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Old 09-27-2008, 11:00 PM   #1
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vapour barrier over ic housings


I'm getting some confusing advice on the subject of air sealing an 'air tight' ic housing - the problem being that 'air tight' isn't really air tight.

An insulation contractor suggested building a drywall box over the housing and encasing it in a couple of inches of PU foam. Supposedly the drywall is needed to provide the necessary fire break. Seems like a lot of work.

Various manufacturers sell a kind of plastic box with flanges to enclose the housing before the drywall goes up, but if you're installing the light on an existing ceiling, the flanges around the edges of the box don't sit on the drywall and are therefore hard to seal. Presumably you could seal the edges with foam, but again you would would seem to have the problem of foam with no fire break.

Any suggestions?

Thanks,
Paul N.

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Old 09-27-2008, 11:09 PM   #2
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You mentioned fire breaks a couple times. Are you installing the cans in a rated floor/ceiling assembly or in a rated ceiling? The reason I ask is that there isn't a fire break or fire penetration issue in single family residential, except in the garage. The drywall box method you described is often employed when the can is being installed in a fire membrane (like an attached garage) or fire assembly (like in a multifamily structure).

As far as air sealing goes, remember that an IC can is designed to have insulation piled around it. That's opposed to a non-IC can, which can't have any insulation within about 3" of it. Being IC doesn't mean that it won't get fairly hot before shutting off though, so I'd caution you against deliberately putting materials against it that might melt.

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Old 09-27-2008, 11:21 PM   #3
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vapour barrier over ic housings


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Originally Posted by thekctermite View Post
You mentioned fire breaks a couple times. Are you installing the cans in a rated floor/ceiling assembly or in a rated ceiling? The reason I ask is that there isn't a fire break or fire penetration issue in single family residential, except in the garage. The drywall box method you described is often employed when the can is being installed in a fire membrane (like an attached garage) or fire assembly (like in a multifamily structure).
It's not a fire rated ceiling - I presume the insulation guy was referring to the need to have a fire rated material such as half-inch drywall between PU foam and a living space.

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Originally Posted by thekctermite View Post
As far as air sealing goes, remember that an IC can is designed to have insulation piled around it. That's opposed to a non-IC can, which can't have any insulation within about 3" of it. Being IC doesn't mean that it won't get fairly hot before shutting off though, so I'd caution you against deliberately putting materials against it that might melt.
Right - so I presume that's the reason why PU foam can't be applied directly to the IC housing. Question is, can it be applied to the plastic box, which is designed to create an air space around the IC housing, in order to seal the edges?
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Old 09-28-2008, 12:13 AM   #4
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vapour barrier over ic housings


I can't picture the plastic box you're talking about. But, I can say that you shouldn't have any problems unless you put foam against the can itself...That's the part that gets nice and warm.
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Old 10-01-2008, 06:31 AM   #5
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Originally Posted by thekctermite View Post
I can't picture the plastic box you're talking about. But, I can say that you shouldn't have any problems unless you put foam against the can itself...That's the part that gets nice and warm.
As it turns out, the plastic boxes don't fit very well in the available
space and would be almost impossible to seal. The alternative
seems to be to enclose the housing in some kind of drywall box
and foam-seal the edges... a painful and time-consuming job.

The design of these so-called air tight housings seems pretty
poor to me. According to the manufacturer, they need to leak into
the insulated space so that they don't overheat. If you want
to seal and insulate them perfectly, you need to increase the
air volume in the space around them to allow the heat to disspate
(presumably back through the ceiling drywall).

Any suggestions for a better way?

Thanks,
Paul N.
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Old 10-01-2008, 09:34 AM   #6
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vapour barrier over ic housings


There are commercially produced metal box enclosures for can lights (used in fire separation applications), but they're super-expensive.

The sheetrock box idea is the best in my opinion. Just use some 1x or 2x for a frame and rock it. Easy enough, but a lot of work to stop a little air leakage.

You could also make boxes out of therm-o-pan, I'd think. It is a duct material. It is like working with cardboard. You might want to check out its flammability, but I think it is pretty much noncombustible, and will not support combustion. Edges could be sealed with caulk or foil tape.
http://www.thermopan.com/products_thermopan.htm
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Old 10-01-2008, 10:54 AM   #7
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Is there a reason why you want these things 100% air tight? Is it an inspection issue? Or just because the insulation guy mentioned it?
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Old 10-01-2008, 11:17 AM   #8
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Originally Posted by InPhase277 View Post
Is there a reason why you want these things 100% air tight? Is it an inspection issue? Or just because the insulation guy mentioned it?
The insulation guy mentioned it - but not because he wants more work. It's too messy for him, and he wants me to deal with it.

My concern is that even if it isn't 100% air tight, the attic, like the rest of the house, will be insulated above code (R50), and the comments of the manufacturer don't fill me with confidence that these things won't overheat.

Something that relies on leakage to provide thermal relief strikes me as an incredibly poor design, unless the leakage can be specified, which is out of the manufacturer's control...

Thanks,
Paul
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Old 10-01-2008, 12:03 PM   #9
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vapour barrier over ic housings


The IC cans have a thermal shutdown feature. If they get too hot, they shut down for a while. Happens all the time when people use bulbs with excessive wattage for the particular IC can they have. There's no hazard in insulating around IC cans, and the air leakage is a fairly insignificant issue in my book.
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Old 10-01-2008, 01:09 PM   #10
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Originally Posted by thekctermite View Post
The IC cans have a thermal shutdown feature. If they get too hot, they shut down for a while. Happens all the time when people use bulbs with excessive wattage for the particular IC can they have.
According to the manufacturer, they'll overheat if you seal them tight. He didn't mention exceptional operating conditions.
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There's no hazard in insulating around IC cans.
I guess it depends on the type of insulation you're using. You can't insulate them directly with PU foam (which would also seal them). So if you're using foam, the cans are neither IC or air tight.

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Old 10-01-2008, 02:23 PM   #11
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Originally Posted by pauln View Post
I guess it depends on the type of insulation you're using. You can't insulate them directly with PU foam (which would also seal them). So if you're using foam, the cans are neither IC or air tight.
Yeah, sorry. I think it is safe to say that it wouldn't be wise to put anything against them that would melt. I've got blown cellulose and fiberglass on the brain.

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