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insulating recessed lights in vaulted ceiling


remoh's Avatar
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MD

10-05-09, 04:05 PM   #1  
insulating recessed lights in vaulted ceiling

I'm getting ready to install 8 recessed lights in a newly framed addition.

The ceiling is vaulted so the lights will need to be mounted at an angle and I'll use fish-eye fixtures to direct the beams down.

Because the vault is so steep, it will be difficult to get R-30 insulation at the ends of the trusses (near the soffets). To deal with this, we're going to install foam panels that insure that air can flow from the soffet vents to the underside of the roof.

The recessed lights will fit but there won't be a lot of space above the (maybe 6-9 inches). The lights that I've purchased are 6 inch IC rated air tights from Utilitech.

My question is, do I need to place insulation (fiberglass roll type) on top of these lights or does it just need to be butted up against the lights on each side? How much will the leak if the top is exposed?

I've seen blown-in type insulation on top of recessed lights but that's not an option for me because of the pitch. Is it common to place fiberglass on top and if so does it need to be the same thickness? I'm afraid the R30 would touch the roof if placed on top of the lights.

Thanks for the help!

 
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Bud9051's Avatar
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10-06-09, 08:07 AM   #2  
Hi remoh, sloped ceilings are a challenge. Your choice of air sealed IC rated is good and should allow you to install the max amount of insulation possible.

A couple of points, since the ceiling is open, consider air baffles near the soffits to reduce wind washing on the end of the insulation, especially if you use fiberglass. Any air movement through the fiberglass just kills its insulation properties. The cellulose would block air flow, but you are concerned about the slope. Google "Roxul" a Canadian product that is showing up in the states. It appears to be what I would think of as a mineral wool. Probably not the right term, but Europe and Canada have been using that for a long time and one of my suppliers just added Roxul and I like it's density. May be worth looking at. I'm not connected to anyone, so not selling the product.

Also, to improve your overall r-value, you could add a layer of rigid before the drywall. It would add r-value and reduce the thermal bridging from the wood.

As far as energy loss if you don't get a lot of insulation directly over the lights, it will be minimal Say 10 lights at one sq. ft per light at half the r-value. When you average that into a 300 sq ft ceiling it doesn't make a lot of difference. What is important is the air sealed and sealing the cans to the sheetrock to eliminate leakage around them. I have seen water running out from condensation due to leaky cans, bad for r-value, bad for mold, bad for structure life.

You can also consider the CFLs or LED lights if they suit your lighting preferences.

Enjoy
Bud

 
remoh's Avatar
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10-07-09, 07:42 PM   #3  
Great. Thanks for the tips.

One more question. Is it typical to leave slack in the NM cable between lights? I was thinking that if I pull the cable tight between each light, it's going to compress the fiberglass insulation quite a bit. ...and compressed insulation doesn't work nearly as well.

Thanks again for the help!

 
Bud9051's Avatar
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10-08-09, 06:33 AM   #4  
Not an electrician, but I believe the cable should be secured to the side of the beams as you run from one to another. If you go over the top of the beams you need to run a 2x4 or 2x6 and secure to the edge so no one steps on it.

A quick post under the electrical group will give you a better answer.

Bud

 
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