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Old 03-22-2012, 06:42 PM   #1
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I have a feeling my attic doesn't have enough ventilation: today it is 73 degrees out, sunny for half the day and cloudy the rest, and the attic is 87 on the floor, at 6:30pm. The attic is a low crawl-space style, 1300 square feet total. There's a continuous soffit vent, and 2 1 square foot box vents on the higher portions (no gable or anything else). 1 story house, green asphalt shingles. The insulation is pretty thin, but the house is very stuffy when the temperature over 70. Should I install a powered ventilator myself or have a roofer install a ridge vent?

Also, I have a detached, unfinished garage. There's no ventilation in the roof and it gets very stuffy in the summer, especially with the engine heat of the cars. What would be the best way to ventilate this?

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Last edited by matt151617; 03-22-2012 at 06:45 PM.
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Old 03-22-2012, 06:57 PM   #2
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Use a ridge vent not a powered one. It vents 100 of the roof not just a circle, cost nothing to run, and is very DIY.
Why have a roofer install it? A flat bar, ciruler saw and a hammer is all you need.

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Old 03-22-2012, 07:07 PM   #3
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Quote:
Originally Posted by matt151617 View Post
I have a feeling my attic doesn't have enough ventilation: today it is 73 degrees out, sunny for half the day and cloudy the rest, and the attic is 87 on the floor, at 6:30pm. The attic is a low crawl-space style, 1300 square feet total. There's a continuous soffit vent, and 2 1 square foot box vents on the higher portions (no gable or anything else). 1 story house, green asphalt shingles. The insulation is pretty thin, but the house is very stuffy when the temperature over 70. Should I install a powered ventilator myself or have a roofer install a ridge vent?

Also, I have a detached, unfinished garage. There's no ventilation in the roof and it gets very stuffy in the summer, especially with the engine heat of the cars. What would be the best way to ventilate this?

The highlighted statement should have absolutely nothing to do with roof venting.

Oh, yeah, +1 on the ridge vent or add more box vents.

Last edited by seeyou; 03-22-2012 at 07:09 PM.
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Old 03-22-2012, 07:11 PM   #4
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you need insulation and air sealing of the attic floor. Ventilation has nothing to do with the atmosphere of the conditioned space. Ventilation is only to remove excess moisture during the winter months. In your area I would also use a radiant barrier. With poor insulation you are not slowing the heat in the attic from making the house uncomfortable. Solar loading is your cause.
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Old 03-22-2012, 07:27 PM   #5
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Sorry but I'm not a big fan of power vents. Passive venting and insulation, done properly, is all most structures need. Plus they don't cost money to operate and you don't have to wonder if it quit working in a few years.
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Old 03-22-2012, 07:46 PM   #6
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I understand I need more insulation, in some spots there's nothing... the hot air from the attic is leaking into the conditioned space. However, isn't the fact that it's really hot up there a sign of poor ventilation? I was under the assumption the attic should be more or less the outside temperature.

Is a ridge vent really a DIY project? It seems like a good way to cause a leak.
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Old 03-22-2012, 07:47 PM   #7
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The issue with ridge vents is snow gets into it and blocks it. You are better off with the metal ones that look like a mini house. I had some ice dam issues on my roof, mostly with a crappy little vent for the kitchen. Yet my attic vent was untouched. Being on the peak, and about 3 feet high, no snow got into it.

What you do want to check for is that your soffits REALLY are vented. Older houses used to have plywood, then later on they added metal soffit for looks, but did not take out the plywood.

