# Attic venting questions



## Grumpy (Dec 12, 2003)

On roofs like this I almost never spec ridge vent. Look into solar powered attic fans. I have used air vent, which are 880 cfm, 55% more powerful than the GAF solar fans. 


It is not a myth. Where do yout hink the fan will pull air? The path of least resistance. That often means the closest opening, that closest opening is likely the ridge vent 2' away from the fan which leaves 98% of your roof unvented.


----------



## lemmy (May 18, 2011)

I saw a video of an attic filled with smoke and it had a ridge vent and an attic fan. The smoke really wasn't moving much at all until the fan kicked on. When it did all of the smoke in the attic started moving toward the fan. It seems that if the fan was pulling from the ridge vent, the smoke wouldn't have moved at all. This and other posts I have read from people way more knowledgeable on the subject than I am is why I referred to it as a possible myth. Also, regardless of how much is being pulled in from the ridge vent, hot air will rise. If the air in the attic is not being ventilated, it will be getting hot and sooner or later it will rise up to the top and mix with the air that is being pulled out by the fan. 

It seems that many people recommend solar powered fans. Is that because of the energy they save, or because they will run pretty much all day?


----------



## Grumpy (Dec 12, 2003)

I don't know what dis-information you got from proclaimed experts. I have been a roofer for 13 year and have really been studying attic ventilation for the past 10. I have been arguing with guys about ventilation on these forums since I began studying it. The ammount of "I do it my way" and "I know more than the manufacturer" that is out on the internet is staggering. You may find "guys" saying it's ok, but show me just one fan or ridge vent manufacturer who approves or encouraged the use of fans in conjunction with other vents (excluding intake) and I will forever denounce the short circuit theory. I, or anyone, can do and say what ever I want, that doesn't make it true. As a professional roofing contractor it is my obligation and duty to install the products that I do install to the instructions and methods as prescribed by the manufacturer of said products. Doing otherwise I assume risk and liability and most of all risk wallowing with the trunk slammers and hacks that do what ever they feel like.

I admit I am not an engineer. I have not spent thousands of dollars building test houses to perform an independant study to prove nor disprove the theory. But I do what the product engineers who have done the calculations and studies tell me to do. Simply taking the time to read installation instructions would eliminate this argument all together.



I recommend solar fans in retrofit applications because they require no wiring. I am not a licensed electricin and my insurance exlcuds electrical related activities. Therefore running a circuit up from your breaker is not something we are qualified to do. Getting an electrician involved will cost a few hundred bucks to a few thousand bucks. From a pure economical point of view, solar fans are much cheaper to install when no fans already exist.

The running all day thing is also an added benefit, especially in winter. Most attic fans unless they have a humidistat will not operate at all in winter, but attic ventilation is equally as important in winter as it is in summer. Most traditional hard wired attic fans don't have humidistats because they cost extra money. People are often inherintly cheap.

The money a solar fan saves on electricity is also a bonus. And the money you get tax back is certainly an incentive.

The cons to solar fans is that a solar fan costs more than a traditional hard wired fan, but not that much more, maybe $100 more than a similiar powered wired fan. The other con is that no solar fan is as powerful as the average 1100CFM wired attic fan. 1100 CFM or very close to it is pretty much the standard, although I have installed larger and smaller wired fans. This means you often need more fans. The cost thing really isn't a factor on retrofit applications because of the electrical scenario described above.


----------



## texasprd (May 14, 2011)

I hope I'm not hi-jacking the thread with this question - in a hot climate such as S. Texas/Arizona/Nevada, using solar-powered roof fans, wouldn't there be an issue with residual heat once the sun goes down and the fans stop?


----------



## Grumpy (Dec 12, 2003)

The solar fans will still allow air to ventilatewhen the sun goes down. Though they would then become passive instead of active, very much like a large mushroom/breather vent. 

There is a product that I know of that turns a solar fan into a hybrid solar/electric fan. However it then requires wiring.


----------



## seeyou (Dec 12, 2008)

lemmy said:


> I saw a video of an attic filled with smoke and it had a ridge vent and an attic fan. The smoke really wasn't moving much at all until the fan kicked on. When it did all of the smoke in the attic started moving toward the fan. It seems that if the fan was pulling from the ridge vent, the smoke wouldn't have moved at all. This and other posts I have read from people way more knowledgeable on the subject than I am is why I referred to it as a possible myth.* Also, regardless of how much is being pulled in from the ridge vent, hot air will rise. If the air in the attic is not being ventilated, it will be getting hot and sooner or later it will rise up to the top and mix with the air that is being pulled out by the fan*.
> 
> *It seems that many people recommend solar powered fans. Is that because of the energy they save,* or because they will run pretty much all day?



