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Radiant Barrier sprayed on or glued on roof how to get rid of or fix.


Tim T.'s Avatar
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11-08-11, 10:37 AM   #1  
Radiant Barrier sprayed on or glued on roof how to get rid of or fix.

I am planning on putting insulation and a air conditioner in a tuff shed. I bought the radiant barrier package thinking it would help cool it. The last few months as it worked on it I came to the conclusion this tuff shed is a oven (live in so cal), its getting much hotter than the other tuff shed we have. So I put my hand up to the barrier foil sprayed on and it felt real hot, I compared it to regular tuff shed siding inside and it was much cooler.

I did a little research and found that radiant barrier osb sheathing sprayed on and it appears it actually raised the tempature and will probaly shorten shingle lifespan.

My plan was to glue 2-3 inch strips of foam board onto the barrier (leave a inch of air space). Then put in batting sort of cathederal style r13 insulation. Will this work?

Now I am thinking will the foam catch on fire if I put it right next to the radiant barrier board? is there a way to get rid of this barrier stuff can I peel it off or a work around since it is installed already?

Dont know what to do please help!
Thanks in advance for any help!

 
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Bud9051's Avatar
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11-08-11, 11:30 AM   #2  
A radiant surface on the inside of an osb roofing will cause the osb to get hotter because it can no longer cool to the radiant side. That's normal. Catching fire I would doubt. Shortening the life of the shingles, supposedly not, as in the case of a total hot roof. Ideally, the radiant surface would be the shingles, so the heat never becomes part of the equation. Blocking it at the osb does raise the temperature of the material, but it is that or deal with it on the inside, ie air conditioning or venting.

Even adding a perfect layer of insulation on the inside will have the same effect of raising the osb temperature, as the heat has once again been trapped.

As for your planned insulation, I didn't follow. As for eliminating the RB if you decide to go that route, paint it.

Bud

 
equinox's Avatar
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11-08-11, 02:08 PM   #3  
Depending on budget and your needs you could also consider creating an insulated attic space by installing a ceiling if there is enough height and if you are not using that space. If you did that you could vent it properly to add air flow that perhaps you do not have at the present time and any AC that you installed would be more effective and efficient. Just another way of thinking I guess.

 
Tim T.'s Avatar
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11-08-11, 06:18 PM   #4  
thanks replies and help

Thank you for responses,

radiant surface on the inside of an osb roofing will cause the osb to get hotter because it can no longer cool to the radiant side
Ok I am not %100 sure I understand but I think your saying usually part of the heat goes out the roof through the shingles of a regular osb board. The osb barrier radiant foil traps the heat and sends it into the building which makes the building hotter. Which is sort of opposite of what it is advertised to do which is making the building cooler.

Bottom line I think I am correct in saying the inside of my building is hotter because of the radiant barrier, it would be cooler without the radiant barrier attached to my shed osb roof.

IF I paint it is there a better paint to use or color, is a dark color better to use or a lighter color, would kilz be better than paint etc?

Another option I noticed was some rips in the foil it when they nailed the roof on. I looked cloesely today it is actually appears to be glued on and I can peel it off somewhat (although sort of a pain) would this be better than painting or doesn't really matter either way. When I do peel the foil off it appears there is a glue like liquid nails underneath which I assume they used to attach to the osb board.

consider creating an insulated attic space by installing a ceiling if there is enough height and if you are not using that space. If you did that you could vent it properly to add air flow that perhaps you do not have at the present time an
That is a option I guess, I plan on adding insulation I just wanted to do it between the 2x4 on the ceiling sort of wanted cathederal style because it is a small 10x12 shed and I like a higher roof.


How To Install Radiant Barrier In A Cathedral Ceiling - YouTube

I was planning on using this trick above Around the one minute mark to make a air space between the radian barrier foil and my batted insulation using foam board between the batted insulation and the osb radiant foil. I went ahead and cut the the foam board and was ready to install when I wondered if the foam board could heat up being next to the radiant foil. Since heat from the roof is passing directly into the foil. I also wonder if the heat would just carry through the foam board into the insulation. In otherwords the video shows the proper use of the foil, my going
roofing osb foil foam gap insulation, not sure would work. whew sorry so long.

Anywho I think I am best getting rid of the barrier stuff and adding insulation normally, Thanks for additional help!

 
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11-08-11, 09:13 PM   #5  
IMO, keep the RB and add insulation normally.

Let me try again on where the heat goes with a RB on the bottom of the roof deck (OSB). Sun heats the shingles, shingles heat the osb, and osb heats the foil. But the foil cannot radiate much of the heat to the space below, so it continues to get hotter. That heat raises the temp of the osb and shingles which then dissipate more heat to the outside via radiation and convection. On the inside we still have a hotter foil surface, so convection kicks in and begins to heat the air inside. The RB will have effectively reduced one of the two means of heat transfer, radiant, but convection will still be in play. This now requires isolating the warmer air (sheetrock) and insulating the room below from its build up. The next step is to exhaust that excess heat with incoming soffit air that gets warmed and pushed out an upper vent, usually ridge vent.

