see it as " not all combinations work perfectly”.
Take illustration 6, it shows ridge and soffit vents and wind blowing parallel to the ridge. In that situation, the venting is inadequate. If you add gable vents as in illustration 7, the venting is greatly improved. I think it is better to have ventilation that works most of the time than ventilation that only works under certain parameters.

TRG, Ridge vent and gable vents will ventilate the attic. The addition of soffit vents will enhance the venting, but having all three, in most cases, will not detract from the ventilation.

I will work on adding more information and clarifications to the site.

Steve, sorry, I didn’t see that spec. That would be better.
But I was thinking of the DCI fascia vent that installs behind the gutter and vents near the soffit. I’m not sure right now of the exact name. Much better for an ice dam problem area.
Maybe coravent could design a better one??? :smiley:


#15

Ok, well, we will just have to agree to disagree then.


#16

i agree that it will work DENNIS,just not as effectively as it does with soffit vents instead