Adding Gable End Vents?


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Old 03-02-08, 04:29 PM
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Question Adding Gable End Vents?

In a previous post, I described our Mansard style gambrel Log home. The roof has a ridge vent for the entire length except at the over hangs on either end. During the winter months and especially when snow has accumulated on the roof, the ridge vent doesn't work very well with the accumulated snow covering the vents.
Would I be creating any problems if I added Gable End Vents to each gable end of the attic to help ventilate the soffit vents which lead to the attic and basically have nowhere to vent (during times when snow covers the ridge vent)?
Presently, due to snow depth around the house, I have been unable to access the roof with our ladders. I can see about 12+ inches of accumulated snow on the roof, including over the ridge-vent?
 
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Old 03-02-08, 05:15 PM
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In my opinion, yes, it would create a problem. Gable vents could turn the ridge vent into an intake and pull air down through the ridge of the house, possibly carrying light dry snow or rain down into the roof. Gable vents also short circuit the natural flow of air that rises from bottom (soffit) to top (ridge).

Winter months are usually associated with dry air that contains less humidity. You're also trying to heat your home during these months, so less ventilation during winter months (such as snow covered ridge or louver vents) is not usually a problem. If you are experiencing excess humidity in the home or frost in the attic, then that is a different story. But in general, I would not be concerned about snow on your vents at all.

Some who are from other climates may have a different opinion, and many of them feel that you cannot possibly have too much ventilation in an attic. IMO, that may be true in a climate that is mainly very hot or very humid. But if your climate is cold for half of the year, and also gets hot in the summer, I think most studies show that there needs to be a balance to the amount and types of ventilation that one utilizes on a home.
 
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Old 03-02-08, 05:58 PM
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Adding Gable End Vents?

XSleeper,
Following up on your thoughts, could we install a powered attic vent that could open/close via an electric switch so that we could exhaust any heated air that may accumulate in the attic when the ridge vent is covered with excessive snow?
I have a thermometer in the attic and when snow is accumulated over the ridge vent, the temperature is much warmer than the outside air temperature. The added heat created seems to be the cause of ice dams along the bottom of the top roof portion before the pitch change.
 
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Old 03-02-08, 06:21 PM
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You could, and it would be a better, more controlled solution, but again, anytime the vent would turn on, it will pull air from all available sources, starting with the source of intake air that is most readily available. Power vents rarely ventilate air equally from all parts of an attic- they often pull in a certain percentage of fresh air from the nearest exterior vents. Power vents can also actually create even more heat loss during winter months if they end up drawing and venting air from your living space.

If ice dams are a problem, you probably won't solve the problem by altering the ventilation. Adding insulation/isolating the roof sheathing from the insulation with baffles may not help much either, although you could check into that.

The best way to deal with ice dams is simply to make sure that when ice dams happen, they don't cause leaks, and this is done with roofing membranes prior to shingling. It's almost pointless to go crazy trying to prevent ice dams, because you're fighting mother nature. Certain practices can decrease their frequency or severity, but no matter what you do they will likely continue to happen to some degree.
 
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Old 03-02-08, 06:48 PM
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Adding gable end vents?

We had the top portion roof and the north facing roof/wall re-shingled about 5 years ago. We had them install the ice & water membrane. Since then, all leaks have stopped.
My main concern with the vents was simply to remove trapped attic heat. I do have another concern in the amount of snow that I cannot get removed due to accumulated snow piles around the perimeter of the foundation and house.
Earlier in this winter when the snow wasn't so deep, I was able to position a ladder up on the roof/walls and pull the accumulated snow from the top ranch roof. Now that's impossible with several feet of snow around the house.
Another question in another forum asks about replacing the fiberglass shingle roof with metal in an effort to possibly let the snow slide off the roof or come off from melting? Our top roof is only a 4/12 ranch style pitch.
 
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Old 03-02-08, 07:02 PM
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All I can say is that if you don't have a leak, then IMO, there is no problem. No matter what you do, your attic will likely always be warmer than the exterior temperature. That's natural since heat loss from the house rises, your roofing is a barrier to the elements, and the snow itself is being an effective insulating blanket of sorts.

I wouldn't fixate on this problem. The snow will soon be gone. However, a metal roof would likely be more self-cleaning than a fiberglass-asphalt shingled roof. I can only assume it would lead to an even larger pile of snow around your house, once all the snow slides off and lands on the ground. Unless you have 10' of snow on your roof, I fail to see urgency of the situation. It's likely that everyone in your neighborhood is in the same boat.
 
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Old 03-03-08, 03:58 AM
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Adding Gable end vents?

