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Old 01-16-2008, 10:22 PM  
RickABQ
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Default Attic vents in the dry Southwest

I have a house in Albuquerque, built about 1981. It has what is probably the bare minimum attic ventilation to meet code and I'm trying to figure out how to improve the ventilation so that we extend the life of the roof, make the house more comfortable, and reduce our cooling bills.

The house is a U-shaped ranch, with a pitched, shingled roof. There is a main ridge running from side to side, with two shorter ridges running out the legs of the U. There are gable vents on each of the two ends of the house but not on the gables on the legs of the U so the attic space in the legs is fairly stagnant. One of the gable vents was converted to a thermostatically controlled fan by a previous owner. There are 11 soffit vents around the perimeter.

The rooms in the legs of the U get too warm, I suspect because they get insufficient attic ventilation. I've read a ton of material on the web and concluded that I would improve matters greatly by increasing the soffit vent area by about 3X, installing ridge vents along all 3 ridges, and boarding up the gable vents. However, when I started calling around, I was told that ridge vents are no good because you can't seal them up in the winter! "Gotta keep that attic sealed up tight so you don't lose heat" was the message, along with offers to supply gable vents, powered fans, and wind turbines, all of which can be covered easier than ridge vents.

So, are the contractors I spoke to ignorant, or does the dry climate of Albuquerque change things and we really do need attic ventilation that we can shut off in the winter?

Thanks for any insight.

Rick



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Old 01-16-2008, 10:37 PM  
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Yep, the contractors are ignorant.
The insulation in your ceiling is what keeps the heat from escaping in the winter. (Hey, wait a munute... You guys have winter????)

What you read about the sofit and ridge vents is right on. I don't know about closing up the gable vents, whether that's necessary. I guess it woldn't hurt, but it won't help either.

Picture everything above the ceiling as exterior. You want the tempurature on the underside of your roof the same tempurature as the outside. The way to achieve that is to let any heat that escapes from the interior also escape from the very top of the roof, thus the ridge vent. Heat that get's trapped in your roof does nothing to help keep your living space warn.

By the way, if the builder was that chincy with the roof ventilation, you may want to check how well they insulated the ceilings.



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Old 01-17-2008, 05:55 AM  
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I agree with the ToolGuy... I put additional venting on two roofs now by using ridge vents. One was during a roof replacement and one was just to improve venting on an existing roof. In both cases, I just got out my junk circular saw with a cheap nail cutting carbide blade, snapped two chalk lines- one on either side of the ridge- and started sawing. This left a slot down the ridge. I covered the slot with a commercially available ridge vent. I've seen two common types -- one that is made from plastic that is crosshatched with material to make it difficult for things(rain & bugs) to work their way back up the ridge into the attic. The second is a woven type of material that air can flow through. You just bed the section over the slot in the ridge and nail or screw it down. Then you cover with shingles or whatever roofing material you're using.

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Old 01-17-2008, 06:19 AM  
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ToolGuy,

Yes we have winter! Albuquerque is not Phoenix, we're at 5000-6000 feet elevation and it gets cold here. It's 11 degrees F as I type but will warm up to 40 this afternoon ... And we do get snow, though not too much. It's very dry though. So dry that we run humidifiers constantly.... causing moisture to seep into the attic! Hmmmm.... I see the problem...

The idea of covering up the gable vents is so that the outlet vents are all at the same height so the airflow sweeps the whole attic. The greater the vertical distance between inlet and outlet, the greater the chimney effect and the greater the airflow. The gable vents are a good 3-4 feet lower than the ridge and so might actually result in less net airflow, and in a less desirable pattern. Plus with proper ventilation installed elsewhere, I'm afraid the gable vent fan would disrupt my desired airflow, while continuing to cost money to operate. What do you think?

This 20-page booklet is where I learned the most: http://www.airvent.com/pdf/literature/PAVbooklet.pdf (but it doesn't specifically address whether anything is different in a very dry climate).

So if the roofing contractors I spoke with are ignorant, what kind of contractor knows this stuff and can design a good system?

Thanks!