You are correct about the "short circuiting". If it does occur, heated/moist air is still being exhausted, just maybe not quite as efficiently as it would be if short circuiting did not occur. 

My primary concern with power vents is that if there are any breaches in the envelope between the conditioned space and the attic space, conditioned air can be pulled from the living space into the attic, which is a very undesirable side effect.

So, before installing a power vent, air sealing is necessary as is making sure there is adequate intake. If there is plenty of intake to satisfy the power vents pull, then short circuiting through gable or ridge vents already in place should be minimal. 

The problem with solar powered fans, IMHO, is the initial expense and they quit running at sundown. There's usually still a lot of stored heat in the structure that needs to be exhausted after sundown.

Power vents can be very effective at attic cooling, but a properly designed static system can as well. The smoke test video offers up some real information, but every instance is not equal to the situation shown. I use power vents only as a last resort. 

If you have a problem with heat transferring through the ceiling, then you have inadequate or improperly installed insulation. Trying to cool the inside of the house down by sucking hot air out of the attic is treating the symptom, not the disease. 

If you have a moisture problem in the attic, then you certainly need more/better venting, but you are only going to get the attic temperature down so far on a hot, sunny day, no matter how or how well the attic is vented.


----------



## seeyou (Dec 12, 2008)

Grumpy said:


> I don't know what dis-information you got from proclaimed experts. I have been a roofer for 13 year and have really been studying attic ventilation for the past 10. I have been arguing with guys about ventilation on these forums since I began studying it. The ammount of "I do it my way" and "I know more than the manufacturer" that is out on the internet is staggering. You may find "guys" saying it's ok, but* show me just one fan or ridge vent manufacturer who approves or encouraged the use of fans in conjunction with other vents (excluding intake) and I will forever denounce the short circuit theory.* I, or anyone, can do and say what ever I want, that doesn't make it true. As a professional roofing contractor it is my obligation and duty to install the products that I do install to the instructions and methods as prescribed by the manufacturer of said products. Doing otherwise I assume risk and liability and most of all risk wallowing with the trunk slammers and hacks that do what ever they feel like.
> 
> I admit I am not an engineer. I have not spent thousands of dollars building test houses to perform an independant study to prove nor disprove the theory. But I do what the product engineers who have done the calculations and studies tell me to do. Simply taking the time to read installation instructions would eliminate this argument all together.
> 
> ...



Those are some excellent points about the solar vents. 

I prefer not to install power vents except as a last resort, but I have not been able to find any product literature that says *NOT* to combine passive and powered exhaust. I can find a lot of opinion about the subject on about every forum that exists, but no manufacturer's recommendations. You are correct that there are no recommendations to use the two together, but I'd like to see some product specs/literature/instructions, that says specifically not to combine the two if you have it.


----------



## Grumpy (Dec 12, 2003)

seeyou said:


> but I have not been able to find any product literature that says *NOT* to combine passive and powered exhaust. I can find a lot of opinion about the subject on about every forum that exists, but no manufacturer's recommendations. You are correct that there are no recommendations to use the two together, but I'd like to see some product specs/literature/instructions, that says specifically not to combine the two if you have it.


Here you go:


AirVentInc. said:


> Can I install a power fan if I have a ridge vent already on my roof?
> Mixing a power vent with a ridge vent can short-circuit the attic ventilation system just as a gable vent can as discussed above. This happens because air follows the path of least resistance. When the power vent turns on, it can pull air from the ridge vent, which could lead to weather infiltration and unbalanced airflow along the underside of the roof deck. When the power vent turns off, it acts like a roof louver — an opening on the roof without a motor. In this scenario, the ridge vent pulls its intake air from the power fan leading to possible weather infiltration and less than optimal ventilation along the underside of the roof deck.
> 
> Basically, mixing two different types of exhaust vents on the same roof that has a common attic is not recommended because it can lead to short-circuiting of the attic ventilation system.


taken from: http://www.airvent.com/professional/resources/troubleshooting.shtml 

It's also found in their ventilation education certification found here: http://www.airvent.com/professional/vip.shtml

Not only have I gone to their seminars every other year, but I have also completed both certifications for specifiers as well as installers. I have also required my employees to get certified with Air Vent as well. 



