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Recessed IC can lights in unventilated cathedral ceiling.

I'm having a log home built wth cathedral ceilings. I plan to have 1 1/2 to 2 inch closed cell polyurethane sprayed onto the interior side of the roof sheathing with blown in insulation filling the balance of the twelve inch rafter (I beam style of rafter) cavity. This wll be an unventilated roof. Tongue and groove will be used on the ceiling surface. I understand the spray foam will act as an air barrier, and the tongue and groove is very air permeable. Other than localized heat from the IC recessed light, is there any other reason to avoid these with regard to this roof design, or should they just not be used in this situation? Thanks.

Asked by Rick Schneider
Posted Nov 7, 2012 12:07 AM ET
Edited Nov 7, 2012 12:07 AM ET


6 Answers

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You are building an unvented cathedral ceiling that is insulated with a combination of spray foam and blown-in fiberglass or cellulose. Your plan is to use 1.5 inch of closed-cell spray foam, which has an R-value of about R-10.

Your plan will only work if you live in a warm climate (climate zone 1, 2, 3, or 4C). If you live in climate zone 4A, 4B, 5, or anywhere colder, your spray foam isn't thick enough. For more information on this issue, see How to Build an Insulated Cathedral Ceiling.

There are several reasons to avoid the use of recessed can lights in an insulated cathedral ceiling. The most important one (in your case): the fixture takes up room that should be filled with insulation, and introduces a hot spot right where your insulation is thinnest. As a result, you will suffer an energy penalty.

Answered by Martin Holladay
Posted Nov 7, 2012 9:27 AM ET
Edited Nov 7, 2012 9:28 AM ET.


Thanks for the reply. I'm in 4C climate zone, but at 1550 feet (Washington State, Olympic Penninsula) which is therefore colder. Besides the heat loss, I was very concerned about additional moisture in air escaping through the fixture. The article you referenced was very helpful.

Answered by Rick Schneider
Posted Nov 7, 2012 11:15 AM ET


We are doing something similar. We are in a mild climate (San Jose, CA area) and are building an unvented attic / cathedral ceiling in the kitchen/family room. I realize that recessed cans take up space where insulation should be and we suffer an energy penalty if we use them all over. Our goal is to not use them, but there is one area where I think we will need to have a few as we can not have a hanging light and there isn't a place for a wall sconce. Given that, are there ANY recessed lights that you could recommend? Thanks!

Answered by Laura T
Posted Jan 18, 2013 2:07 PM ET


I don't recommend that you do this.

However, you seem determined to proceed. Be sure to insulate as much of the compromised rafter bay as you can with rigid foam insulation or spray foam insulation.

Choose a fixture rated for insulation contact, and use so-called airtight trim. I recommend the use of an LED lamp.

Answered by Martin Holladay
Posted Jan 18, 2013 2:38 PM ET


There is just one spot where we can't seem to find a better solution, but I will keep trying. It's a breakfast nook area where anything hanging will block a window and I would rather not do it. I will keep searching for something that may work. Someone had mentioned using a remote transformer (?). Can't seem to figure out what they are referring to. Ideas?
Thank you so much!!!

Answered by Laura T
Posted Jan 18, 2013 3:56 PM ET


I have no idea whether your ceiling is flat or sloped. Nor do I know whether you like modern-looking light fixtures or traditional designs; nor whether you prefer rectangular light fixtures or circular ones.

Below is just one example of a surface-mounted fixture. There are hundreds of styles to choose from. Visit a lighting showroom and choose one you like.

Surface-mounted light fixtures.JPG
Answered by Martin Holladay
Posted Jan 18, 2013 4:08 PM ET

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