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capecod in NJ: cathedral ceiling unvented roof open cell? or closed cell? foam


mxl4729's Avatar
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10-17-07, 08:27 PM   #1  
capecod in NJ: cathedral ceiling unvented roof open cell? or closed cell? foam

I am looking for people who have used spray foam in an attic or cathedral ceiling to create an unvented roof.

did they use open cell or closed cell foam?

Did it work reducing the heat?

any moisture problems?


My story is I live in NJ and have a capcod or 1 1/2 story house. So the roof is my ceiling upstairs.
the rafters are only 5.5 inches deep.
I have no soffets for air intake.
I have a ridge vent which is worthless because i have no air intake. So as of now I have an unvented roof

i have gutted the area and need to insulate. it gets ungodly hot up there and was hoping to fix this.

i have gotten quotes for spray foam for open and closed cell. both are $3000 for my area of about 1000 sq ft.

3 inch of closed cell or 5 inches of open cell.

All the people that sell open cell say to go with open cell all the people that sell closed cell say to go with closed cell.

i want to know if anyone here has used ether and if they have had problems. i am not sure what my other options are but from what i read on these forums it would be to add venting which I do not really see how I can do because I have no soffets. This is why I would like to go with an unvented setup.

some large pics to show what is going on

my house see no soffets


were the rafters of the second floor meet the walls
you can see that it gets so hot up there that it has cooked some of the resin out of the wood rafters



full view of the walls



you can see the discoloration of the underside of the roof decking



under side of my useless ridge vent





thanks matt

 
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resercon's Avatar
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10-19-07, 08:27 AM   #2  
This shows an example of how to provide attic ventilation to the lower portion of the roof.

http://www.toolbase.org/TechInventor...&CategoryID=10


This site on page 4 shows the different ways to insulation and ventilate the area behind the knee wall.

http://www.eere.energy.gov/buildings...pdfs/26447.pdf


Without getting to technical here the primary purpose of attic ventilation is to bypass the low water vapor permeability of roofing materials. The water vapor molecule is so small that it will permeate all known building materials. Example, all building materials have "Perm Ratings" This is an indication of the time it takes for water vapor to permeate the material. The lower the Perm Rating the longer it takes for moisture to permeate it. Vapor barriers and roofing materials have a much lower Perm Rating than any type of foam, closed cell or open cell.

For this reason I would not recommend foam for your application.

 
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10-19-07, 05:20 PM   #3  
Dense packed cellulose would cost less but give slightly less R value. It would block ventilation just like the foam but be more forgiving when a small amount of moisture came into contact. It is being accepted more and more when the decision to eliminate ventilation is made. As far as I know, Elk is the only shingle manufacturer that doesn't get upset and void warranties when there is no ventilation.

Ken

 
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10-19-07, 05:39 PM   #4  
I took a look at he links and the Drip Edge System it looks like what I need but from what I read it must be installed before the shingles. I do not have that option to remove the roof it is brand new. So I am not sure the drip edge system will work for me.



Any other options for not venting systems? Has anyone here have an unvented roof in or around NJ for a few years with no problem?

How is this Dense packed cellulose installed after or before the sheet rock. And does it relay not need ventilation? Does cellulose not absorb water?

 
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10-19-07, 05:56 PM   #5  
That looks liek a good product. But like you said, it goes on before the shingles and iceshield. Cellulose absorbs water but where is the water going to come from? When installed to a density of 3.5 lbs/cu. ft. It has an R value of about 3.1/inch and never settles. We install before or after drywall depending on whether there is any access to knee attic after drywall. Before the drywall requires fabric or poly stapling. Check out www.parpac.com I think they even show unvented cathedral ceiling installation there. I can say it works for saving energy, but I haven't observed it long enough to verify the absence of roof damage. I would do it in my house without thinking twice and I don't even have a cape cod. Those things are like miniature human ovens in the summer.

Ken

 
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10-19-07, 06:21 PM   #6  
Posted By: KField Cellulose absorbs water but where is the water going to come from?
Ken

some water all ways finds its way in from what i read. what happens if cellulose gets water in it? will it grow mold?

my capecod is a people cooker. That is the reason i need to increase the insulation. but i want to do it in the correct way. i have no problem spending $3000 or so but i want to make sure i do it right. no mold and for it to stay cool up there.

 
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10-19-07, 06:35 PM   #7  
I'm not convinced that water always gets in but it does have a way of showing up in the worst places. Cellulose will wick water away and diffuse the wet spot but anything that gets over 55% humidity or moisture content will support mold growth at the correct temperature. I would not be too concerned about the roof area. If the roof went bad, you may have to replace the cellulose too but the same would be true of fiberglass and the the insulation value of fiberglass leaves a lot to be desired.

Do you spray yourself with Pam at night so you don't stick to the bed? Just kidding.

Ken

 
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