I am currently negotiating with another solar fan manufacturer to become one of their dealers as well as their exclusive certified installer for the Northern IL area.


----------



## seeyou (Dec 12, 2008)

Thanks. 

I notice that they're very careful to say "CAN" vs "WILL" short circuit.

I still think that if there's proper inlet, in most cases, short circuiting will be fairly inconsequential. Not saying it doesn't happen, but I think the real myth is that air will enter a gable or ridge vent and exit through a power vent without picking up some heat or moisture. Will that path be as efficient as entering at a lower point? Absolutely not, but it doesn't seem to me to be the problem some think it is. 

Now, FWIW, I've installed maybe 10 power vents total in about 30 years of roofing, so I'm not advocating mixing power vents with other types of outlet and I don't have encyclopedic knowledge of them. 

I've seen smoke tests done inside the living space when a power vent is running with "assumed" adequate intake. Lots of smoke can get sucked through the penetrations in a ceiling. So, given the options, I'd rather see some air pulled in a ridge vent than pulled from around a can light.


----------



## handy man88 (Jan 23, 2007)

What so bad about "short circuiting?" It's not like the hot air in the attic is not escaping just because the ridge vent is being used as a soffit vent.  

The draw from this exit flow will pull the hot air out also, as it rises, and faster than natural convection.


----------



## Grumpy (Dec 12, 2003)

Copper, the answer to fans pulling from light fixtures is not to install a ridge vent as an intake but to install some form of intake as an intake and better seal the fixtures. 

Mixing a roof fan with gable vents doesn't bother me so much when there is no intake. However mixing let's say a gable fan with a ridge vent is just dumb because it'll pull air strictly from the ridge vent and not the corresponding gable vent. 

What's so bad handy man is two things. 1 if I do it according to specification I can bever be blamed should there be a mold, condensation, premature shingle failure or other ventilation related problem. The problems that result from poor ventilation are numerous. I have substantial and documented proof that I did my work according to specification which is my job and was what I was hired to do. This is the reason I try to always do everything that I do to specification. If there is a problem and I did something the manufacturer said not to do, guess who is now at fault? Me. When customers insist on me going agains spec, I always make them sign a disclaimer. This would be one of those instances. 

Liability aside. You're right if you want to split hairs. The attic ventilation will be more effecient than passive vents or as you put it natural convection, even if the fan pulls some air from the ridge vent. But let's be honest the fan would be much much more effecient if the ridge vent were not there for the fan to pull air from, and the fan were pulling air from proper intake at or near the overhangs. So what you are saying is that the ventilation will still work, and I agree. What I am saying is the ventilation will work BETTER, and for some reason people refuse to agree.


----------



## lemmy (May 18, 2011)

Any recommendations on a solar fan? I have found an attic breeze model that is 1350-1550 CFM. Do the solar fans last as long as the electric ones? 

my house is already wired for a powered fan so electrician cost really isn't an issue.

I haven't lived in this house very long. Only a couple of months. The roof was 17 years old and was recently damaged by hail. So it is getting replaced and I really don't know if there were problems or not. The roof was in ok shape but needed replacing fairly soon before the hail damage. So I assume whatever ventilation system that was in place was working ok. 

I plan on sealing my house (top cap and canned lights) as much as I can. But I can't get to the top of some of the lights because it is a cathedral ceiling in areas. however my one concern with a solar powered fan is that it would run even more than an electric one so it seems it would suck even more air conditioned air from the house than an electric one (given the same CFM).


----------



## seeyou (Dec 12, 2008)

*the answer to fans pulling from light fixtures is not to install a ridge vent as an intake but to install some form of intake as an intake and better seal the fixtures. 

Mixing a roof fan with gable vents doesn't bother me so much when there is no intake. However mixing let's say a gable fan with a ridge vent is just dumb because it'll pull air strictly from the ridge vent and not the corresponding gable vent.*

Grumpy, we're pretty much in agreement here. The point I'm trying to make above all, is that there is no one answer to attic ventilation. My concern is those who would install a power vent without adding adequate intake (and that's advice frequently given on this forum) and air sealing the living space. Adding a power vent to counter inadequate insulation is also foolishness, IMHO. 

