Roof venting


  #1  
Old 01-26-06, 05:23 AM
sitedrifter
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Roof venting

I am getting ready to have a roof put on and the contractors are all split on how to vent the roof.

1. 50 percent say:

no ridge vent
2 power vents
leave the vents on the sides of the house (the ones at the peak on the sides)

2. 25 percent say

ridge vent
remove power vent
close up vents on side of house (since the air will be drawn form the soffit vents)

3. 20 percent say

ridge vent
leave vents on sides of house
remove power vent

4. 5 percent say

ridge vent
leave vents on sides of house
leave power vent


I am also leaning towards owens corning fiberglass shingles.
Too me, #3 looks like the way to go but I am not sure (neither are most of these guys) and would love any help you can give on this.


Thanks

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  #2  
Old 01-26-06, 05:46 AM
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Location, location, location

The answer partly depends on where your house is. If it is in the snowbelt, then I would recommend passive ventilation, soffit to ridge with no side vents. If you're in the warm areas, a heat or humidity-activated power vent with soffit feed (air intake) and no side vents would be good. If you are in heavy snow country, then ridge vents may not work well, and you will be better off with soffit feed and side vents.

The answer also has to take into account the slope of the roof, and whether the air flow inside the attic encounters many or few obstructions. If you have cathedral ceilings, then another set of answers become appropriate.

When discussing roofing ventilation, you focus on the following:
1 - an effective and leak-proof vapour barrier,
2 - adequate amount of intake (usually along soffit) at lower edge of roof,
3 - an unobstructed path from intake into the attic (also known as the air channel),
4 - adequate mount of outlet (ridge vent or other), located as high on roof as possible
5 - adequate insulation for your area (to minimize heat loss into attic when cold and heat gain from attic when hot)

"Adequate" usually means having a ratio of 1:150 in terms of ventilation area compared to attic area (although the code in most areas requires a minimum of 1:300), with the ventilation balanced 50/50 between intake and exhaust. Combining ridge vents with side vents is usually not recommended since you want air flow from the lowest parts of the roof, and side vents end up short-circuiting the airflow (there is less air resistance to get the air from the sides than from the soffits).

Hope this helps...
 
  #3  
Old 01-26-06, 06:47 AM
sitedrifter
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Good information. Thanks

A little more on my house and location:

NJ.. Cold and wet in the winter and hot and humid in the summer

Soffit vents on my house may not even be that functional since the insulation goes all the way to the soffit area and there is no rigid foam on the interior of the roof that goes to the soffit area and up the sheating. (house is 30 years old)

Any suggestions with this setup?


Thanks again for your great info

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  #4  
Old 01-26-06, 08:11 AM
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Ventilation... Continued

To see if your soffit ventilation is effective, one way is to get into the attic, turn off all lights, and see if you can see any light shining up from the soffits. If it's dark all around, you do not have effective ventilation. To fix, you start at the soffit and see if there is any wood just behind the soffit blocking the airflow. If yes, remove. Next, above the soffit you will have a cavity, sometimes blocked by insulation. If yes, remove. Next the space between the deck and the insulation should have at least 4 inches of clearance. If not, you can place styrofoam channels between the insulation and the deck to allow air to come up from the soffits into the attic.

In your climate area, I would not like to use power fans because they can create enough vacuum to pull warm air from the living space into the attic, eventually causing condensation.

Finally, you have to do the calculation to see if the amount of ventilation you have meets the 1:150 ratio in a 50/50 balance. If not, you will need to adjust the quantity of ventilation upwards.

Remember that as warm air exits out the upper vents, it creates a partial vacuum, which should be filled from the unobstructed air at the soffits. The goal is to have even flow across the whole roof (not just in some sections). Side vents will allow easier air entry than soffits, and having them together with ridge vents will result in only the top of your roof being ventilated.
 
