# Vaulted Ceiling Insulation



## Joemaio87 (Nov 30, 2013)

Just recently purchased my first home. Built in 1959, it's a split level with vaulted ceilings throughout. We've taken it down to the studs and removed previous insulation (blown cellulose). The sheetrock ceiling was nailed to 2x6 joists, and from what I understand, the best I can go with fiberglass is r-19 but code is r-30 minimum. I also have read that in order to properly insulate, there needs to be a gap for breathing room above insulation. Spray foam is a little too far out of our price range. So the option I've seen most common is to place a 2x10 or 2x12 next to the 2x6's that are there and nail/bolt them together, then install r-30c or r38c for cathedral ceilings. My question is how is this as far as support once drywall is attached to these new joists, and do they need to run the entire length of the old 2x6 joist, or can i cut 2 foot pieces and sister them every few feet to save on lumber cost?

Can the 2x6 be extended further without sistering a new longer piece on the side of them? In other words, somehow attach another 2x4 or 2x6 straight down from the existing structure? Getting the ceilings properly insulated is a big concern for me for efficiency, but I'd like to get some opinions on how to go about this.

Thanks!


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## Gary in WA (Mar 11, 2009)

Sistering new may work, as might adding pieces or even furring down with new rafters below old with plywood gussets; depends on span rating of old rafters; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_8_par027.htm?bu2=undefined

The airway should be separated from the fibrous cavity insulation (for no R-value loss) with baffles or foamboard; http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting

Gary


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## joecaption (Nov 30, 2011)

May want to consider this brand of insulation. 
http://www.roxul.com/products/residential/roxul+comfortbatt


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## Joemaio87 (Nov 30, 2013)

Should have mentioned that spacing throughout house is 16 on center for ceiling and walls. Floor joists are 24 OC. Sistering seems to be a good option, but adds about 1500-2000 dollars to the insulation cost in lumber. How exactly does a plywood gusset work? Attach to both sides of existing 2x6 and then attach another 2x6 underneath? Seems like that may be a good option assuming it can structurally support lighting and drywall. Appreciate the help so far, thank you!


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## Gary in WA (Mar 11, 2009)

Work with your local AHJ, they will be inspecting it. Let us know what they accepted, thanks!

Gary


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## Nailbags (Feb 1, 2012)

Gary in WA said:


> Work with your local AHJ, they will be inspecting it. Let us know what they accepted, thanks!
> 
> Gary


Gutting a home in most places does not require a permit or inspection of any kind.


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## Gary in WA (Mar 11, 2009)

Same with around here. The OP may be adding wood to the existing rafters, we don't know the span/species of those rafters or the new loads that he will be adding in his structural changes. The rafters may be below minimum code requirements now, or close to them, adding additional weight could be problematic. I don't want that liability.

Gary


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## Joemaio87 (Nov 30, 2013)

I'd much rather NOT go through all the additional labor and lumber charges just to get the ceilings insulated at r-30. I just haven't heard of any ideas that can achieve this aside from extending the joists, and even that hasn't been fully explained on how it can be achieved.


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## Gary in WA (Mar 11, 2009)

Use rigid foam board in the rafter cavities with no air space, as the map shows in the second link I gave previously;http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting


You require (using your R-30 statement) R-5 against the sheathing to prevent condensation. But without furring the rafters; 5-1/2" of foam board will give; 2" of [email protected] per in. and 3-1/2" of XPS @ R-5 per in. = 13 + 17.5= R-30.5 Similar to Fig.2- except you would have all fb;http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting

Gary


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## Joemaio87 (Nov 30, 2013)

Gary, I appreciate your responses so far. If I were to use all foam board with no air space, than wouldn't the roof deck not be properly vented?


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## Joemaio87 (Nov 30, 2013)

Also, will ridgid foam affect the installation of can lights since there is less volume to work with?


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## Gary in WA (Mar 11, 2009)

Joemaio87 said:


> Gary, I appreciate your responses so far. If I were to use all foam board with no air space, than wouldn't the roof deck not be properly vented?


Yes, it would not be vented; http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation?full_view=1

http://www.buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates

"Also, will ridgid foam affect the installation of can lights since there is less volume to work with?"----------------- yes, you should not use can lights in a cathedral ceiling.

Gary


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## Nubie Seabee (Dec 4, 2013)

Hi Joe,

You and I are in the same situation. I reside in Southern California so we should have the same R-value. My inspiration was looking at my neighbors vaulted ceiling that also has recessed lighting. The layout of her kitchen was the same as mine so I wanted to mimic hers. I looked at the contractors work when I crawled In her attic, and it seemed like he just built rafters by 2x4 held by 4x6 at the peak. He built it lower than the pre existing rafters but had the same angle. With that he was able to attached the insulation and the recessed lighting with ease. I have attached pictures of my unfinished kitchen, and my neighbors finished kitchen, as well as the framing from the attics point of view. My only concern was building the rafters by 2x4 I would at least built it with 2x6. I hope this helps. If you figured out another way that is cost effective let me know.


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## Joemaio87 (Nov 30, 2013)

Nubie Seabee said:


> Hi Joe,
> 
> You and I are in the same situation. I reside in Southern California so we should have the same R-value. My inspiration was looking at my neighbors vaulted ceiling that also has recessed lighting. The layout of her kitchen was the same as mine so I wanted to mimic hers. I looked at the contractors work when I crawled In her attic, and it seemed like he just built rafters by 2x4 held by 4x6 at the peak. He built it lower than the pre existing rafters but had the same angle. With that he was able to attached the insulation and the recessed lighting with ease. I have attached pictures of my unfinished kitchen, and my neighbors finished kitchen, as well as the framing from the attics point of view. My only concern was building the rafters by 2x4 I would at least built it with 2x6. I hope this helps. If you figured out another way that is cost effective let me know.


This seems to be the route I will most likely go. I priced out rigid foam for the living room alone and it was over 3k to achieve r-value of around 33. I originally wanted to just sister 2x12's but at around $30 for a 16 foot piece, the living room alone is around $500 in lumber. So a dropped ceiling seems most cost effective and keeps the roof deck vented with r-30 or r-38 depending how much room I want to lose.

There is a header at the peak like in your pictures, is that where you are saying the 4x6 was added to hold the new 2x4 joists? How were they supported at the other end?


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