A seasoned pro such as yourself is able to quickly and accurately assess a situation in person and arrive at the best solution. Since attic venting questions are asked so often on this forum, it seems like we ought to come up with a check list of questions for the person with a hot attic to ask themselves. Anyone please feel free to add or subtract and maybe we'll start a new thread to refer to when we get the check list finished.

1) type or roof - hip, gable, flat
2) slope
3) roof material
4) attic sq feet
5) type/thickness of insulation
6) has the living envelope been air sealed?
7) does the house have soffits and are they currently vented? If so, describe vents, quantity and size.
8) existing roof venting - describe - quantity and size
9) what am i forgetting?


----------



## seeyou (Dec 12, 2008)

lemmy said:


> Any recommendations on a solar fan? I have found an attic breeze model that is 1350-1550 CFM. Do the solar fans last as long as the electric ones?
> 
> my house is already wired for a powered fan so electrician cost really isn't an issue.
> 
> ...


There are several available caulks and foams to seal around the perimeter of can lights as well as bulb baffles that will greatly reduce the infiltration through the cans for situations like you describe. The top plate where wires and pipes penetrate is also an area of concern.

What I've read on several solar fan sites is that since the solar units are less powerful, they would in theory create less depressurization of the attic than a hardwired unit. So, in theory, the solar fan is running constantly at a lower rate, creating less interior suck. The hardwired unit is running hard, cutting off, running hard, cutting off. However, real life experience tells me that on a fairly warm, sunny day, the hardwired unit is not going to cut off very often.


----------



## seeyou (Dec 12, 2008)

Hey Grumpy - 

I ran across this and thought you might be interested:

*Angela of Houston, TX writes...*
_"I have heard good things about Attic Breeze from one of my neighbors that has installed your solar attic fans. I would like to install a solar attic fan on my home as well, but my roof has ridge vents and I am concerned that these may not work well with the fan. Can your solar attic fans be installed on a home that has ridge vents?"_

Yes, you may install our products with an existing ridge vent. However please note that while the solar attic fan is operating, the ridge vent will work in reverse acting as air intake vent. In fact, every passive vent on your roof will act as an air intake vent while the fan is operating. This is not a problem, it is simply a different method of operation for your roof's ventilation system.

Ridge vents operate on the principle of natural draft air convection. This means that as the attic heats up, hot air will rise to the attic ridge and naturally flow out from the ridge vent. For ridge vents to work properly, the attic temperature must be in the range of 130-140°F. During normal operation, ridge vents typically produce 3-4 attic air exchanges per hour, not enough to adequately cool the attic and minimize heat transfer into your home.

_Attic Breeze_ solar attic fans operate on the principle of forced draft air convection. Our fans create an air draft through the attic many times more powerful than that of natural draft air convection or wind powered turbine vents. _ Attic Breeze_ solar attic fans work the hardest when you need them the most creating a self-regulating ventilation system; the more solar radiation (sunlight) your roof receives, the faster our solar attic fans operate to remove heat. During normal operation, _Attic Breeze_ solar attic fans have the capability of exchanging hot attic air 10-20 times per hour, typically keeping your attic temperature between 5-15°F of ambient outside temperature. 

When installing our products in conjunction with ridge vents, the solar attic fan unit should be installed a minimum of 5-6 feet away from the ridge vent to allow for balanced air flow through the attic. Experience shows that this distance will typically allow enough space for proper balancing of air intake ventilation from both the ridge vent and other roof vents. When the solar attic fan is not operational, the ridge vent will function as normal.


----------



## lemmy (May 18, 2011)

I notice that on my old house. It comes on and runs all day. 

One thing I don't understand about the solar units is that they will claim a 25W unit and something like 800-1000 CFM. Then a wired unit that consumes 200-300W is about the same or not much more. Are the solar units playing some trickery with the numbers?


----------



## lemmy (May 18, 2011)

I have thought about removing the ridge vents that are near the two existing fans and let the fans do the work. (they are less than the 5-6 feet away) but then keeping the ones on the other sections of the house that are over small sections with no much attic area (where the insulation baffles have to be used because the ceiling is so close to the rafters). One example is the long red line I drew in the picture.


