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Old 06-28-2012, 05:17 PM   #1
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enough ventilation?


Getting new roof. Want to get attic ventilation right if possible.
Have soffit venting on most of the back of the house and the attached garage. A gable vent on each (2) sides. Its the front that has me concerned. There is a bay window that has no overhang above it and is a area that gets ice dams.The right front of house is a large dormer(?) that is not vented.The front porch area does have soffit vents on two sides.

Is this enough?

One roofer told me they always install ridge vent and don't seal off gables. That is wrong from what I have read. (He also offered to bill my insurance co. more than he would bill me to recover my deductible. Isn't that called fraud? )

The other roofers seemed disinterested in investigating my attic ventilation, although they all offered to install ridge vent if I wanted.

I have attached pics.
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enough ventilation?-frt.jpg   enough ventilation?-back.jpg   enough ventilation?-side.jpg   enough ventilation?-bay.jpg   enough ventilation?-frt-r.jpg  

enough ventilation?-sof.jpg  

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Old 06-28-2012, 06:26 PM   #2
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enough ventilation?


im a roofing contractor and ive never seen soffit venting on just one side of the house, thought is was suppose to bring the air in and across the backside of the plywood to keep moister off it. as for ridge vent, well we install a bit of here in arizona to get the heat out. there a formula to figure out how much intake to how much out. has for teh roofer billing the insurance company, might be the faxct that you really needed from the beginning and therefore its missing. and looking at how many sections of roof you have i say you really need it. sounds like he was the only one that did show any kind of interest in doing it right. guess you could tell him not to bother with the insurance company and youd like to pay for it out of pocket. they do have to cut back on each side of all the ridge areas.

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Old 06-29-2012, 12:47 AM   #3
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enough ventilation?


More venting will help deter ice dams: http://www.extension.umn.edu/distrib...ng/dk1068.html
The lack of a soffit over the bay windows require foamboard above them in the attic, air sealing the whole attic first;https://docs.google.com/viewer?a=v&q...bBVYCRHz6fk5Ng

The 1' deep soffits in front are only 4.78sq.in. per ft.- a good ridge vent (18 NFVA) requires 9"- or continuous soffit venting: SV 202; http://www.airvent.com/homeowner/pro...it-specs.shtml

Read below in that link to figure required venting... The little gable end vents they supply today are a joke- scroll back and read from "Ventilation" chapter: http://books.google.com/books?id=Z8a...0vents&f=false

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Last edited by Gary in WA; 07-01-2012 at 06:16 PM. Reason: corrected NFVA per manu.
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Old 06-29-2012, 07:22 PM   #4
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enough ventilation?


This home was built 2004 and was not cheap. I bought it in 2009 and hired a respected home inspector before closing. He put in his report attic ventilation was adequate. I guess neither the builder ( one of the largest in Midwest) nor the inspector thought ventilation was important.
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Old 06-29-2012, 07:53 PM   #5
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enough ventilation?


yeah well if you watch any of the holmes on holmes youll see where big know builders, and a lot of inspectors, could give a damn if its built right or not. builders care about one thing, how much money, and inspectors have to let a lot of things pass or they wont get called out. here in arizona we dont have to worry about condensation on the underside of the roof but we do have to worry about heat, therefore the right amount of ventilation is important. as i said = i beleive the air has to travel up all around to flow across the underside of the roof sheathing. cant see where the air just traveling up one side is going to help any other section. guess the inspectors magic word was = adequate. anyway there are plenty of websites that tell you how to calculate the right amount of venting you need. and getting back to big builders, most, not all, but most of the bigger builders are the worse. you can tell whats going on with a builder when you go on a job site and just look at how the sub-contractors are working, do they emm in a bad mood or are they in a good mood. bad mood = there not making any money, dont make money = do the minimum.

Last edited by hotrod351; 06-29-2012 at 07:56 PM.
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Old 06-29-2012, 11:13 PM   #6
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enough ventilation?


What bugs me is that all of the labor in this area is highly paid union guys who know better. I have found plenty mistakes from all the trades. I know the builders push these guys but a little short cut can lasts for decades.
Who would you hire to come out and fix a poorly vented attic?
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Old 06-29-2012, 11:21 PM   #7
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enough ventilation?


I thought I posted about this last night and it was deleted or something. I was very negative and advised just selling the house.

I would hate to have to deal with such a mess.

But I did think of one thing you could do, and it doesn't involve suicide.

I have heard on this very forum about below shingle intake vents. I've never seen them, but I imagine that you can take off a few rows of shingles down way low on the roof, cut the sheathing, and install this product and then shingle back over. I don't know how well these things work, but that is the only option I see for you.
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Old 06-29-2012, 11:45 PM   #8
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enough ventilation?


I have seen those vents. Pretty weird looking on front of house. I had a roofer look at it today.He measured and said there was enough total vents to pass code but there were areas unvented. He did not think a ridge vent was the answer. He also said that any roofer who always installed ridge vent without doing the calculations didn't know much about venting.