  #5  
Old 01-26-06, 10:11 AM
sitedrifter
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I just checked and I do see some light coing from the soffit area. Not light along the complete soffit area but in different spots. Tonight I am going to look again but use a BRIGHT flashlight shining into the soffit area. I think I will get a good look at how much of the soffit is allowing ventilation.

I am guessing that my home used the soffits in conjunction with the side vents.
I used a vent calculator and for my 16 sqaure roof, it says I need 384sq inches of venting. Or 31 feet of ridge vent at a 1:300 Ratio or 62 feet of ridge at 1:150 . My roof is 48 feet long so I guess the ridge is out but could 44 feet (2 feet short for first section of roof (1 ft on each side of vent) and 2 feet short for second section of roof) cut the mustard? I mean what I have now according to vent calculations is about 20 percent of what I would have.

I wish things were much easier or that there were contractors that really understand this stuff in my area.

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Old 01-26-06, 11:02 AM
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Venting...

44 ft. of ridge venting in your situation is better than the minimum, and providing you can ensure you have enough intake, you should be fine with the ridge vents and still block off the side vents.

Different brands of ridge vents have different effective ventilation areas so you may want to check around. Same goes for the soffits.

As for roofers knowing about ventilation - yes, the good ones who care about doing the right thing, do. Unfortunately, there are many who are, in my opinion, "shingle-bangers", and know as much about the other fine points of roofing such as flashing, waterproofing, and the roof as a system, as they do about ventilation. I've given advice on this board before about how to find a good roofer - it's not magic, it does require some work on the part of the homeowner, and you will have to pay for the expertise you get. There are good guys in your area, but they probably don't advertise as they are already as busy as they can handle, so talking to friends, neighbours, etc., and then following up the references is really important.

Good luck, and maybe, let us know how things turned out...
 
  #7  
Old 01-26-06, 12:47 PM
sitedrifter
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pgriz

Thank you for some quality information


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  #8  
Old 01-28-06, 08:54 AM
sitedrifter
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Checked and while I see very little light, it looks like the insulation is blocking most of the soffit vent area.

One roofer suggested not to rely on the soffite vents because they could be blocked and/or not done properly since it was not such an issue to worry about with home builders 30 years ago. His suggestion was ridge vent and vents at the eves on the back of the house. he said they will draw air in and go out the ridge vent. I aksed him would the circumvent the soffit vents. He said not really since most are covered with insualtion and since the eave vents are so low on the roof (1 to 2 feet from the edge) there would be no issue. He also said to close off the gable vents since the ridge will replace that.

That sounded good to me, does it sound good to anyone else here?

pgriz ??


I really want good ventialtion since I do see mold up there (bad in some spots because before I moved in, the bathroom vented into the attic)


Thanks


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  #9  
Old 01-28-06, 11:40 AM
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I'm no expert on attics and ventilation, but I would go with your 25% minority based on what I've read on the subject. This is how I understand it:

Soffit to ridge venting is the best form of ventilation. Hot air rises, thus it will move from low to high of its own volition. The soffit is the intake and the ridge vent is the exhaust. If a power vent is added to this scenario, the power vent will draw air from the area of least resistance. So if your power vent is located 3 ft from the ridge, you can bet that it's going to be drawing a large percentage of it's air from the ridge- not from the soffit or the rest of the attic. (I would call that a waste of electricity- venting fresh air from the ridge into the roof then back to the outside again.) The same could be said for the gable end vents, if the power vent is anywhere near the gable end. Gable end vents work best when there is a prevailing wind- one side becomes the intake, while the other is the exhaust. The cross-breeze provides the ventilation.

Gable vents would short-circuit the flow of air in a soffit to ridge vent situation. You'd be drawing less air from the soffits if you left the gable vents in place. "Properly constructed" and unblocked soffit vents will provide the best ventilation because they are usually distributed evenly around the perimeter of the home and will draw air from all locations. Continuous ridge venting is usually the best ventilation (except in hurricane areas where codes may prohibit it) since it allows air to exhaust from the peak, where the hottest air is located.