----------



## Grumpy (Dec 12, 2003)

I haven't looked at the wattages on the Airvent Solarcool fan, but they rate at 880. I have never seen another solar fan rated higher than 880, but I haven't much looked either. Gaf is rated at 550 for their solar fan. Up until about last year these were just about the only players on the market in my area. 

I can tell you from experience that the solar fan moves noticeably slower than a wired fan. I really have no way of measuring if the fan rated at 880 is really 880 other than trusting the literature is correct and assume it's been on the market long enough someone would have busted them by now. 

I'm not going to argue any more about intake or exhaust or short circuiting. I have stated my reasons for not doing it. I stand by my decisions.


----------



## texasprd (May 14, 2011)

Grumpy said:


> The solar fans will still allow air to ventilatewhen the sun goes down. Though they would then become passive instead of active, very much like a large mushroom/breather vent.


But in that situation, would they have sufficient NFA? It seems unlikely to me. And because there would be fewer vents, wouldn't that result in uneven ventilation (though maybe it wouldn't be significant)? It does stay quite warm in the attic after a 100+ day, and I'd want to be sure that heat would have enough ventilation.

Just trying to think this all the way through and look at as many factors as possible - thanks for all the info so far!


----------



## [email protected] (Nov 17, 2008)

> I don't know what dis-information you got from proclaimed experts. I have been a roofer for 13 year and have really been studying attic ventilation for the past 10.


Are you saying you are giving dis-information, or are not an expert?:whistling2:

There are seminars where you can learn to earn a billion dollars in real estate with no money down...*if you buy their product*.

Think about this, if you direct a vacuum hose towards a pile of dust, what happens? 
Unless that ridge vent is directly in front of the power fan, it's not the path of least resistance.


In the absence of any evidence ( real evidence, not a line from a brochure) to the contrary, I'd go with the information presented here; http://www.roofingcontractorreview.com/Roofing/Attic-Ventilation/Roof-and-Attic-Ventilation.html


----------



## Grumpy (Dec 12, 2003)

That's great, you can do it your way and i will do it my way, the way the manufacturers instruct. If nothing goes wrong for you, awesome. If anyone goes wrong for me I am covered by the fact that I did my job to the best of my ability and didn't reinvent the wheel or claim to know more than the inventors of the products I am installing. When something goes wrong and you installed the fan/material against manufacturer specs, guess what: YOU ARE LIABLE. This is true of all products, not just fans. So, please have a 

I'm guessing you are Dennis I have conversed with you for years on the various forums as a matter of fact. I can put up a website exactly like this one but claiming the opposite, but to what gain? Your comment about the brochure holds true in this regards as well. Just because YOU built a website with an opposite opinion of mine doesn't make your OPINION any more valid than mine. As for the videos, if I see those studies performed on real properly constructed full size houses, my opinions may be swayed. However on cardboard tests houses, it seems more like arts and crafts and practice making a video than any sort of scientific study. I said that a yer or two ago when you first posted the videos at CT or NRG, I forget which. 

Though even if my opinions are swayed, for liability reasons, I will still always install the productsin the means that the manufacturers of the products say. 

So again Please have a day and go play with some construction paper and elmers school glue some more. Don't ever come trolling infering that I am some kind of hack giving dis-information. I won't stand for that. On every job I do, I always try to do the job to the best of my ability. I am not always right, nobody is, but I always try. For someone to claim the opposite, well that's just real EZ to do on the Internet, isn't it?


----------



## Grumpy (Dec 12, 2003)

texasprd said:


> But in that situation, would they have sufficient NFA? It seems unlikely to me. And because there would be fewer vents, wouldn't that result in uneven ventilation (though maybe it wouldn't be significant)? It does stay quite warm in the attic after a 100+ day, and I'd want to be sure that heat would have enough ventilation.
> 
> Just trying to think this all the way through and look at as many factors as possible - thanks for all the info so far!


As stated I have seen hybrid solar electric fans. Maybe one fan is not enough, there are calculations you can make which will determine how many vents, fans, etc... you will need. 

Then again if you have a wired attic fan without a humidistat also installed, you have the same concerns in winter time about the minimal NFA. You're not just trying to vent heat from the attic, but also moisture which is as much of a problem in winter as it is in summer. There are pros and cons to everything.


----------



## lemmy (May 18, 2011)

If you were installing an Attic Breeze solar attic fan would you follow that manufacturers' recommendation that is ok to have one of their attic fans with a ridge vent?


