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Question About Venting Roof?

 
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Old 03-30-2014, 12:06 PM   #1
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Question About Venting Roof?


I have a basic hip roof 4/12 pitch that currently has ridge vent and soffit vents. The house is half vaulted ceilings and the vaulted part does not breathe. Major ice heaves in winter

I will be adding 3" of ISO Rigid foam over decking, then grace ice and water sheild membrane over ISO. The I will be adding 1x4 batten system perpendicular to the eaves every 9" oc to allow the new steel roof to vent under the steel.

I also will be adding a cora vent at the eave for my intake and a new fascia over that.

The ridge will also be vented.

Since the new roof will be vented is there any benefit to leave the soffit vented or is it best to use solid soffit and close it off?
I will be doing all new soffit and fascia on house along with roof. I planned on closing them off.

Experts Opinion on the venting only please?

The picture is not to scale, just something i drew up for a better idea.
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Question about venting roof?-iken-roof-plan.jpg  

Last edited by stombaugh85; 03-30-2014 at 12:11 PM.
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Old 03-30-2014, 02:30 PM   #2
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Re: Question About Venting Roof?


From what you described, you are doing a hot roof. Are you just working on the outside of the house? Are you asking about just venting the sofit area itself? I wouldn't bother if that is your question. But you need to make sure that the old vent pathway is completely air sealed, or they will continue to have problems. And your 3" of polyiso will be useless. Can you list the materials in the roof from the inside out? That would be helpful on giving you advice. Also, what climate zone are you in? Nick

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Old 03-30-2014, 04:21 PM   #3
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Re: Question About Venting Roof?


Check these guys out......http://www.buildingscience.com/


Click on book store,five book choices will pop up,choose the one appropriate for your climate zone. I think you will find your answer easily there.



Good luck
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Old 03-30-2014, 08:45 PM   #4
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Re: Question About Venting Roof?


Quote:
Originally Posted by Morning Wood View Post
From what you described, you are doing a hot roof. Are you just working on the outside of the house? Are you asking about just venting the sofit area itself? I wouldn't bother if that is your question. But you need to make sure that the old vent pathway is completely air sealed, or they will continue to have problems. And your 3" of polyiso will be useless. Can you list the materials in the roof from the inside out? That would be helpful on giving you advice. Also, what climate zone are you in? Nick
My question is what to do with the original soffit vents. My plans were to seal them off and use solid soffit along the eaves since the roof itself will breathe. Just want to confirm my thinking was correct
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Old 03-30-2014, 08:52 PM   #5
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Re: Question About Venting Roof?


Quote:
Originally Posted by Morning Wood View Post
Can you list the materials in the roof from the inside out? That would be helpful on giving you advice. Also, what climate zone are you in? Nick
On the vaulted ceiling section from inside/out it goes like this
t&g 3/4 wood
1 1/2 rigid foam
deck ( 1/2 plywood
then my 3" iso
layer of grace ice and water guard
1x4 battens
steel roof panel


Rest of the house is regular ceiling and attic space with r 30 insulation
Climate zone 5
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Old 03-30-2014, 08:59 PM   #6
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Re: Question About Venting Roof?


Quote:
Originally Posted by stombaugh85 View Post
On the vaulted ceiling section from inside/out it goes like this
t&g 3/4 wood
1 1/2 rigid foam
deck ( 1/2 plywood
then my 3" iso
layer of grace ice and water guard
1x4 battens
steel roof panel


Rest of the house is regular ceiling and attic space with r 30 insulation
Climate zone 5
What is in the rafter space, and what is the depth of the rafters? Also, what is the 1 1/2" rigid foam? poly iso, xps, eps?
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Old 03-30-2014, 09:27 PM   #7
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Re: Question About Venting Roof?


Quote:
Originally Posted by stombaugh85 View Post
On the vaulted ceiling section from inside/out it goes like this
t&g 3/4 wood
1 1/2 rigid foam
deck ( 1/2 plywood
then my 3" iso
layer of grace ice and water guard
1x4 battens
steel roof panel


Rest of the house is regular ceiling and attic space with r 30 insulation
Climate zone 5
It's Double sealed, which is no good. Rot city. If you were to apply a supersealed 6 mil V/B to the inside of the envelope which would guarantee a minimal exchange (leakage) rate then whatever you do on top of it is irrelevant. In this case? You're setting yourself up for heartache down the road. Never rely on these products when you are considering the integrity of your envelope. EVER.
They are subject to "installer errors" (seldom corrected). This is a constant up here.
As Hugh Dillon sang? "I smile and wave"...
I'm in Edmonton. We do Insulation here. It's kind of important to us...
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Old 03-30-2014, 09:27 PM   #8
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Re: Question About Venting Roof?