If insulation is blocking your soffit venting, the proper thing to do would be to install styrofoam proper vents in your rafter bays, then tuck fiberglass insulation underneath the proper vent. This doesn't require much skill and it's relatively easy to do. I'm sure you could do it yourself.

Adding continuous venting along the eve is also a possibility, using a product such as Smart Vent by DCIproducts, which is made for homes without soffit vents or homes that have inadequate soffit ventilation. Smart Vent can be installed under the initial row of shingles, and a 1" continuous vent is cut below it to allow intake ventilation.
 
  #10  
Old 01-28-06, 03:09 PM
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Ventilation

XSleeper, for someone who claims not to know much about ventilation, I think you are being 'way too humble. You're given a very clear exposition on the subject.

Site, if the soffits are covered with insulation then the insulation has to be removed. No ifs, ands, or buts about it. While it is not scintillating type of work, it is something that most homeowners can do (especially if they want to be sure that it is done right). Once the soffit cavity is clear, you have to ensure that the air gets into the attic by using the styrofoam channels (noted both by Xsleeper and me), and use these to keep the insulation from obstructing the air flow. These styrofoam channels look a bit like giant egg cartons, with a "W" shape, about 24 inches wide and usually about four feet long. They are easiest to install with the soffit off and you pushing them up between the insulation and the roof sheating, between the rafters.

I am definitely not a fan of eave vents. I've seen snow build up around them and then either cover them, or let melt water in. They also do not deal with the actual eave since they let air in a couple of feet above the actual edge, and the most vulnerable place on the roof is actually the eave itself. It is usually there that we find rot in the sheathing. Look, I could be wrong, but roofers that I respect never put them in, and roofers that go out of business every three years love them. I'm sure you can guess what I think of that suggestion.

The product that XSleeper refers to as "smart-vent" is better than the eave vents, but still not as good as properly functioning soffit vents. As he notes, sometimes you don't have a choice, but Site, in your case you do.

In case you're wondering, I'm a licensed, professional roofer with ten years of experience, operating under the same name the whole time, and most of my business comes from referrals. Since I am not in your area, I cannot help you directly, but at the same time, I absolutely get livid when I see roofer wannabees take the customer's money and give them shoddy service and installation.
 
  #11  
Old 01-29-06, 06:29 PM
sitedrifter
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I mean, what is the problem with these roofers. I have seen 6 already and they all have different stories and none of them seem to want to do the right thing. The roofer I saw today said:

1. I am a preferred owens Corning Contractor..

2. You want the gable vents along with your ridge vent. Owens Corning recommends it.

3. You do not need the soffit channels.. no need. we will just move the insulation a bit with a rake.

for # 3, I could see if the cut the insulation back 4 inches or so, otherwise it will just expand back to clog the soffit area.

I have 3 more roofers coming out. that will make 9. they have ranged from joe shoe to Master this, certified that, 30 years in the business. Well, that is all well said and good but if they do not know about good ventilation... That scares me

Reading posts on this board (Thank you) as well as researching my butte off on the internet, I think I have a good feel for ventilation now.

1. Ridge vent

2. remove and re sheathe gable vents

3. remove power attic fan

4. clear away insulation from soffit area

4. install soffit channels


Terrible thing is, the roofer yesterday dnt he one today, I asked for them to do this and they said, not needed or we will do it my way. I just don't get it!!!! I guess since it is really not alot of money to be charged for the sinple things, they tend to blow it off as being " not needed or overkill"

(if there is a roofer in NJ that knows what they are doing, send me a private message)

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  #12  
Old 01-29-06, 09:39 PM
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Thank you for the update

Site, thank you for the update. Frustrating, isn't it? I had a similar experience when I tried to hire some electricians and plumbers. I did my homework and had a very specific list of things that I wanted to see, such as a detailed written scope of work, payment terms, guarantee, request for proof of insurance and license, and a list of references. NOT ONE was able to give me what I would consider basic information. It's not like I'm dreaming this up, since this is what we give each of our own clients.

