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Old 02-23-12, 10:46 AM   #1
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Default Air sealing around can lights. Ideas?

Kinda new here, mostly lurking.

We had an energy audit and found that the can lights leak a pretty fair amount, no suprise there. The cans are "airtight" for use in attics with insulation. We have R49 blow in cellulose installed.

So I went into the attic with a can of foam and the lights are installed with spreaders that go from truss to truss. How to foam these in effectively is a mystery to me. Building a foam box around them would seem to reduce the amount of insulation and defeat some of the purpose.

So is there an effective way to seal on the living room side of the light effectively? I'm thinking a flexible stick to absolutely anything tape or maybe caulk with some sort of needle tip to get well into the very tight crevice between the can structure and the ceiling drywall.

What is the best way(s) to seal up these leaks?

Oh, and with Great Stuff, I like the window version for most everything. It stays more flexible so when the structure moves a little it doesn't allow leaks to develop like the other more rigid foam. Hey, might as well get the maximum benefit, right?

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Old 02-23-12, 02:45 PM   #2
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Assuming that your cans are AT IC (air tight, insulation contact) rated you just cover ANY POSSIBLE crack, gap or seam in the cans including, in particular, where the can meets the drywall with spray foam. That's about it. If they aren't IC rated then you have to build a box around each individual can. I suppose you could use rigid foam but I usually use drywall. It has to be a couple inches away from any part of the can. So you cut a sheet of drywall which is the width of the joist bays from outer side to outer side plus the height of 2" above the ca from the ceiling x 2 in length and 4" wider than the can. Then you make cuts on one side of the sheetrock at the length of the height measuring in from both ends. Only cut one side. Then break it there. You have created 3 sides of a box. Put it over the can screwing it into the joists from the sides opposing the can. Then you cut a vaguely T shaped piece of sheetrock which is the width width and height of the bay for the bottom part of the T and is wider and taller than the three sided thing you made earlier. Nestle it in the bay and screw it into the earlier three sided thing. Repeat on the other side. Then foam the hell out of any seam, including the seams which are not cut all the way through. Or just tear them out, sell them on craigslist and replace them with IC rated cans. They only cost about $20 each I believe.

Clear as mud?


The one part foam (or two part for that matter) for doors and windows is low expansion. You cover significantly less area with it can for can. I never, ever, use it for any application other than doors and windows. Really, just get a cheap one part gun and get some real gun foam, like Pur or One Touch. It's a LOT cheaper in the long run (ROI is probably only about 20 or so cans of Great Stuff) and it's much, much better. I haven't seen window foam being more flexible. In fact in my experience it's more frothy and friable than regular expansion foam.
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Old 02-24-12, 09:48 AM   #3
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S-F thanks for the response. Yup the cans are AT/IC rated but are still leaking per the IR pictures and the interpretation from the guy that did the survey. It looks like a corona of air flow radiating from the can. Trying to foam with a can and the straw, I just can't get into all the areas between the can and the drywall and the truss from the attic side.

It appears that the can itsself is sealed well but I could be wrong on that. I'm guessing the air flow is coming around the can between it and the hole in the drywall.

I'm wondering if anyone has any good ideas on material and method for sealing from the living area side. You know, stopping the air from even getting past the can penetration of the drywall in the first place.

There are a couple of reasons why I want to explore this method of sealing. 1) It's probably easier that getting into the attic. 2) Cans are sometimes placed in locations where we cannot even get to the attic space like some cathedral ceilings or with other obstructions. 3) It's a common area of leakage. If you've got cans, they probably leak. 4) If it is easy and effective, others are more likely to do it.

Ideas anyone?

If anyone knows if "sealed" AT/ IC cans are still typically leaky, please state so. Then the only solution is a foamed in box in the attic to solve the probelm, OR spraying the whole can assembly and junction with Pur or One Touch I suppose.
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Old 02-24-12, 12:15 PM   #4
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I suppose there's no reason why you couldn't caulk the ring of the can to the ceiling. But that's going to be no replacement to properly sealing from the top. Get a foam gun and just dump it all over the can and all wound it. Don't worry if it looks like a head of cauliflower afterwards. That means you did it right.
All can lights a leaky. AT cans are a little better because they don't have slits and openings all over the place. They're still pretty bad. All you can do really is cover it with a monolithic cap of foam that extends to the ceiling an inch or more around it.
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Old 02-24-12, 07:07 PM   #5
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I have actually just completed doing exactly this job for a customer. The potlights are about 25 years old in a cathedral ceiling, and were equipped with 75w incandescent flood lamps.

The first part of the upgrade involved a combination of foil tape and duct seal compound packed into the corners and crevices. Then I installed a layer of self adhesive foam insulation with a foil face. These particular fixtures consist of a galvanized box with a cast aluminum reflector and trim ring, so the insulation was relatively easy to install.

The second part of the project was to replace the lamps with dimmable CFL floods, aside from the energy savings they operate much cooler and set up a "less intense" convective air flow through the fixture and into the insulation.

I personally don't like seeing pot lights in an insulated ceiling, the continuity of the insulation and vapour barrier always seems to be a compromise, not because it's overly difficult to do, it's because no one seems to take responsibility for doing it right: the electricians don't worry about it, the insulation guys shrug their shoulders, and even most Building inspectors don't look too hard. There is also confusion about the definitions, many cans are suitable for direct contact with insulation, so people assume that they are vapour tight when in fact "vapour tight" is a distinct and separate specification.

