Replies

1. GBA Editor
   Martin Holladay | Dec 10, 2009 11:59am | #1

   Larry,
   Yes, it is possible for recessed can lights in cathedral ceilings to cause condensation problems.

   Recessed can lights should NEVER be installed in a cathedral ceiling.

   A cathedral ceiling needs an impeccable air barrier and thick insulation. Any interruptions in the air barrier or reduction in the insulation thickness is an invitation for trouble.

   Here's the mechanism: When your can lights were installed, holes were cut in your drywall ceiling. Warm, humid air leaks through the crack between the drywall and the can light. Water vapor that piggybacks on the exfiltrating air condenses on the cold roof sheathing. This condensation then drips down and soaks the insulation and stains the ceiling.

   While some builders advocate using "airtight" cans, I don't. So-called airtight can lights aren't really airtight.

   The best solution is to remove the can lights and rewire your ceiling for surface-mounted fixtures — for example, track lights. Restore insulation to the areas where the can lights used to be. Then repair any damages to the ceiling air barrier.

2. 
   MICHAEL CHANDLER | Dec 10, 2009 06:54pm | #2

   Martin is right of course, but yet another alternative is to replace the can trim with one rated for use in a shower that has a gasketed ring and a glass lense to form a seal at the Sheetrock. You'll at least reduce the amount of condensation dramatically but you won't eliminate it.

3. 
   JJ | Dec 12, 2009 02:45pm | #3

   Larry: TCP makes a retrofit kit for recessed can lights which seals the fixture from below, the retrofit kit replaces the bottom part of the existing recessed can fixture which makes it airtight. No drilling or cutting of the existing ceiling drywall is required, you simply remove the existing bottom part of the fixture and replace it with the retrofit kit assembly. The TCP retrofit kit includes a CFL light bulb with a variety of wattage/brightness/dimmable choices. Contact TCP at http://www.tcpi.com or via TCP customer service at 800-324-1496. The retrofit kits come in two varieties, "Universal" and "Juno/Halo" types; TCP customer service can suggest which is best for your application depending on your existing recessed can fixture make and model.
   When I bought my house, it came with 20 recessed can lights each using an incandescent light bulb in the cathedral ceiling, giving rise to an unfortunately spectacular waste of heating and cooling and lighting energy. I retrofitted all with the TCP retrofit kits; a subsequent blower door test confirmed that the recessed cans in the cathedral ceiling are now airtight.
   If your existing recessed can fixtures are IC rated, it is possible to add insulation above the fixtures, post-retrofit (however mine unfortunately were not IC rated).
   The incidence of these very air-leaky recessed can fixtures in ceilings in our country's existing housing stock is very common; the heat generated by their incandescent bulb makes each a mini-chimney which draws the conditioned air out of your house and moves it into the outdoors. This is one of the more quick and cost effective fixes a homeowner can accomplish in improving household comfort and air quality and energy efficiency.
   TCP can direct you to one of its local dealers; alternatively one of their internet dealers is http://www.goodmart.com click on Lighting Fixtures, click on Recessed Can Fixtures, and click on CFL Retrofit Trim Kits. Most retrofit kits are available for less than $40 each.

4. 
   Larry | Dec 13, 2009 09:27am | #4

   I had a roofer & general contractor look at the problem.What we found is the contractor who did the
   job did not install a ridge vent,and not enough soffit vents.All the heat from the lighting is being trapped,no place to vent.Does this make sense?

5. 
   Robert Riversong | Dec 13, 2009 11:08am | #5

   Larry,

   The lack of a continuous vent route certainly exacerbated this problem and, depending on your climate, it would contribute to ice damming.

   Your problem is not heat, but humidity - or rather lack of air sealing at the ceiling plane. It makes no sense to install can lights in a cathedral ceiling which, because of it's height, is the most vulnerable ceiling to exfiltration of moist air.

   I would advise removing all can lights, air sealing the pentrations, and replacing them with surface-mounted lights.

6. 
   Robert Riversong | Dec 13, 2009 11:11am | #6

   Larry,

   I should have added: I also advise correcting the lack of roof venting. See the study abstract I quoted in https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/15622/cathedral-ceilingroof-ventilation

7. GBA Editor
   Martin Holladay | Dec 14, 2009 09:07am | #7

   Larry,
   If you add a ridge vent to your roof, you will make the problem worse, not better. A ridge vent will encourage the flow of air out of your rafter bays, and this air will be replaced by indoor air leaking through your can lights.

   It is essential that you provide a ceiling air barrier. You must make it as airtight as possible. In my opinion, ventilating a cathedral ceiling with your symptoms is more likely to make the problem worse than it is to alleviate the problem.

8. 
   Robert Riversong | Dec 14, 2009 10:51am | #8

   Martin,

   Since we don't know what climate this is in, it's not possible to make such a definitive statement that "If you add a ridge vent to your roof, you will make the problem worse."

   We both agree that the first step should be removal of the can lights (others suggest tightening them, but that eliminates the air flow and not the heat loss).

   It could well be that getting air to move under the roof sheathing would distribute any localized moisture problems enough to allow safe absorption and release and eliminate the ceiling wetting.

9. 
   David C. James | Dec 15, 2009 05:32pm | #9

   I agree with Martin Holladay "Recessed can lights should NEVER be installed in a cathedral ceiling".

   Although In our area they are very common, my issues is with recessed lights (MR16-AIC, 7 1/2") installed at 2 x 8 vaulted roof assemblies, they have no insulation value even if they are "air tight". Thus leaving an open door for heat, cold and moisture to pass through.

   We recommend ( non vented applications) using a 5 1/2" squat-can light, thus leaving room to insulate with a minimum of 2" of Icynene between the underside of the roof sheating and the top of the can light, keeping an effective air barrier at the underside of the roof sheating.

10. 
    Larry O | Dec 16, 2009 11:48am | #10

    In a central or northern climate, the condensation issue is a common cold weather problem when the lights are OFF. The metal body of the recessed can is cooled by the attic cavity. The warm, moist room air then condenses on the metal (just like on your windows but sooner because the air in the peak of the room is warmer). Energy is also lost year round into the attic as room air leaks upwards. As others have stated, do not penetrate the vapor barrier.

11. 
    homedesign | Dec 16, 2009 12:14pm | #11

    Larry O
    "others" did not say vapor barrier...
    "Others" said AIR barrier