Since fiberglass insulation still allows some air to flow through its fibers, the heat will still be able to sneak down through more than what the r-value might suggest. Mineral wool has a much greater density and acts as a better air barrier as well as an insulator. Depending upon your cavity height, 2x6 I'll assume, you simply tuck in a 3.5 inch layer of insulation, cover with a vapor barrier and sheetrock, and you have the air channel needed between the insulation and the osb.

The benefit of the foil would be preventing some of the heat from entering cavity between the insulation and the osb. Yes, it raises the osb temperature, but that increases the heat loss back to the outside and reduces the work of the venting.

Whether rigid foam can stand up to the temperatures in that space or not, I can't say. I have seen it shrink when exposed directly to sun light, but that includes the UV.

Bud

 
Tim T.'s Avatar
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11-09-11, 12:17 PM   #6  
Thanks for help!

Thanks for taking the time for the clear explanation that made it much more understandable.

I think I got the big picture, make a air flow channel between the osb rb and my insulation using vents.

Any problem using 2 sided batt for my insulation (thats what we have previously purchased or is one sided better?

One question on the vapor barrier, First what is it, is it just a thick peice of plastic maybe 6 mil?

I read in certain climates don't use a vapor barrier I am in Southern California would it still be advantageious to use one here?

Not sure where the vapor barrier would go this is from top roof down
would it be this order:

1. roof.osb rb
2. air gap vents
3. vapor barrier
4. batting
5. drywall

or would it be

1.roof osb rb
2. air gap vents
3. batting
4. vapor barrier
5. drywall

Thanks in advance for all the help, sorry I am very much a newbie in this area!







Double checking order

 
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11-09-11, 12:28 PM   #7  
Forgot you are in CA. With a mostly ac climate the vb would typically go on the outside. But the foil rb, regardless of its condition is still a functioning vapor barrier, and perfect is not necessary. Omit adding any additional plastic barriers.

Not sure what you mean by 2 sided batts. If it simply the batts in a perforated bag, so to speak, no problem. I have never seen Kraft on both sides so I don't think it is that. The issue would be too many vapor barriers if whatever is on both sides of your insulation is acting as a VB.

Bud

 
Tim T.'s Avatar
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11-10-11, 02:55 PM   #8  
thanks reply again

Ok I went and looked again The last shed I did insulation in was a year ago, I am wrong its just one side with the carboard type paper as you said it, the other side is pink fiberglass on the outside.


Stuff thats looks like this video only its R13
http://www.youtube.com/watch?v=tuW033vM-xA My Guess is the paper side goes down and is next to the drywall as in the picture and the fiberglass is facing upward toward the roof, or maybe I am wrong again?


Thanks again for the help!

 
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11-11-11, 11:19 AM   #9  
I always thought that any vapor barrier/retarder needed to be on the warm side, which varys by region, or in some climates that were in the middle zones that they were not required at all any more. If the shed is air conditioned then the hot side is the outside in a warm climate zone depending of course on where in the state it is, and how often the inside would be cooled.

 
Tim T.'s Avatar
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11-12-11, 11:07 AM   #10  
Hmm interesting

I found this article from building sceince which basically says what you are saying

[QUOTE]In general water vapor moves from the warm side of building assemblies to the cold side of building assemblies. This is simple to understand, except we have trouble deciding what side of a wall is the cold or warm side. Logically, this means we need different strategies for different climates. We also have to take into account differences between summer and winter. [/QUOTE

whew I am not going to be running the air conditioning more than maybe 10 hours a week, While its running inside the building it would be the cool side. However when the air is not running (most of the time) I assume the hot side is the roof side. So I should base it on hot side being outside I guess.


Thanks replys and help

 
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11-12-11, 02:17 PM   #11  
It sounds to me that as you will not be heating the space during the colder months, so the only time that you will have a hot to cold difference is in the summer when you apply AC. To me then it makes sense to keep any vapor retarder on the outside of the insulation to help prevent condensation which will lead to potential mold conditons forming. The different approach between climate zones around barriers is taken due to both heating and AC requirements and how many months cold or hot is part of that equation. When it is equal they are now recommending I think not to use a barrier at all and to let the air flow through the thermal break as a compromise conditon. I am not sure why also you would not insulate the walls also at the same time to keep energy costs lower and to have better AC results as well.

 
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11-12-11, 05:00 PM   #12  
Radient barrier is usely a waste of money unless your in Florida

 
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