R-36 between 2X12s

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  #1  
Old 02-01-02, 12:14 PM
toucansam
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R-36 between 2X12s

I am in the process of insulating the cathedral ceiling in new construction by placing R-36 batts between 2X12s on 24" centers. The batts will completely fill the space, so I am using a styrofoam dura-vent product to insure that I get proper ventilation between the eaves and the cap vent. My question is, how much R value will I lose by slightly compressing the batts? Since the roof is has a 12X12 pitch, the verticle depth of the insulation will be nearly 17 inches. Should I add 2"X2" spacers on the 2X12s to allow the insulation to expand to it's proper dimension?
PS Local code calls for R-19 in walls and R-36 in ceiling.
 
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  #2  
Old 02-01-02, 04:15 PM
rbisys
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Greetings,

Using fiberglass insulation in a cathedral ceiling will cause you to have a very, very warm room in the summer.

The glass absorbs over 90% of the heat energy from the sheathing (radiated) and this heat will help warm up the rafters which will conduct to the drywall and then into the room.

Since the batt is about 98% airspace it also allows for a great deal of heat energy to radiate thru. Your ceiling becomes a giant heat radiator. Over 90% of the summer heat gain in a ceiling is radiant heat.

The way I insulate these ceilings is to use two layers of radiant barrier insulation(RBI). One layer between the rafters and the second on the bottom like a vapor barrier. I then install 7/8" steel fuuring strips across the bottom of the rafters and then the drywall. The RBI is also a superior vapor barrier and you will have no condensation problems.

The RBI reflects about 97% of the heat energy both ways and the furring strip isolates the rafter from the dry wall minimizing the conducted heat energy.

Thank you for considering my opinion.
 
  #3  
Old 02-01-02, 04:29 PM
toucansam
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I understand your RBI theory, but I have to meet an R-36 requirement. I don't think that the 2 layers of RBI that you propose will meet the code requirements, unless I sandwich another insulation in between. Summer heat in northern Michigan is a lot less of a problem than winter cold.
 
  #4  
Old 02-01-02, 04:48 PM
rbisys
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Greetings,

Unfortunately you are another victim, among millions, that are forced to use substandard materials to insulate your home. You can thank the bed partners, US Senate and fiber glass industry for that. The RBI system would out perform, for winter, the "R" 36 for your area although I would recommend a 3 layer material.

As you probably know the fiberglass industry cannot provide installed winter condition tests that validates their phony "R" factors.

Thank you for considering my opinion.
 
  #5  
Old 02-01-02, 04:49 PM
Insulman
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I would like to see you try to get an inspector to approve 2 layers of radiant barrier, thats almost funny!!

I assume you actually are considering R-38 batts which are 12" thick. Being that your 2 x 12's are actually only 11 1/2 inches deep, you will be compressing probably 2" of insulation after installing the batt. this will not only lose r value but in addition put addition stress on the drywall after installed.. I would Either Install R-30 batt, probably thats all you'll end up with after compressing a 12" batt. Or the other option is to purchase high density fiberglass batt which is R-38 but only 10 1/2 inches thick.. It is a bit priceir than the standard R-38 batt however realise this once you drywall you cant change the insualtion without going to great expense.

If you can't locate it in your area l might be able to direct you to an outlet that can supply you with the R-38 high density batt..

Good Luck

Jim
 
  #6  
Old 02-01-02, 05:54 PM
rbisys
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Greetings Insulman,

No it isn't almost funny, it's sad.
It's sad because you are a fiberglass salesman that promotes a product that is a proven carcenogenic with both fibers and chemicals. You also know that people can become chemical sensitive to these chemicals and lead a miserable life. You know that mold grows on your product and can that certain molds can cause serious illness in children and older adults.

You also know that the products you push lose up to 50% of the advertised "R" factors that are printed on the label. You also know that you cannot provide any independent tests showing that fiberglass gets its advertised "R" factors in the installed dwinter summer conditions.

You also know that the fiberglass industry can only stay in business by influencing state and government agencies.

You know this and still you try to harm people by pushing your posion. What kind of person would do this? What areyour motives for wanting to harm people? I think every one reading this would like to know.

Each time you choose to be arrogant and ridicule me and what I stand for I will write is same question.

Thank you for considering my opinon.
 
  #7  
Old 02-01-02, 06:00 PM
Insulman
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Actually I don't need to make personal insults against you, your own posts do that for me :-)))

Have a nice day !!
 
  #8  
Old 02-01-02, 06:16 PM
toucansam
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Gentlemen;
I don't know who sells what and don't want to promote a dispute. I am forced to meet code and that is what I am trying to do. An interesting side note is that in order to meet the R19 requirement for the sidewalls, the builder had to either frame with 2X6s to allow room for the required fiberglass or frame with 2X4s and use 1" R7 foam under the siding (R13 to be added between studs). A completely independent heating contractor told me that the R7 foam would do more for me than the R13 glass. His simple explanation was: "Have you ever held boiling water in a 1/8th inch foam cup? Multiply that by eight."
 
  #9  
Old 02-02-02, 07:11 AM
R
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New construction can be very frustrating and my opinion really doesn't count. The opinion that does count is your building inspector. Most building inspectors will be more than happy to advise you on building code prior to construction, it makes their job a lot easier. If you explain your problem to them and propose a solution, they will be more than happy to tell you if it meets building code. Just make it sound like you don't want to waste their time coming out to inspect.

The high density insulation is probably the least expensive way to go. Insulman is apparently a very experience, but I can not say the same about your local building inspectors because I don't know them. You should check with them before purchasing the product and installing it. You should also be prepared to present alternatives if your primary proposal doesn't meet their approval. DO NOT GIVE THEM MORE THAN ONE PROPOSAL AT A TIME.

