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Is Cellulose insulation allowed to go where fiberglass cant?


rugsr's Avatar
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Join Date: Sep 2008
Posts: 80
NY

11-30-09, 05:53 PM   #1  
Is Cellulose insulation allowed to go where fiberglass cant?

Hi all, Im adding insulation to my attic and I have a question.

See I installed a light above the shower and the directions said to remove 3" of insulation around the light canister. Doing that prevents a fire but I can feel some cold air coming through (Buffalo NY)

I have heard that Cellulose insulation is fire proof, this true? If so, can I go up there and put the cellulose all around the light canister?

The insulation im adding is R30 covered in plastic, cheap at HD. In between the soffit and the R30(the void) im adding cellulose.

Since i dont have much to do im adding cellulose by hand. I am making sure i break it apart before i put it in.

Think its even worth adding the celllulose?

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Bud9051's Avatar
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ME

11-30-09, 11:34 PM   #2  
Hi rugsr,
The short answer is no, the cellulose or fiberglass insulation must stay 3" away from a non-insulation contact rated light fixture.

What you would like, especially since this is over a bathroom with all of the moisture, is an "air tight" IC (insulation contact) rated light. Then you could seal it to the sheetrock below and bury it in insulation. Do some research on this, but I have seen boxes constructed of sheetrock, maintaining the 3" clearance, built over the lights. The research is needed because enclosing them seals the air flow and they may need that to stay cool.

Once the light can is replaced or protected, you can bury it in insulation. Replacing it with the proper fixture is the way to go.

As for adding cellulose by hand, it needs to be blown in to achieve the dense undisturbed properties that help it insulate. Fluffing it up opens up air paths so it's net r-value would be lower. But, if it will fit where you want it, usable.

You mention the R-30 is plastic covered. If that is a vapor barrier, then it cannot go on the attic side of the insulation. If it is perforated, and just plastic covered to make the fiberglass easier to handle, that's ok.

Now before the insulation goes in, the most important step is to air seal all of the holes for electrical wires, plumbing vents, and chimneys. Also cavities above drop ceilings or other wall to ceiling openings that allow air to pass through walls from conditioned spaces below into the attic. Use a fire rated caulk or foam and metal flashing around chimneys with silicone to seal it.

There, that should keep you busy, and warmer.

Great Stuff has a page with a short list of where air sealing is good. http://www.greatstuff.dow.com/pdfs/checklist.pdf
Bud

 
rugsr's Avatar
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12-01-09, 06:23 AM   #3  
thanks bud,
yea the light i have is made to go above the shower but they dont make them IC. all the shower recessed lights are Non-IC.
Ill have to look into building a box of somesort.

Yup the r30 is the kind that makes it easier to handle

As for sealing up the holes where wires go through 2x4s etc...how important is this if all of that is covered by 2 layers of insulation anyways?

thanks

 
Bud9051's Avatar
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12-01-09, 08:13 AM   #4  
If it were covered with at least 3" of blown in cellulose, then the cellulose would help to reduce the air flow, but it must be blown in to be dense enough. As for regular fiberglass, slow moving air goes right through it, thus the air sealing is rated as perhaps the number one energy improvement to make. That assumes you have some insulation. Now, I have to say, I have no idea as to how the fiberglass in plastic will do, but I suspect it cannot be taped and sealed well enough to restrict air movement. Beyond the heat rising and the wind blowing, a home actually inhales and exhales as the temperature changes. That breathing effect constantly forces warm moist conditioned air into the walls and on up and out through the attic. The only way you can seal too much is if you are there as the building is going up and seal everything. Otherwise, you do the best you can, but the benefits are better than the extra insulation you are adding.

Bud

 
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