Rick

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Old 01-17-2008, 06:34 AM  
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You are in the right neighbor hood. I have been to your town ...on a convention in your city. Nice balloon festival.
Close up the gable vents and go with the soffit and ridge vent. You will be fine. Insulate the attic and make sure you have a vapor barrier facing the interior ceiling. You are in a cold climate...just dryer than most.
You answered your own questions...way to go.
A good insulation contractor can be of help with the attic ventilation issues.

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Old 01-17-2008, 07:09 AM  
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It sounds like you should be more concerned with insulation and more cooling than venting.

The contractors probably sounded ignorant because they dont think it is necissary. The whole reason you are doing this is because your "leg rooms are too hot". These rooms have 3 exterior walls ,probably with alot of windows, so keeping them heated and cooled will be harder compared to the main house. The cooling system may have not be designed to compensate for this enough. This can be probaby can be fixed alot cheaper and easier than what you want do with the venting. Check the insulation in the ceiling if you can see the rafters then you should add more.
If you are still worried about venting try getting one of those wireless themomiters. Instead of putting the sensor out side put it in your attic and you can monitor the temp up there move it around and you will get a good idea of how bad your venting is. remember though there is no amount of ventalation that will cool your attic to outside temp with the sun is baking your house. fans are needed to combat this. so rely more on the attic temps early in the morning before sunset.

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Old 01-17-2008, 07:33 AM  
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i would highly suggest putting a roof mounted themo. fan with or without add ridge vents.

some other cooling tips would be to add or close your window coverings. The sun shining through your windows do alot to heat up your room.

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Old 01-17-2008, 08:10 AM  
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Quote:
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..............If you are still worried about venting try getting one of those wireless thermometers. Instead of putting the sensor out side put it in your attic and you can monitor the temp up there move it around and you will get a good idea of how bad your venting is. remember though there is no amount of ventilation that will cool your attic to outside temp with the sun is baking your house. fans are needed to combat this. so rely more on the attic temps early in the morning before sunset.
I did exactly this in Michigan. I find that my attic (just above the insulation) runs about 1 to 2 degrees warmer than the outside temperature, at night, in winter. I have not yet gone through a summer with the thermometer but I know from sticking my head up in the attic it gets very hot in summer.

I'd recommend the OP do this as well. You can buy wireless thermometers for $15, or less on sale.
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Old 01-17-2008, 03:42 PM  
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Welcome Rick:
I'm so glad you mentioned sealing up vents for the winter. I think the whirly-bird vents look soooooo stupid with a garbage bag over them. The attic ventilation should be for the full year-around, hot or cold.
The soffit vents and ridge vent are the best in my experience. They give you something close to the 'ice house' effect, keeping the lower side of the shingles a little cooler in the summer.
Your gable vents won't hurt a thing but I am like you; I would not run the fan.
Glenn

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Old 01-17-2008, 10:02 PM  
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Quote:
Originally Posted by RickABQ View Post
ToolGuy,

Yes we have winter! Albuquerque is not Phoenix, we're at 5000-6000 feet elevation and it gets cold here. It's 11 degrees F as I type but will warm up to 40 this afternoon ... And we do get snow, though not too much. It's very dry though. So dry that we run humidifiers constantly.... causing moisture to seep into the attic! Hmmmm.... I see the problem...

The idea of covering up the gable vents is so that the outlet vents are all at the same height so the airflow sweeps the whole attic. The greater the vertical distance between inlet and outlet, the greater the chimney effect and the greater the airflow. The gable vents are a good 3-4 feet lower than the ridge and so might actually result in less net airflow, and in a less desirable pattern. Plus with proper ventilation installed elsewhere, I'm afraid the gable vent fan would disrupt my desired airflow, while continuing to cost money to operate. What do you think?

This 20-page booklet is where I learned the most: http://www.airvent.com/pdf/literature/PAVbooklet.pdf (but it doesn't specifically address whether anything is different in a very dry climate).

So if the roofing contractors I spoke with are ignorant, what kind of contractor knows this stuff and can design a good system?

Thanks!

Rick
I guess my ignorance lies in geography - any place south of me I just assume is warmer. But wow, that sound's like Chicago weather!

What you say about the gable vents makes sense. I'm still in the learning myself, just know that ridge and sofit vents are almost always a good thing. As for ignorant roofers, all I can suggest is to call others. Surely some of the homes in your area have ridge vents, and so somebody there installs them. Wish I could be of more help.


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