You should also consider other aspects the inspector going to look for. The spacing of the nails or screws to attach the sheet rock, especially since your rafters are 24" on center. This is something you should ask the inspector when your making the proposal. If by chance the high density does not meet with their approval and they express concern about the rafter separation, there is an alternative.

Install the styrofoam baffles, then 10.5" batt insulation, then 1" rigid board insulation, then 1x2 furring strips perpendicular to rafters 16" on center. This should meet with their approval, but so should the high density, but just in case.

The insulation behind siding will not qualify as part of the wall inspection. If the insulation was put on the inside as it is mentioned above, it would. The reason for this is that vynal loses heat 2,000 time faster than wood and it's primary purpose with siding is to prohibit condensation.
 
  #10  
Old 02-02-02, 07:27 AM
toucansam
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Originally posted by resercon

The insulation behind siding will not qualify as part of the wall inspection. If the insulation was put on the inside as it is mentioned above, it would. The reason for this is that vynal loses heat 2,000 time faster than wood and it's primary purpose with siding is to prohibit condensation.
That is interesting, but the siding isn't vynal. The exterior siding is wood. I would think that the type of siding wouldn't be a factor. It could be metal, that doesn't change the R19 requirement. Wether it is constructed with the foam toward the outside or inside, I believe that the total R value is what the inspector will look at.
 
  #11  
Old 02-02-02, 07:51 AM
R
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You should check with your local building inspector, but I'm almost certain that siding is excluded for wall insulation. Though the siding mat provide insulation value to your home, the requirement pertains to the amount and type of insulation in the wall.
 
  #12  
Old 02-02-02, 08:07 AM
rbisys
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Greetings Insulman,

We're still waiting for your answer.

Where are the tests?
Why do you promote a dangerous and potentially fatal product?
Why do you promote a product that can't meet the advertised "R" values?

What kind of person are you that would promote such a product?

Why are you avoiding answering these important questions?

Like I said, these questions are not going to go away.

Inquiring minds want to know.

Thank you for considering my opinion.
 
  #13  
Old 02-02-02, 08:22 AM
rbisys
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Greetings,

The fact that the inspectors will not accept foam on the out side of the house proves how dumb they really are.

It doesn't make any difference how efficient the siding is or isn't, because the foam is still only about 20% efficient. The problem with putting the foam on the out side is that you can create condensation between the foam and sheating, or, between foam and siding. If on the out side it might help reduce the condensation inside the wall cavity. You will still have condensation. It takes about 1,100 BTUs / # of water to convert vapor to liquid. A house with fiber glass converts alot of vapor.

I know this will not help your immediate problem, but, I hope the knowlege is worth knowing.

By the way, you didn't start anything. This kid has been mouthing off for several weeks now and it's time he be brought up sharply.

Thank you for considering my opinion.
 
  #14  
Old 02-02-02, 09:47 AM
toucansam
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Guess I'll have to ask the inspector if that R7 foam counts as insulation or no. It's actually dumb to put it there if it isn't. The 2" foam outside the poured basement walls counts as insulation. That's another one of those weird code requirements. Howcome basement walls need to be insulated but basement floors aren't? Once you get a couple of feet down the earth is a pretty consistant 56 degrees. (only 11 or 12 degrees from normal room temp)
 
  #15  
Old 02-02-02, 10:10 AM
rbisys
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Greetings,

Actually you have to go down further.

The problem is that heat energy flows from hot to cold and the the greater the temp difference the greater the flow. So you stand to lose more energy thru the wall than the floor. You have a wicking process here.

Even though the flow thru the floor isn't as great, it is constant. I recommend to my customers that they insulate both.

Actually they did you a favor. You will save more energy doing this than installing the phony. unneeded "R" factors upstairs.

Thank you for considering my opinion.
 
  #16  
Old 02-03-02, 12:30 AM
Insulman
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Rbisys,

Why do you bad mouth me? All I do is offer people advice on what I have learned over the years from experience in the insulation business. But the funny part is, Is yes I sell fiberglass,
almost 6 million dollars in 2001.

I will gladly offer advice which I believe will help people do it themselves...effectively and less costly...

Now as to whether or not I should feel guilty about selling fiberglass because it is dangerous , Its because I dont believe it is... You have posted here numerous times about how fiberglass causes cancer... common sense says if you inhale an inordinate amount of any fibers fiberglass, steel etc.. it will be detrimental to your health.. So if you follow saftey ( ie breathing masks ) precautions the product is not considered to be harmful to humans.

Furthermore in October of 2001 the International Agency for Research (IARC), part of The World Health Organization convened a scientific working group of the worlds leading experts on the health and safety of man-made fibers, including glass fibers to re-evaluate these fibers as to their potential carcinogenic hazard.

Following a thourough review of all the medical-scientific data available. Much to your disliking I am sure rbisys, here is the outcome of that scientific panel.. The panel lowered the classification for glass wool fibers from a Group 2b classification ("Possibly Carcenogentic to Humans") to a Group 3 classification (*not classifiable as to carcinogenicity to humans*)

So perhaps you should quit posting outdated facts..

I do honestly believe that you are commited to your product, and I have no problem with that.. But tests have shown in colder climates Radiant Barriers are minimally if at all effective.. As far as you keep stating no one wll take you up on your offer, perhaps because most people dont have the time for your nonsense..

Last thing, being that I sell fiberglass, wholesale, to a large portion of the contracting field in this area, and already have the outlet to distribute any type of insulation product, dont you think that If I or any of the actual experts in this area thought RB's were worth installing we would sell them along side our other products.. The reason we dont sell them is we know they are not effective in colder climates....

By the way, I have never tried to sell one person anything here, only offer free advice, unlike yourself.. So if this makes me a horrible person in your book so be it :-))

Have a nice Day

Jim
 
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