Attic ventilation for gambrel roof


#1

We have a gambrel roof (front only) with 5 dormers in front with significant ice damming last winter that caused over $32K in damage. The ice damming occurred in the front only. We had an energy audit and air sealed the attic, plus increased the insulation significantly. They sealed off whatever soffit vents we had. We need a new roof (and will get winterguard, which we didn’t have) and need to figure out what is the best venting solution.

The ventilation now consists of two gable vents and a disabled attic fan. The energy guy recommends adding a ridge vent to go with existing gable vents. I don’t think this will ventilate the attic, but he is adamant that it will, saying that “thermal movementâ€Â


#2

Skip the Wintergaurd and insist on the real thing, Grace Ice & Water Shield.

It doesn’t sound like your ice damming problems can be fixed short of a cold roof.

Paying 2x as much for Grace as opposed to the other so called Ice & Water Shields is well worth it in your situation.
Grace actually works when needed, Winterguard doesn’t.

Insist on Grace Ice & Water Shield, and to go the extra mile insist that the portions of the roof that experience ice damming get hand nailed with hot dipped galvanized nails at minimum.

The Grace will keep the water out for a very long time, the weak link is the fasteners.


#3

thanks - I’ll look into that. What about the ventilation issue? Should I go ridge vent/gable vent or one of the other ideas?


#4

Before you worry about your exhaust vents you need to have intake vents.

With a gambral roof and several dormers soffit/intake ventilation can be difficult to achieve.

Without intake vents ridge vents won’t work.

There are ways to make this work dependent upon the structure.


#5

When people have had serious ice dam problems it isnt a bad idea to run a heat cable in the gutter and up along the walls. No need for the zigzag. Just somewhere for the water to go during the melting of the icedam.


#6

The perfect place to use vented drip edge…at the brake if there is no gutter.

No reason to use the “new modern stuff” here. Vented drip looks better


#7

Thanks Axiom - the energy guy told me that the gable vents would function as intake. It didn’t sound right to me, which is why I got the other 3 opinions.

Gus Jones: Thanks for the idea. The vented drip edge would be a similar issue to the edge vent - it would only run between the dormers, right? One thing I’m concerned about is that the total intake will not equal the exhaust since the dormers take up about half the front. So it would be a total intake that is 75% of the total exhaust. Of course, this would be better than what I have right now. The smart vent, riding higher up on the roof, would give an equal intake/exhaust.

RooferR: I live in VA where we rarely get big snows. This year there was 4’ on my roof when the trouble started. Do you think we could do a heat cable that we put up in the gutter only when they are predicting a big one? (and possibly up the walls, as you say, which I take to mean the parts between the dormers?)Thanks


#8

I would do smart vent and ridge only if the attic has the proper insulation and like axiom said watch what you buy, you will get what you pay for.

The roof with the smart vent will do wonders. i do not use edge vent. you have to pull the gutters down and if they dont it looks horrible. If there is enough ridge to support the home then use it.

a 1200 square foot attic area would need 16 feet of ridge vent using the 300 rule and thats the only one you can use with ridge vent. With that i would like to say having baffles installed if the home has a vaulted ceiling is a must, the air must travel thru there or it will not work.


#9

Thanks gtp1003. I like the smart vent too, but am a little worried that having it up higher on the front (1’ past where the dormer meets the roof) might be a problem with the ice dams. hh


#10

How About some pics. And grace is the best ice shield for sure. But gable vents and ridge vent only vent the top three feet of the roof. Think about where the air comes in that gable and where it will exit at the ridge ( Top three feet). Anyway the best way to solve a ventilation dilema is to see pics


#11

I’m guessing this house looks like a barn with a bunch of dormers, with the dormer valleys draining at the pitch transition.

If this is the case I don’t think I would use smartvent between the dormers.
Vented drip would be much better in this scenario like Twill said.

Each of these dormers is blocking airflow also so how much intake you can actually achieve is limited.
This could require a creative solution.

Just a guess. :smiley:


#12

Bigbrody22001: Here is a pic of the front. The back is just a normal roof, and coincidentally didn’t have any ice dams.

Axiom: One of the roofers suggested using smart vent done about 1’ from where dormer meets the roof (slot would be about 4’ from roof edge where there is no dormer). Does that sound reasonable?

%between%http://i1111.photobucket.com/albums/h471/hel2662/th_IMG_1695.jpg


#13

Theoretically the smart vent combined with exhaust vents will keep the ice dams from forming in the first place.
Smartvent and edge vent are both relatively new products, I wouldn’t be comfortable putting smartvents too close to those valleys.
Perhaps your dormers are framed in such a way that the dormer ridgevents could act as intake vents?
It doesn’t look like there is much room to get smartvents or a decent amount of drip edge vent near the pitch transition.

Perhaps Tinner or Shangle Nailer are in your service area.
If they aren’t they may know someone who is really good that is in your area.

Can you post a picture of the entire front of the house showing all the dormers?
A cold roof on the upper lower slope portion is looking like the most effective solution at this point.


#14

Thanks Axiom. The roofer was planning on putting the smart vent about 1’ up from where the dormer hits the main roof, about 4’ from the edge. Do you think that’s too close?

I don’t know how the dormers are framed. The house is 32 years old, if that helps (?) I’m up in No. VA

Here’s the best I can do with a front view.

%between%http://i1111.photobucket.com/albums/h471/hel2662/th_IMG_1697.jpg


#15

You can have the heat cables up all the time and control them with a switch. For roughly $150-$200 you can have an electrician run a plug outside with a switch in the basement for it.


#16

i do not care for the now that i seen the house on smart vent being that close to a valley. Now heat tape all it does is move the issue farther up the roof in what i have seen way to many times.


#17

Hi everyone,
Sorry I haven’t posted for so long. I kept trying, but there was something wrong with my server and I couldn’t access the board for the past week. I hope you can still take a minute to look at my problem.

It seems like, based on what everyone has said, that there is no perfect solution for my problem. I’ve talked to air vent and dci products, and both think their solution will work. Here in northern VA we don’t get many ice dam-worthy snows, but I lost so much $$ this time that I don’t want to go through that again. I need to make a decision this week so I can hire someone to do this roof before it gets too cold. I have significantly insulated the attic and airsealed the ducts up there, so that will help a lot. There is a disabled attic fan up there as well.

The two options proposed by my roofer(both will close off gable vents, add a ridge vent, and will have edge ventilation in back):

1)smart vent 1’ up from dormer peaks all the way across(4’ from transition). note: gtp1003 really dislikes option 1

2)“edge vent” at transition between each dormer, which is lower down but won’t go all the way across, of course

I am so stressed by this decision because of all the problems from last winter, that I really feel like I’m paralyzed from making a decision. I would be grateful for any help in making the choice. Thank you. hh


#18

Cant you open up the soffits again?


#19

This is the Gambral roof she was asking about last week.

It sounds like your roofer has a pretty good handle on the situation.
My concern was the smartvent being too close to 2 valleys, and the possibility of ice backing up into the smartvent.
My opinion is based on my experience in my climate, we probably get significantly more snow and ice in Northern Michigan than you get in Virginia.

Your roofer is from your climate so chances are he is a better judge of what unconventional procedures will perform well in your area than I am.

It sounds like you are in good hands.

I still think that a cold roof on the upper portion is the ideal solution.


#20

kage: Unfortunately I can’t open the soffit vents again because of the way they did the insulation.

Axiom: That’s reassuring, though I think no one down here has much experience with 4’ of snow. :wink:

Isn’t this plan giving me a cold roof? I thought that was what we were trying for - maybe I don’t understand it very well. hh