As for DIY, my personal feeling with roofing is to leave it to a pro, but the work itself is really not that hard to do, it's just that if you do end up screwing up, it will do tons of damage. If I had a detached garage or other structure I'd probably DIY with that for practice, but I would not do roofing for my first time on my house.
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Old 03-22-2012, 08:55 PM   #8
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The attic will be warmer than the outside air due to solar loading. Insulation is needed, but air sealing the attic floor is just as important. Ventilation will do nothing to help with your issues.
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Old 03-23-2012, 12:38 PM   #9
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Originally Posted by Bob Mariani View Post
you need insulation and air sealing of the attic floor. Ventilation has nothing to do with the atmosphere of the conditioned space. Ventilation is only to remove excess moisture during the winter months. In your area I would also use a radiant barrier. With poor insulation you are not slowing the heat in the attic from making the house uncomfortable. Solar loading is your cause.
You would use a radiant barrier in NY to correct a lack of insulation?
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Old 03-23-2012, 05:55 PM   #10
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never, R49 is what I put in and R38 is the minimum I would expect. The radiant barrier is above this insulation. And only use blown insulation in an attic. fiberglass batts are near useless in attic floors. email me directly if you need proof or are interested in the scientific reason for this.
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Old 03-23-2012, 06:26 PM   #11
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Use a ridge vent not a powered one. It vents 100 of the roof not just a circle


Matt,

Start with air sealing the attic and adequate insulation as mentioned above. If your roof is low pitched, you said "crawl space style", you may not be able to get as much insulation as needed. Especially near the exterior walls. In that case ventilation will help. Continuous soffit venting and a ridge vent to start. But heavy snow can cover and block a ridge vent in winter. So, if you have ice dam problems, gable vents, one powered in one end and one static at the other, would help with that issue.

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Quote:
email me directly if you need proof or are interested in the scientific reason for this
If there were a scientific reason for this, there should be a published paper or study. Could you post the link to this information?
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Old 03-23-2012, 07:01 PM   #12
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I would have to get back to my office first. Still at the convention in RI. Basically it works like this (and even Owens Corning has confirmed it) below a attic the ceiling is 75 degrees. In the attic it may be 25 degrees. (just a sample) the delta T (change in temperture) creates a pressure that causes a convective loop within the insulation. Now the insulation is not working as planned, since by design this insulation works by little air pockets in the fibers which transfer heat by radiation. this is the slowest method of heat transfer. Slowing transfer of heat at a specific rate yields the R-Value. So the R19 rating under this convection under this type of heat transfer is R2

Also check the chart BPI makes us use to evaluate existing insulation... similar issues are shown

And when trying to get your energy star home using a HERS rating fiberglass does not even count as insulation unless it is sealed on all sides with an air barrier like sheetrock.

fiberglass batts when PERFECTLY installed (rarely happens) works fine if the walls are air sealed and only in walls. The stack effect also is contributing the the pressure that inhibits the batts in a ceiling.

Even in garage ceilings with living space above. The insulation is poor at best. Gravity pulls it down. And fiberglass needs to be completely tight against the warm side of a wall, floor or ceiling to work.
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Old 03-23-2012, 07:09 PM   #13
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Gable vents..... another issue I have. These were invented in 1928 or so to address moisture buildup at the inside surface of roof sheathing. here the 1:3 ratio was established. BUT.... gable vents only work when wind hits that side. this does not happen enough. So along came soffit and ridge vents to the rescue. Now we always have air flow due to physics and not weather. More always moves to less. Gravity creates air stratification pressures. So the higher pressure at the soffit drives air up to the low pressure ridge vents.

Now... many here is disagree and I will allow you all to say what you will since in America we do have the right to be dead wrong.
Gable vents should never be used with ridge vents. It short circuits the air flow. Recommendations are to at least place tyvek or foam board on the inside to block the air if the client wants these for looks.
this too is from building science and most all the writers of Journal of Light Constuction and Fine Home Building are here at this conference today. Every one of the 50 classes is on either moisture control, ventilation, energy efficiency. BPI allows CEU credits for these classes. So this is accepted science. Things need to change. Builders are not building correctly.
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Old 03-23-2012, 09:40 PM   #14
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Quote:
Gable vents should never be used with ridge vents. It short circuits the air flow.
Bob,

Can you show me one study or scientific paper that explains the "short circuit" idea?
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Old 03-23-2012, 09:58 PM   #15
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Bob,

Can you show me one study or scientific paper that explains the "short circuit" idea?
There was actually a graphic on one of the Holmes inspections about this. It works like the chimney effect. That means that air will flow through the path of least restiance. And what is that path you ask? Is from the closest vents to the ridge.

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