The reason we did this work on these lights is because, as I mentioned, these lights are in an insulated cathedral ceiling, and the hot air travelling through them warms the roof and shingles and melts the snow. You can actually see the location of each and every light in the house. The snow melt causes a serious icing problem at the eaves.
This is the first step, and is moderately succesful. The next project is a new steel roof, complete with a new layer of insulation to be installed later in the spring of this year.

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Old 02-24-12, 07:32 PM   #6
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Hi,
I did a little research into the proper way to seal can lights. I installed Juno can lights in our house. So I contacted their technical dept. and got the following reply:

"In response to your inquiry regarding the use of spray type foam insulation with Juno IC
rated fixtures.

Based upon our Engineering Department's review, we cannot at this time recommend the use
of spray foam. Expansive testing would need to be conducted before such a recommendation
could be given. Our initial concerns are primarily related to the expansion during
installation. Great precautions would have to be used to insure that the housing and
junction box cavities were not penetrated thus preventing access and/or infiltration of
this product to the inner workings of the housing (i.e. socket, wire or thermal device).

Please call our Technical Service department with any questions"

So in regards to your question (below)

[If anyone knows if "sealed" AT/ IC cans are still typically leaky, please state so. Then the only solution is a foamed in box in the attic to solve the probelm, OR spraying the whole can assembly and junction with Pur or One Touch I suppose.[/QUOTE]

I would recommend the safe route and do as S-F suggested and use a sealed box around your fixtures. It is the safest route. A side benefit of drywall is that it is can be fire rated material.

My problem with boxes is that, if you have 16" of insulation in your attic and the box is 14" tall, you would only have 2" of insulation over the light. Then again the easy solution to that problem would be a few layers of rigid insulation and some spray foam.

Sometimes you have to just do what you can. If you have recessed lights in a cathedral ceiling you might try taking the trim ring off and use silicone to seal the drywall to the can. There may be other leaks, but everything helps.
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Old 02-24-12, 09:57 PM   #7
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Thanks for the responses everyone!

I really like the idea of slobbering foam all over the top of the unit like S-F says, as it can't help but to seal everything up. The response from Juno is par for the legal department, real world is another matter though I'm sure. If CFLs were exclusively used the thermal risk is probably pretty low. However a 120 watt incandescent could probably be mistakenly screwed in and when operated for 24 hours on a 110 degree day without air conditioning there could be some problems, at least some bad smells. We're dedicated to using only CFLs so it shouldn't be a problem for us.

The other really good thing about foaming the whole can is stopping any vapor transfer. That is something I hadn't considered.

I guess I'll look for a good place to buy some Pur or One Touch. Any suggestions for great deals?
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Old 02-25-12, 09:59 AM   #8
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Certain fixtures are rated for insulation contact. I'd be nervous to cover one in spray foam since its flammable. I suppose the 'fireblock' stuff might be fine. Hopefully S-F will chime in again on the fire safety aspect. The holes in can lights are to allow the heat to get out and the boxes that CFLs come in say that they shouldn't be in a sealed can fixture. I've seen plenty of youtube videos where they surround these with drywall(fire rated material) and then spray foam around that. I've also seen others where they just make a rigid foam box around it, probably not to code but if there is enough space it would be fine for a CFL. If these were in the attic and you were blowing in cellulose then you'll have a chance to cover a drywall enclosure too.
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Old 02-25-12, 12:49 PM   #9
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I just used my IR gun on the white painted reflector of the can. I stood on a chair and pushed the gun up inside the reflector to maximize the accuracy of the reading. The light has been on for 3 hours. The temp was 117*F. It's 35*F outside, there is R49 around the can and probably R10 or so above it. I do not have temperature of the exterior of the can, but I'm sure it's less.

Anyone know the high temperature at which spray foam begins to degrade?

The Great Stuff site says the working temp range is up to 120*F, but after it's cured I'm sure it's different.
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Old 02-25-12, 09:25 PM   #10
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If you have an IC AT can there is no reason not to literally cover it with foam. Completely. 100%. The drywall box is only for non IC rated cans. Making those boxes sucks. Just get new cans. If you wire them yourself it's less work than making those damn boxes and it works a LOT better. As to degrading spray foam: I only use two kinds of spray foam. One is for windows and doors, and I ONLY use it for windows and doors if I can help it. Sometimes the bean counters order cases of the stuff and that's all I have to use, and that sucks because it's lame stuff. The other is fire rated. It is code rated as a fire block between floors and the like but it's not ASTM E136 rated so you can't put it against a hot pipe or a chimney or something like that. If it gets too hot it will melt (seen it). There really is no reason to get any other kind of foam (Unless you are doing a window or door). I'm not sure about the consumer price but with a contractor account at Tiger Foam the price of fire rated and non fire rated foam is the same.
@ beatr911. Don't stop moisture movement. You want the house to be moisture permeable but air impermeable. The other day someone opened up my dishwasher. I have never used it to wash dishes but y son likes to "play" with it. It gets 1/2 filled with water and then after a couple weeks it gets plain rank. Like a sewer. Then I have to run it just to get the swamp out. The point is that we didn't know all of the fury of hell was festering in there. because it was vapor impermeable. Let it "breathe" moisture but not air. You don't want moisture condensing anywhere in your house except in you condensing dryer or boiler.

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