Replies

1. 
   Mongo_ | May 23, 2001 09:11pm | #1

   *
   Tim,

   My thoughts...

   1) Some advocate using RFBI for boxing in cans. I prefer to use drywall. Make a simple drywall box, using duct tape to hold it together. Once assembled, hit the seams with a can of spray foam to seal the box. Don't forget to seal the bottom of the box against the upper surface of the ceiling below. The idea is to make it tight, no air infiltration. Which leads to...no air holes for ventilation. Proper bulb size, box sizing, and the can's IC feature will take care of the heat.

   2) If you're stuck with tall cans (no low-profile available), instead of increasing attic floor depth with board insulation, why not just furr it up with 2-by stock? Run 2-by stock perpendicular to your attic joists, 16" OC, or as desired. You can either lay 2 x 4's flat, or rip them into true 1.5" by 1.75" (not taking into consideration blade kerf loss)lengths. A dollop of construction adhesive along with your fasteners will hold it tight. That will increase your depth by 1.5" (or slightly more if you flip it...1.625"-1.75"ish?) and will allow solid wood-to-wood contact instead of a less stable RFBI sandwich.

   Since you're going to blow part of the attic, why not blow it all? Forget the FG batts. Once the furring is in, blow cells in everywhere. Once the insulation is in, set your decking, nailing it off on the furring.

   Before proceeding, pull up any insulation now in your attic. Use expanding foam to seal any and all holes in your attic platform (wiring, plumbing, mechanicals, sloppy construction, etc) that lead to the living spaces below. Small effort with sometimes large returns.

   Good luck.

1. 
   timbo | May 24, 2001 04:52am | #2

   *Thanks.... I appreciate your thoughts............ How big should I build the boxes? What is the minimum distance to stay away from the can? Thanks again... Tim

1. 
   Crusty_ | May 31, 2001 07:08am | #3

   *Polyiso foam board will burn pretty easily -- it's normally labeled as "do not leave exposed." But you could put it on the outside of the drywally boxes if you want (won't need it if you're going to have insulation all around).I'm faced with exactly the same situation. My cans are actually pretty tight as they're made in one piece (an extrusion process, kind of like with a coke can). There are some depth adjustment slots and some slots in the top where they made the "temporary" brackets to hold the sockets up out of the way. I will cover these from the outside with foil HVAC tape. That will take care of the air leakage, so the boxes won't need to be air tight -- just keep the cellulose away from the cans. The cellulose could be sprayed right over the top since it won't burn, but the lights would turn on and off and they got hot and then cooled down.Drywall will work fine and you can score and snap it pretty quickly. Duct tape? Hmmm.... Would construction adhesive work as well? I will probably use 1x2's to make a single frame that will go around the middle to stiffen it up.

2. 
   tim_patterson | May 31, 2001 07:08am | #4

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   I am building my house. Preparing for insulation. I have these questions. part 1
   I have IC rated cans but still want to keep a distance between them and the insulation. Is building a box out of foam insulation board the way to go. If so should I provide holes for the heat build up to release. Any ideas would be appreciated. part 2........These cans are above ceiling joist height on the attic side. I want to deck part of the attic so I thought boxes would work well with decking. I have 2x6 joists . I live in the middle Tennessee area. Should I deck first within Insulation board [what thickness]and then cover that with plywood and put bats between the joists. Or are bats good enough. I will blow the edges where there is no ceiling height in the attic. Thanks for any and all thoughts.