Hey, this house is way better vented than my last house. That one had two gable vents and nothing else!
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Old 07-01-2012, 06:37 PM   #9
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enough ventilation?


I corrected my calculation on your soffit venting to 4.78NFVA, still 1/2 as much as you need, if they are 12" deep of open soffit, not counting the end J-moldings holding it up there. I'd get more estimates if that roofer thinks you have enough soffit venting with every third one perforated. With a short soffit depth as I see, you should have every panel vented to equal/exceed 9" per lineal foot of soffit.....http://bluelinxco.com/Portals/0/docs...20Brochure.pdf

If the gable end vent pictured is 12 x 18 = 52 sq.inches NFVA added to one at the other end, equals 104" sq.in. of total exhaust--- enough for 225 sq.ft. attic.Your house appears larger than that, I hope you have other exhaust vents...

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Old 07-02-2012, 11:09 AM   #10
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enough ventilation?


The attic floor including garage is 3000 sf. I have vaulted ceilings in half of the house but the space between the top of the vaulted area and the bottom of the roof is still 3 or 4 feet. The gable vents are 24X30. Still not enough, I know. There is a 5'X5' unvented ceiling under the front porch that is open to the house attic. This would be really easy to replace with continuous soffit. I will attach a picture. Would this help at all? I am hesitant to have ridge vents installed without enough lower inlet air flow. Also, I can't be sure the rest of the soffit vents are clear of insulation until it gets cool enough to go into the attic. Thanks for your information.
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Old 07-04-2012, 11:40 PM   #11
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enough ventilation?


Where are you located, Mike?

The ice dams are from lack of ventilation and insulation. First air seal the attic, then bring insulation up to minimum code. Certain circumstances are better off without passive attic ventilation. You need it to deter the ice forming. Rigid foam board over the shallow exterior walls (rafter/joist area) will help stop the heat loss there, melting the snow. Have the roofer at least install a layer of Ice&Water shield at the overhangs; http://www.buildingscience.com/docum...d-135-ice-dams

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Old 07-05-2012, 02:09 AM   #12
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enough ventilation?


I believe GBR is right in that the lack of insulation is causing the ice dams. Heated air is leaking from your house into the attic. (non-contact can lights can help cause them, are yours non-contact?) In this process you should make sure your insulation adequate and the ceiling is sealed as best as possible.

Then do the math yourself on the ventilation. Don't trust anyone to do it for you. Fire the roofers that don't understand ventilation. Every area of the attic needs to be ventilated for your type of construction.

First look at your intake. You must have more intake then exhaust. The new 2012 IRC is actually calling this out. I didn't check anything like GBR did but you probably need to take out the soffit panels, make sure you have a continuous opening in the attic and up to the ridge. (No insulation blocking the air, but also make sure your insulation extends all the way over the top plate.)Then install continuous vented soffit panels. The 5x5 area won't help. You want an even, balanced intake at the eaves, not one big open area.

Then look at your exhaust - don't mix the types. Gable end vents are not going to work, so seal them or get rid of them. Options now are ridge vents, static, and power. Looking at your house I would think ridge vent is the way to go. Just do the math for the type of ridge vent you are installing and make sure you have less NFA then the intake.

The idea is you want to keep a positive pressure in the attic so heated air is leaking from your house into the attic. Make sure you check out the can lights well and make sure they are sealed. You can seal them another way if they are non insulation contact type. Don't push insulation up on them.

For the areas with no soffit ventilation you can add ventilation under the shingles and probably not notice it. There are products like smartvent by dci, and GAF has a new fascia vent. I don't mean to endorse or promote any products, just let you know there are options.
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Old 07-05-2012, 10:08 AM   #13
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enough ventilation?


First I would like to thank everyone for taking the time to help me with this. GBR I live in St Louis Missouri area, cold winter and hot summers. Roofnron, I did the math. There is 3000 sq ft attic floor including garage. I have about 545 nfa in the soffits. There should be 720 nfa. The 2 gables come to about 194 nfa. Way short of the 720 needed. One more question. One of the gable vents will be just about impossible to seal from the inside due to the vaulted ceiling protruding into the attic that is covered with deep blown in insulation. There is no way to crawl over that because the vault is pretty close to roof bottom. Can these vents be sealed from the outside somehow?? Thanks again for your trouble. Mike
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Old 07-05-2012, 04:12 PM   #14
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enough ventilation?


It would be very easy to pull the vent from the outside and seal it up. If you can get matching siding you can leave it out, or just seal up the opening in the wall and put it back for looks.

I would look at the 720 nfa as minimum, 2012 IRC doubles the requirement for your climate zone. Try to attain 720 to 1440 evenly distributed for intake. Good Luck on your work. Sorry you are having to mess with a re-roof when the roof is not so old.
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Old 07-06-2012, 12:10 PM   #15
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enough ventilation?


With all those can lights, you are going to always have premature snow melt and issues.

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