Quote:
Originally Posted by Morning Wood View Post
What is in the rafter space, and what is the depth of the rafters? Also, what is the 1 1/2" rigid foam? poly iso, xps, eps?
the 1 1/2 is existing ,put in 10 years ago at least, not sure,

The rafters are 2' OC 2x6
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Old 03-30-2014, 10:01 PM   #9
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Re: Question About Venting Roof?


Quote:
Originally Posted by Terrorron View Post
It's Double sealed, which is no good. Rot city. If you were to apply a supersealed 6 mil V/B to the inside of the envelope which would guarantee a minimal exchange (leakage) rate then whatever you do on top of it is irrelevant. In this case? You're setting yourself up for heartache down the road. Never rely on these products when you are considering the integrity of your envelope. EVER.
They are subject to "installer errors" (seldom corrected). This is a constant up here.
As Hugh Dillon sang? "I smile and wave"...
I'm in Edmonton. We do Insulation here. It's kind of important to us...
Thermal Bridging will be at a bare min or non existent at all with the steel roof being vented on its own. If anything the extra 3" of ISO will create a somewhat of a conditioned roof below.

What is there to rot?

Are you suggesting a breathable material like felt would be a better option instead of ice and water shield over ISO?

The existing roof is shingled with the 1 1/2 foam board and t&G already in place. Its been in place for over 10+ years and no signs of rot anywhere. The deck is solid with no stains or evidence of moisture issues.

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Old 03-30-2014, 10:08 PM   #10
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Re: Question About Venting Roof?


Quote:
Originally Posted by stombaugh85
the 1 1/2 is existing ,put in 10 years ago at least, not sure, The rafters are 2' OC 2x6
So the 2x6 space has what in it? Nothing? I also don't like the foam board on both sides of the roof. It's better on the outside. Say you seal the exterior really well. Any water vapor(moisture) inside the house can still get into the roof assembly and migrate up to the polyiso. That isn't good if the dew point is in the rafter space. You will,get rot at that point. I think I'd strip the sheathing and insulate the rafter bay with closed cell foam. Then reapply the sheathing and air seal it really well. Then add your polyiso if you want to, strap it with 2x's and not 1x's too.
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Old 03-30-2014, 10:17 PM   #11
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Re: Question About Venting Roof?


Quote:
Originally Posted by Morning Wood View Post
So the 2x6 space has what in it? Nothing? I also don't like the foam board on both sides of the roof. It's better on the outside. Say you seal the exterior really well. Any water vapor(moisture) inside the house can still get into the roof assembly and migrate up to the polyiso. That isn't good if the dew point is in the rafter space. You will,get rot at that point. I think I'd strip the sheathing and insulate the rafter bay with closed cell foam. Then reapply the sheathing and air seal it really well. Then add your polyiso if you want to, strap it with 2x's and not 1x's too.


The 2x6 space has unfaced fiberglass insulation .

Here is another picture of what I got going on except 1 1/2 board before the ceiling covering and batten system instead of decking. Link below

http://www.buildingscience.com/docum...es-and-manuals

Scroll to the bottom picture.

Last edited by stombaugh85; 03-30-2014 at 10:21 PM.
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Old 03-31-2014, 06:28 AM   #12
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Re: Question About Venting Roof?


You can go with two layers of foam BUT you had better have all your details perfect - no water in, no issues - water gets in and the fun begins. Maybe I missed it but where are you located or at least which climate zone - that will determine how much foam you do need at minimum
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Old 03-31-2014, 11:18 AM   #13
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Re: Question About Venting Roof?


Quote:
Originally Posted by SLSTech
You can go with two layers of foam BUT you had better have all your details perfect - no water in, no issues - water gets in and the fun begins. Maybe I missed it but where are you located or at least which climate zone - that will determine how much foam you do need at minimum
He's climate zone 5.

I don't see how two layers of foam is a big deal. I have hot roof with closed cell flash on underside of sheathing and then EPS on underside of rafters for a thermal break. That seems scarier than this proposed detail.

I think you definitely need to make sure the dew point is not in the fiberglass. If it is and you can't put enough foam on the exterior to prevent that, then yank the fiberglass and put closed cell in the rafter bay.
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Old 04-02-2014, 12:38 AM   #14
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Re: Question About Venting Roof?


You left out a few details on your drawing. I assume there's drywall under the rafters, so you're leaving hollow rafter bays? Or is there more insulation in there? Where are you located and how much snowfall do you get? Whatever your design, ice dams and condensation inside your roof are the two things you want to avoid.

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