You're doing good. Now that you are an educated consumer, don't let down your guard. The bad news is that many roofers are just as clueless about basic roofing as well. I know this from the amount of repair work we get. Make a list of exactly what you want done and make sure your roofer delivers. If you have some of your facts wrong, a good roofer will be able to explain why, in detail. Good luck.
 
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Old 01-29-06, 10:29 PM
sitedrifter
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I will be sure to post how I make out!


Thanks again for all the information!

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  #14  
Old 01-30-06, 04:25 PM
sitedrifter
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Well

At least I found a contractor that will do what I want even though he thinks it is wrong/overkill. He even went on to tell me that a GAF rep was on one of their jobsites (very very large job) and the rep required them to leave the gable vents in addition to adding the ridge vent.

I can tell you this contractor thinks I must crazy or at least a pain in the arse but it is my home, not his and I want it a certain way.

I emailed him and told him a few more adjustments to the quote and we should be all set, that is unless he tells me to go fly a kite

What an ordeal for what seems to be such an easy thing. But hey, I guess for eveyone of me, there are thousands of home owners that don't care or beleive anything told to them which these types of contractors love.

At least these guys are listed as Master Elite with GAF and only 1 complaint in 3+ years which was resolved.

Will post on my choice of contractor when made as well as how it turns out..

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Old 02-25-06, 09:22 PM
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This has been a very informative thread for me. I need to do the same exact thing. I have one question. Does the styrofoam have to be intalled from the outside of the house, or can you get up in the attic and install it from above?

Thanks,
Josh
 
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Old 02-26-06, 05:22 AM
sitedrifter
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From what I see, I think it would be easier to install from inside the attic. that is what I am going to do


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Old 02-26-06, 05:30 AM
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Installing Styrofoam channels

It can be done either way. However, if the slope of the roof is relatively shallow (say, 5:12 or less), then it can be difficult to get access to the areas near the eaves from the attic. So in those situations, working from the outside is easier. It also depends on the roof configuration. Simple ranch style layouts generally permit easy access to all sections of the roof, while some of the designs with multiple dormers and different sections can be extremely challenging to get to from the inside.
 
  #18  
Old 02-26-06, 11:29 AM
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I have a ranch with a shallow roof as you say. While it is possible to get access to the soffits from the attic, it is a tight squeez! I just put recessed lights in, so I was up in the attic for three days straight.

Anyway, I'm not familiar with the construction of soffits. Do you just have to pull off of the vinyl soffit piece that has the vents in them, then you have acess to cut the insulation back and push the styrofoam thing up there?
 
  #19  
Old 02-26-06, 05:31 PM
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Soffit Construction

The soffits are usually just sitting inside two opposing channels (one along the house and one along the edge of the eave), with the seams oriented from house to eave. There is usually at least one nail holding each soffit piece, and if you pull that out, you should be able to pop the soffit out, or at least move it laterally. Once you're done, you move the soffit piece back. Try it with a couple of pieces in a low-visibility area, and one you get the hang of it, it'll go very quickly.
 
  #20  
Old 02-26-06, 07:06 PM
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Insulation!

Sitedrifter --

This is a real interesting thread for me, too, since I've been wondering about the venting that was done on my re-roof 4 years ago.

My house is a cape, up here in western Ny state and my upper floor ( a large bedroom and hallway) has been freezing ever since the re-roof! It was always cold before, but I suspect that the installation of the soffit vents and ridge vents has made matters worse. If the temp on the first floor is 65 degrees, it's at least 10 degrees less upstairs.

The thing I want to bring up is: Don't overlook the insulation angle. I have a decent amount on my attic floor but i suspect that what's in the knee walls could stand some upgrading, not to mention what's in the roof area above the upper bedroom. Better make sure that what you have is in good shape, and perhaps plan on budgeting something for adding some more. Just my opinion...I'm not an expert, just someone learning from experience. Good luck.
 
 

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