Trying to seal my attic. I’m thinkng about building foil faced rigid foam boxes around the can lights and gluing the panels together with expanding foam, essentially creating a 5 sided box I can flip over and seal around the lights, using the studs as additional support…..Will this work? I worry it will get to hot and set off the wattage regulators and I’ll have to punch a few holes in the box to let out some heat, which will take me back to square one. I’ve actually held a lighter to this foam and it will not burn or ignite as far as I can tell. Even thought about bypassing the regulators altogether, although I’m guessing this isn’t adviseable. I like the box idea though. It seems to me that IC can lights are no different than the cheapo cans, they just dont have holes in them. Ideas?
Edited 12/4/2004 4:33 am ET by hillside
Replies
I'm assuming that your fixtures are thermally protected but not rated for direct contact with insulation. Just go ahead and build your box the way you describe. Don't punch any holes in it as heat build up will not be a problem providing that you have not 'over lamped' the fixture. The correct light bulb type and wattage is determined by the combination of the can and trim as a unit. Don't bypass the thermal protection under any circumstances.
John
Edited 12/4/2004 6:43 am ET by england
I don't know if I would use the foam to build the boxs, I have seen them made out of 5/8" drywall before. If i remember right they were 22 1/2 x 22 1/2 & the same tall, fit between the truss bays.
on my ic lights,i went around and sealed all the small gaps in the can with silicone,then laid fiberglass ins around them,then blew cellouse about 12" over them. i hope that slows the air flow some.i did have trouble popping the thermal breaks with plain ol 100 watt bulbs that i threw in while const. was going on. but now have 75 w bulbs and every things fine. i had planned on doing something like your talking about or taking a 5 gal. can and cutting 1 end out and placing over the light,but just got lazy and went on. can lights have to be one of the biggest air leaks in a house. i'm surprised that someone doesn't make a really good airtight with ins. already in place. larry
We box cans out frequently for fire rating just like G80104 described,firetaping seals it up.Oversizing it is important,or the bulbs will overheat and blow.It is easiest done before rocking the ceiling,but can be done from the attic,just firetape and add foam over the top(outside of the box).Mike
Edit-I am always thinking of commercial situations,if you are on a lower floor the box might not work.When I remodeled my house I used lights rated for insulation contact.
Edited 12/4/2004 11:09 am ET by Ruffmike
I've heard these boxes are normally built with duct board, sealed with fire-rated mastic. I would not use expanding foam in any high-temperature situation. You should be able to get duct board in small quantities from a HVAC contractor.
I have a similar situation with an infra-red lamp. Ic-rated but it's got a fan to cool down the lamp and ventilation channels on the sides. I wouldn't buy a recessed light unless it's ic-rated airtight, but no such beast for infra-red lamps that I can find.