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bricks4u 02-13-2010 07:44 PM

Frost in attic
Hello everyone. I am sorry if I am not explaining this issue properly as I am a novice when it comes to this. However I have a house that is about 8 years old with a vaulted ceiling. I have noticed a large amount of frost in the attic under the soffit baffles. I think I have pinpointed the issue I just do not know the best way to fix it. I believe the issue is the recessed lights I have in the home (95% of the frost is forming right above the lights). They are IC rated lights and have insulation around them but I think they are still allowing air to leak into the attic. I was told to build a box around them or seal them however they are not accessible from the attic because they are located so close to the soffits and only have about an 18 inch gap between the roof and the ceiling. My question is can I seal these up from the inside? If so what is the best way to way to do it and what type of caulk or foam should I use? I I am able to pull the "beauty ring" down about an inch and I can see a gap that leads into the attic and I can also feel the cold air from the attic so I am guessing a lot of air is exiting this area and going into the attic. I have even had some frost melt and water come though this fixture into the ceiling! Also since some frost comes through the fixture when it melts where does the rest of the moisture go? Is it pooling up somewhere in the attic and is that going to cause further issues?

Thanks in advance to anyone that can offer their insight.

Bob Mariani 02-13-2010 09:02 PM

spray foam is the best way to insulate around these can. BUT... I never install recessed cans in a cathedral celing because you will have the problems you are experiencing. On way to avoid this is to have over sized rafters leaving room for insulation above the cans also. Without at least 2" foam above the cans the heat from the lights will produce condensation on the roof sheathing and eventually drip down to ruin the lights or the drywall.

bricks4u 02-13-2010 10:41 PM

Thanks for the input Bob. Unfortunatly I cannot do anything about the rafter height or the fact that the recessed lights were already installed. In regards to the foam would the fire block great stuff work? Keep in mind I am going to have to use this from the inside vs using the foam in the attic. I dont want it to expand and leak around the outside of the lights, would caulk work better if I plan on sealing from inside the house. Also since I have noticed the frost I have not turned on the recessed lights at all in fear of them heating up and causing frost. I have been using lamps to light up the living room for a couple months, and even without using the canned lights I am still getting frost which makes me believe the issue is coming from heat loss.

Bob Mariani 02-14-2010 08:54 AM

moisture in your attic causes:

1) a wet basement or crawlspace.... yes this is actually a major cause. warm moist air moves through the house via "stack effect". it will find any holes in your pressure boundary and work it's way into the attic where it is collected on the colder roof sheathing and condense..

2) no venting above the insulation to remove collected moisture

3) recessed cans add beaks to the pressure and thermal boundaries as well has heating frost collected on the moist roof surface

4) inadequate insulation will only contribute to heat loss and heat gain and has nothing to do with the frost problem


1) seal the rim joists in the basement or crawlspace with spray foam.

2) if on a crawlspace be sure a sealed poly barrier is over the dirt and up the foundation walls, tacked to outer plate

3) seal any electrical or plumbing penetrations with foam

4) cut a whole next to the recessed lights and spray foam around and above these cans.

5) caulk the trim of the recessed lights

6) check or fix as needed proper roof venting

bricks4u 02-17-2010 06:52 PM

Hey Bob -

I bought a can of Great Stuff Fireblock foam. Like I said in the earlier post the light is not accessible from the attic because of its location. Will this stuff work if I pull the ring down an inch and spray around the ring connected to the light? Also if I do this could it expand and make it so the ring is no longer flush with the ceiling? Just wanted to know what you or anyone else thought of this idea.


Bob Mariani 02-17-2010 07:59 PM

the foam will work. maybe use the straw size tube to get the foam around the top of the can. This area is where your trouble is. if some expands out the bottom just let it cure and then cut it flush with the ceiling.

AaronB 02-23-2010 11:28 AM

Don't recessed lights have to vent heat?

Big N8 02-25-2010 11:38 AM

Not all of them do. You have to make sure you get the correct ones for the installation you are looking to do.

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