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.
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.