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Old 01-21-2013, 07:25 PM - Thread Starter
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Is it OK to build recessed light backer boxes from OSB+drywall, or is OSB+cement board necessary for fire safety?

I'm using the 4" remodel cans from Lowe's (the ones that come with a housing and white baffle for ~$16), non IC, but have a thermal cutoff switch. There are no real guidelines in the product documentation about clearances between the housing and any other materials- just 3" min from insulation.
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Old 01-22-2013, 09:21 AM
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Drywall is fine, It is what is used for firecode backer-boxes

http://intranet.progresslighting.com/firebox/Firebox.html

I like using the cement board because I can cut all the pieces on my table saw for a quick assembly. (Special blade required)
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Old 01-22-2013, 09:43 AM
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Many years ago, and engineer from USG told me that Type-X paper can delaminate with successive heating and cooling, and the paper is combustible, so that's when we started recommending cement board.

In reality, I have no idea how much of a liability (if any) the drywall is as a liner for these boxes.

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Old 01-22-2013, 01:31 PM
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I would be a little leary of using OSB for the actual box. Mainly because of it's density and attaching the components to each other when you screw them together (making a air tight seal).

I used 3/4 MDF for the box and cement siding board to line it. The cement siding worked great, was inexpensive and I only needed one stick of it to do my 6 cans. The MDF (as you know) is very dense and made very tight seals when screwed together.

Just a thought...
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