I guess I just worry about the snow loading up the roof truss system, too much. I will continue to monitor the situation and try to pull off as much as I can get off.
Thanks you for your input.
 
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Old 01-21-09, 07:51 AM
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The Answer Your Were Hoping For

I've been researching this issue for over a year. The bottom line is you should consider looking at a Montreal company named Ventilation Maximum. An independent write-up is here: JonEakes.com > Jon's Fixit Database.

You may also want to research the importance of a perfect vapor/air barrier on the warm side of the insulation. This is EXTREMELY important for cathedral ceilings.

Also, Mr. Tobiasson's paper, http://www.crrel.usace.army.mil/libr.../MP02-5778.pdf is quite good, but doesn't address the fact ridge vents get covered in snow. His research does however point to the importance of adequate and balanced venting and the vapor/air barrier. The paper is a bit of a chore to read and understand, but give it a try. If you have questions, write me.

You might also want to consider Boston Ridge vents. Depending on your taste, they can add or detract from the look of your roof. More info here: Boston Ridge pics - Log Homes on the Internet - Log Home Information since 1995

There are lots of issues to consider when addressing this problem. Due to the problems that ice dams can create, I would not recommend that anyone ignore inadequate venting. I know what I'm talking about. I bought a log home in northern WI and I knew it had a problem with the roof, ice dams, cathedral roof, no air/vapor barrier, 2" bead board insulation, and no ventilation. The previous owner said gutters were never installed because the ice dams tore them off. The extremely poor roof and the lack of gutters has caused thousands of dollars of damage to the logs (decay and water damage). I will be removing the entire roof structure and rebuilding it. After the roof is fixed, I'll have the logs restored. I'm preparing for a VERY large bill and a lot of work. But I can guarantee you that I will not have venting problems or ice dams and my utility bill will be halved. Do not ignore a poorly designed roof; your whole house depends on it.

I can be reached at

first part of email address: nospam
second part: at sign
third part: netcrafting.com
 
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Old 01-21-09, 11:05 AM
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Another Bit Of Interesting Info

Check this document. Very interesting.

http://www.hnd.usace.army.mil/techinfo/ti/809-52.pdf
 
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Old 01-21-09, 12:16 PM
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Hi Rodger,

Not sure why you brought up such an old thread but, hey, those are some nice ventilators and massive ridge vents.

In this case however, the house has an attic and there is no reason not to install gable vents for additional venting if there is adequate soffit venting.

I say that because;

A. I have evidence to support the claim: Roof and Attic Ventilation

B. There is no research or evidence, other than hearsay, to dispute it.

I do like the venting shown as an option for cathedral or vaulted ceilings. For the Boston Vent, a baffle such as that on some ridge vents would help to keep out blowing snow and rain.
 
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Old 01-21-09, 12:55 PM
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Hi dennism,

I stumbled upon the thread and felt that I had important information to share on the same subject and also felt it was important to keep it in the context of thread. It should benefit others who stumble upon it. I was just trying to be helpful.

I didn't comment on the gable vents, but you bring up an interesting point. I have evidence that various vents can be problematic in certain climates.

I live on the open Minnesota prairie. There are no trees, no hills and we get very high winds (50+) and fine blowing snow, aka blizzards. Vents that are not protected with something to prevent it, allow a large amount of snow into the attic. This happened to me twice and caused much interior damage when the snow melted in the spring. I've had to seal those vents to prevent the problem. Forturnately it gets very cold here (did I say that?) and the snow doesn't stay on the roof, therefore ice dams are not an issue. Blocking my vents has not had a downside yet.

My situation in WI is much different than the one in MN and the climate there is much like NH. The info I provided would help anyone facing the same problem that parkpointer has.
 
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Old 01-21-09, 06:28 PM
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I need to add a couple things.

Dennism - I agree with you that it probably wouldn't hurt to add gable vents. If parkpointer doesn't live where high winds could drive snow into the attic, it's probably the most attractive option.

All - I'm sorry that I sounded arrogant and know-it-all in my post. I don't normally do that. I was feeling a bit proud with my new found knowledge.

I said, "...perfect vapor/air barrier on the warm side of the insulation. This is EXTREMELY important for cathedral ceilings."

This statement is out of context with the discussion of parkpointer's attic. I was just mentioning the fact to whoever might eventually read the thread. It is believed by some that air leaks cause more heat loss from the building envelope than poor insulation. Although it won't help people with a problem, it might help someone before they build. I think my statement applies, regardless of roof/ceiling type, but especially of cathedral ceilings because of limited venting options. Research this subject sometime, it's very interesting.

Rodg
 
 

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