----------



## seeyou (Dec 12, 2008)

Pass the popcorn............


----------



## lemmy (May 18, 2011)

I really didn't mean that to be disrespectful to Grumpy. I genuinely respect his opinion and I am just asking what he would do in that case. I know less about this than anyone that has posted in this thread and the only way to learn is to ask questions.


----------



## handy man88 (Jan 23, 2007)

I considered a solar powered attic fan until I found out that I would need to install more than 2 in order for it to be adequately sized for my attic (not just an additional cost, but an additional penetration through the roof). 

Couple that with the fact that these fans shut off after sunset, I decided to go with an AC powered power vent with an on/off switch in the living space. My power vent has both a thermostat and a humidistat, but I have shut the humidistat feature off.

I have noticed that the 2nd floor is not as hot compared to pre-power vent. Also, I have about a R-55 of insulation in the attic.

It is deathly hot in the attic during the warm months. I've felt sweat come out of the pores of my hands when I was up in there in the past. The rafters were even hot to the touch.

If you insist on installing a power vent, but are concerned about "short circuiting," you could always have the ridge vent closed. The only issue is that during the winter, if you live in a cold climate area, you would be relying on the power vent hole (without the fan turned on) for hot air to escape. 

Also, if you close off that ridge vent and your power vent dies, then the heat will also only be able to escape though that penetration.


----------



## [email protected] (Nov 17, 2008)

Grumpy.



> That's great, you can do it your way and i will do it my way, the way the manufacturers instruct. If nothing goes wrong for you, awesome. If anyone goes wrong for me I am covered by the fact that I did my job to the best of my ability and didn't reinvent the wheel or claim to know more than the inventors of the products I am installing. When something goes wrong and you installed the fan/material against manufacturer specs, guess what: YOU ARE LIABLE. This is true of all products, not just fans.


I've also been known to stand on the top step of a step ladder.



> So, please have a day.


:huh: Sorry, I don't do acronyms or text. What does that mean?



> I'm guessing you are Dennis I have conversed with you for years on the various forums as a matter of fact. I can put up a website exactly like this one but claiming the opposite, but to what gain? Your comment about the brochure holds true in this regards as well. Just because YOU built a website with an opposite opinion of mine doesn't make your OPINION any more valid than mine. As for the videos, if I see those studies performed on real properly constructed full size houses, my opinions may be swayed. However on cardboard tests houses, it seems more like arts and crafts and practice making a video than any sort of scientific study. I said that a yer or two ago when you first posted the videos at CT or NRG, I forget which.


You could build a website and claim the opposite, but you would have nothing to back it up. 
You have heard of scale models and wind tunnels, yes? 
If you look through the website, you would also see videos of tests done inside real attics. Have you ever tested your vents once installed?



> So again Please have a day and go play with some construction paper and elmers school glue some more. Don't ever come trolling infering that I am some kind of hack giving dis-information. I won't stand for that. On every job I do, I always try to do the job to the best of my ability. I am not always right, nobody is, but I always try. For someone to claim the opposite, well that's just real EZ to do on the Internet, isn't it?


*Your* quote from *your* first post;


> I don't know what dis-information you got from proclaimed experts. I have been a roofer for 13 year and have really been studying attic ventilation for the past 10.


So
A. You are calling me a hack.
B. You are calling us both hacks.
C. You are an "expert" who knows more than a "proclaimed (?) expert".

Which is it?


So please, have a "righteous indignation" kind of day.


----------



## Grumpy (Dec 12, 2003)

Never once did I claim to be an "expert". Read my postings about attic ventilation and show me once where I said "I am an attic ventilation expert." What I did say: I said I have attended seminars. I have said I have studied ventilation for 10 years. I said I have completed various certifications. I also said I am not an engineer. I also said I didn't design or develope the specifications. 

The information I have comes from the manufacturers of the products I installed. That's what's "backing me up". You may gamble with the houses of your customers on some quest to prove "the man" wrong, but I prefer to leave my gambling for the casino not the homes of my customers. 

Have I tested some of the ventilation systems I have installed? Yes over the last several years I have had the opportunity on occasion to test some. In most cases there has been no need because <gasp> I did it right the first time.


----------



## federer (Aug 20, 2010)

Grumpy if I may ask then- what about for the new types of roofing where they close off the soffits and ridge vents, spray foam the deck, and condition the attic space instead. then no ventilation is required, correct?


