Kraft barrier and recessed light ques

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Old 01-16-04, 07:52 PM
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Kraft barrier and recessed light ques

Couple of questions for all.

I am insulating my second floor (new construction) and have several IC rated cans installed (5" incandescent, 4" low voltage MR16).

Can the insulation's kraft paper touch the light housings or should it be pulled a few inches away and removed? I just have a fundamental problem with asphalt impregnated paper coming in contact with a heat source.

What, if anything, can be used to maintain a safer vapor barrier
if I do remove a few inches of the paper?

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Old 01-16-04, 08:26 PM
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http://www.nol.org/home/NEO/home_const/details/rcld.htm

This link shows a diagram on how I insulate over recess lighting, even if it is IC Rated.
 
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Old 01-17-04, 05:36 AM
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Nice picture, thanks for the link. But that doesn't
answer the question if the lights are installed without
a boxed enclosure. The ceiling I am working with is a 4 pitched roof and as some of the lights are in the lowest part of the slope there is no room for both an enclosure and insulation above. In this location the lights are installed directly to the strapping and have about 4 inches from the top of the lights to the roof sheathing. This allowed me to run baffles from the soffit and hand fit some R13 above the can.

The collar ties and rafters are sized to fit R30 batts at the lowest part of the roof where they meet the exterior wall. So, I install R30 batts in the collar tie right to the edge of can housing and hand fit the sides of the can housing with additional insulation. I just want to know if I should keep the kraft paper 3-4 inches away from the housing and replace it with poly or something else.
 
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Old 01-17-04, 05:35 PM
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The problem with the recess lights in this application is not so much as heat transported moisture, rather air transported moisture is a major concern. The heat from the canister will cause the air surrounding it to move and create a convective loop. In other words as the warm air moves away from the canister, it will draw cooler air to it. This cycle will repeat as the cooler air that is drawn to it is heated by the canister.

So regardless if you use poly, kraft paper or anything else, if the enclosure you create for the canister is not completely air tight, that is supposed to contain the convective loop, you will have problems with your roof. The first sign will be ice dams above the area where the lights are located.

Convective loops are also found within the structure. The difference between this and the application of the recess lights is the convective loop inside the house is contained by the ceiling, walls and floor and there will be very little to contain the convective loop in your attic. Ventilation will not suffice because the recess lights are a direct heat source.

So to answer your question, it is not advisable to put any type of vapor barrier in direct contact of a known heat source. Regardless what the manufacturers say. If you cut away the vapor barrier from the insulation, you increase the probability of heat transported moisture problems. If you create an enclosure for the light and it is not completely air tight you will have air transported moisture problems. The heat transported moisture problems have a very high probability and the air transported moisture problems have an extremely high probability.
 
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