----------



## handy man88 (Jan 23, 2007)

federer said:


> Grumpy if I may ask then- what about for the new types of roofing where they close off the soffits and ridge vents, spray foam the deck, and condition the attic space instead. then no ventilation is required, correct?


That's just another area in the house that will be conditioned, but will not be used. I would venture to say that your HVAC system wasn't sized to factor in this entirely new area.

Also, I would venture to say that the roof sheathing will be taking a beating.


----------



## seeyou (Dec 12, 2008)

*That's just another area in the house that will be conditioned, but will not be used. I would venture to say that your HVAC system wasn't sized to factor in this entirely new area.

*That's typically not an issue. While more cubic feet of space to be conditioned is added, it's easier to condition the total space due to higher R value and less convection that results from using foam products VS fiberglass.


----------



## Gary in WA (Mar 11, 2009)

Conditioned attics: http://www.buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates

http://docs.google.com/viewer?a=v&q...iYVZpx&sig=AHIEtbRVXHNlbPlXiHMzGIwFLQF3YvmyFw

http://www.buildingscience.com/documents/reports/rr-1001-moisture-safe-unvented-wood-roof-systems

Solar fan payback years: http://www.fsec.ucf.edu/en/publications/html/FSEC-GP-171-00/

http://epics.ecn.purdue.edu/hfh/_team_documents_web/02_SolarProject_Results/solarresults.htm

Dangers of powered vents; http://www.advancedenergy.org/buildings/knowledge_library/ventilation/Attic%20Ventilation%20Case%20Studies.pdf

Page 85: http://books.google.com/books?id=Eq...+vents&lr=&as_brr=3&cd=33#v=onepage&q&f=false

http://www.ronhungarter.com/black_mold.html

The foam board may need to be covered: 4.2.1.2: http://building.dow.com/ee/pdf/ESR-2142.pdf

Just a few sites I found interesting. Let's keep on topic please.

Gary


----------



## federer (Aug 20, 2010)

handy man88 said:


> That's just another area in the house that will be conditioned, but will not be used. I would venture to say that your HVAC system wasn't sized to factor in this entirely new area.
> 
> Also, I would venture to say that the roof sheathing will be taking a beating.


thanks for the reply. i did not specifiy but in my case there is no attic actually it's completely built in as bedrooms so the space is being used completely. the ceiling of the bedroom is essentially just like 8in from the roof decking.


----------



## lemmy (May 18, 2011)

GBR in WA said:


> Conditioned attics: http://www.buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates
> 
> http://docs.google.com/viewer?a=v&q...iYVZpx&sig=AHIEtbRVXHNlbPlXiHMzGIwFLQF3YvmyFw
> 
> ...


Good links. But basically if you follow their recommendations then it is impossible to ventilate my roof. Not enough room for continuous ridge vents. Even if you put ridge vents on all ridges, they are at different levels so they would just short circuit each other (if you follow their logic). So you get rid of ridges and put 5-6 fans on the roof and that is dangerous and also very inefficient. My existing roof is 17 years old (with a 20year shingle) and has two powered attic fans and several short ridge vents. So my attic should be full of mold, it should be 160 degrees, everyone that ever lived in it should have died from CO and the A/C cost should be enormous. However, I see no signs of moisture or mold, and I don't think anyone has ever died in the house from CO.


----------



## handy man88 (Jan 23, 2007)

lemmy said:


> Good links. But basically if you follow their recommendations then it is impossible to ventilate my roof. Not enough room for continuous ridge vents. Even if you put ridge vents on all ridges, they are at different levels so they would just short circuit each other (if you follow their logic). So you get rid of ridges and put 5-6 fans on the roof and that is dangerous and also very inefficient. My existing roof is 17 years old (with a 20year shingle) and has two powered attic fans and several short ridge vents. So my attic should be full of mold, it should be 160 degrees, everyone that ever lived in it should have died from CO and the A/C cost should be enormous. However, I see no signs of moisture or mold, and I don't think anyone has ever died in the house from CO.


Yup. Information suffocation.

No diss on anyone, but the more you read on everyone's opinion/information on the internet, the more you head towards irrational panic.


----------



## federer (Aug 20, 2010)

regardless I think GBR is a great resource on the forum.


----------

